essay questions about evolution

The Theory of Evolution by Natural Selection

Charles Darwin, a renowned scientist and naturalist, introduced the groundbreaking theory of evolution in the 19th century. Darwin's theory challenged prevailing beliefs and forever changed our understanding of the natural world. Through careful observation and extensive research, Darwin proposed that species evolve over time through a process called natural selection .

He suggested that individuals with advantageous traits are more likely to survive and reproduce, passing on these favorable traits to future generations. This gradual and continuous process leads to the formation of new species and the diversity of life on Earth. Darwin's theory of evolution had a profound impact on scientific thought and continues to be the foundation of modern biology.

Selected Essays for Assessments

This assignment can be modified or the questions can be used as part of a unit assessment. Assigning all of the essays can be overwhelming, but useful for prompting discussions and developing a more in depth understganding of the topics.

Essays can be developed as a group, where students discuss the topic and develop their essays or lead a class discussion. Alternatively, students can post on learning management systems, like Google Classroom.

1. Does evolution through natural selection produce "better" organisms in an absolute sense? Are we climbing the Scala Naturae ? Defend your answer

2. The idea of special creation and the study of fossils have each had an impact on evolutionary thought. Discuss why one is considered a scientific endeavor and the other not scientific.

3. In what sense are humans currently acting as "agents of selection" on other species?

Name some organisms that are favored by the environmental changes humans cause.

4. Describe the three types of natural selection.

Which type(s) are mores likely to occur in stable environments and which type(s) in rapidly changing environments? Defend your answer.

5. What is sexual selection? How is sexual selection similar to and different from other forms of natural selection?

6. By the 1940's the Whooping Crane population had been reduced to under 50 individuals. Thanks to conservation measures, their numbers are now increasing. But what special evolutionary problems do the Whooping Cranes have after passing through a population bottleneck?

7. Do phyletic speciation and divergent speciation coincide with the gradualism and punctuated equilibrium models of evolution? Defend your answer

8. Why do you suppose there are so many endemic species on islands? (Endemic means "found nowhere else") Why have an overwhelming majority of recent extinctions occurred on islands?

9. In southern Wisconsin there are several populations of gray squirrels with black fur. Design a study to determine if they are actually a separate species. Explain why it is difficult to gather data about speciation events.

10. Describe the evolutionary trends of primates - from early primates to humans. Include in your discussion such features as binocular vision, grasping hands, bipedal locomotion, social living, tool making, and brain expansion

11. Explore how ecological interactions, such as predation and competition, contribute to the process of evolution. Use specific examples to support your explanation.

12. In 1981, The Big Bird lineage became reproductively isolated from G. fortis on Daphne Major.

a) Describe one prezygotic mechanism that likely contributed to the reproductive isolation of the Big Bird lineage from G. fortis. b) Based on the data in Figure 1, explain why the Big Bird population has been able to survive and reproduce on Daphne Major.

Evolution Resources for AP Biology

Slides:  18a Origins  |  18b Speciation  |  18c Evidence Slides: Evolution of Populations|  Guided Notes Anole Lizard Temperature (CER) Evolution and Chernobyl Tree Frogs Lizards in a Hurricane  |  Slides Virginia Opossum Latitude Variations  | Slides Tale of Speciation on Daphne Major

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120 Evolution Essay Topic Ideas & Examples

Inside This Article

Evolution is a fascinating topic that has captivated scientists and scholars for centuries. From the origins of life to the development of complex organisms, the study of evolution has provided valuable insights into the history of our planet and the diversity of life on Earth. If you're interested in exploring this complex and intriguing subject, we've compiled a list of 120 evolution essay topic ideas and examples to help spark your creativity and inspire your research.

• The Theory of Evolution: An Overview
• Darwin's Theory of Natural Selection
• The Evidence for Evolution
• Evolutionary Biology: The Study of Evolution
• The Evolution of Humans
• The Evolution of Birds
• The Evolution of Whales
• The Evolution of Insects
• The Evolution of Plants
• The Evolution of Fish
• The Evolution of Reptiles
• The Evolution of Mammals
• The Evolution of Primates
• The Evolution of Dinosaurs
• The Evolution of Fossils
• The Evolution of Genetics
• The Evolution of DNA
• The Evolution of Development
• The Evolution of Behavior
• The Evolution of Ecology
• The Evolution of Speciation
• The Evolution of Adaptation
• The Evolution of Extinction
• The Evolution of Migration
• The Evolution of Reproduction
• The Evolution of Diversity
• The Evolution of Complexity
• The Evolution of Cooperation
• The Evolution of Competition
• The Evolution of Symbiosis
• The Evolution of Parasitism
• The Evolution of Mutualism
• The Evolution of Predation
• The Evolution of Herbivory
• The Evolution of Carnivory
• The Evolution of Omnivory
• The Evolution of Trophic Levels
• The Evolution of Ecosystems
• The Evolution of Biomes
• The Evolution of Climate
• The Evolution of Ice Ages
• The Evolution of Mass Extinctions
• The Evolution of Biodiversity
• The Evolution of Endemism
• The Evolution of Invasive Species
• The Evolution of Conservation
• The Evolution of Restoration
• The Evolution of Evolutionary Theory
• The Evolution of Creationism
• The Evolution of Intelligent Design
• The Evolution of Lamarckism
• The Evolution of Epigenetics
• The Evolution of Horizontal Gene Transfer
• The Evolution of Gene Duplication
• The Evolution of Gene Regulation
• The Evolution of Gene Expression
• The Evolution of Gene Networks
• The Evolution of Genetic Drift
• The Evolution of Gene Flow
• The Evolution of Genetic Variation
• The Evolution of Genetic Diversity
• The Evolution of Genetic Structure
• The Evolution of Genetic Isolation
• The Evolution of Genetic Speciation
• The Evolution of Genetic Adaptation
• The Evolution of Genetic Inheritance
• The Evolution of Genetic Mutations
• The Evolution of Genetic Recombination
• The Evolution of Genetic Mapping
• The Evolution of Genetic Engineering
• The Evolution of Genetic Testing
• The Evolution of Genetic Counseling
• The Evolution of Genetic Modification
• The Evolution of Genetic Sequencing
• The Evolution of Genetic Algorithms
• The Evolution of Genetic Programming
• The Evolution of Genetic Algorithms in Artificial Intelligence
• The Evolution of Genetic Algorithms in Machine Learning
• The Evolution of Genetic Algorithms in Robotics
• The Evolution of Genetic Algorithms in Bioinformatics
• The Evolution of Genetic Algorithms in Medicine
• The Evolution of Genetic Algorithms in Agriculture
• The Evolution of Genetic Algorithms in Industry
• The Evolution of Genetic Algorithms in Finance
• The Evolution of Genetic Algorithms in Marketing
• The Evolution of Genetic Algorithms in Education
• The Evolution of Genetic Algorithms in Sports
• The Evolution of Genetic Algorithms in Gaming
• The Evolution of Genetic Algorithms in Entertainment
• The Evolution of Genetic Algorithms in Art
• The Evolution of Genetic Algorithms in Music
• The Evolution of Genetic Algorithms in Literature
• The Evolution of Genetic Algorithms in Film
• The Evolution of Genetic Algorithms in Television
• The Evolution of Genetic Algorithms in Theater
• The Evolution of Genetic Algorithms in Dance
• The Evolution of Genetic Algorithms in Fashion
• The Evolution of Genetic Algorithms in Architecture
• The Evolution of Genetic Algorithms in Design
• The Evolution of Genetic Algorithms in Technology
• The Evolution of Genetic Algorithms in Science
• The Evolution of Genetic Algorithms in Engineering
• The Evolution of Genetic Algorithms in Mathematics
• The Evolution of Genetic Algorithms in Physics
• The Evolution of Genetic

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100 Evolution Essay Topics + Essay Writing Guide

Even though most of us know enough about evolution, finding a good and a unique topic can quickly become a challenge! The trick here is to determine a unique framework for your future paper, so you know what structure to follow to keep up with all the essay writing rules. Looking through the countless Biology and Life Sciences essays of the actual students and reading through essay revisions of college and university professors in our time, I have made a list of 100 excellent evolution essay topics and wrote down all the “Do’s” and “Don’t’s” of evolution essay writing.

Trust me, choosing a good topic becomes much easier when you understand how the evolution works and realize that it deals with much more than explaining how we all got here. It is not only about us, human beings, as evolution also deals with all flora and fauna and the changes that take place in our society. As you read through the topics below, think of evolution as of diversity in nature that provides a framework for the determination of the ways how the species develop their distinguishable differences!

Contents (Clickable)

      What is an Evolution Essay?

Evolution essay is a paper that focuses on any aspect related to the evolution theory and diversity in nature. Since it is a scientific theory that is fundamental for the modern biological theory, an evolution essay also includes the facts, theories, hypotheses, and the history of the evolution theory among other topics. Evolution essay is first and foremost, a scientific work, therefore, it is extremely important to include verified facts, backed up with the help of academic journals and the books with a correct format and the references.

      Evolution and Theory of Evolution

A bit more theory that will help you to understand the topics in a better way! Trust me; I’ll keep it short!

Evolution refers to changes in heritable characteristics in species over successive generations. This process ultimately results in the occurrence of biodiversity (this is the reason why the presence of Biodiversity in your research paper is so important!). In basic terms, evolution is a process that occurs in all species on Earth, which are currently estimated at mind-blowing 2 million . In other words, it means all the species, starting with miniscule bacteria and up to the evolution of human beings.

Theory of evolution refers to a scientific theory that explains the origin of different species by evolution. Charles Darwin is considered to be the father of the theory of evolution and the one behind the foundation of the theory explained in the famous On the Origin of Species book published in 1859.

      Actual Research Essay Examples on Topic!

Before we move on to the list of 100 evolution essay topics, I want to share four actual essay examples related to evolution, biology, and the life sciences, so you can get a better idea about how particular ideas can be implemented in practice for the best results. Looking through our vast essay database written and shared by students, I came up with these diverse examples:

• Global Warming: Fact or Fiction? – Evolution explored through the phenomenon of global warming. Is it a fact or a fiction? This essay’s author came up with an excellent research topic and argumentation!
• Environmental Science Q&A – Here we have an example of environmental issues related to evolution and the changes that we can observe. See how the questions are addressed and how the structure is kept.
• Genetically Modified Food – As surprising as it may be, it is also an issue related to evolution because the microorganisms and the species go through mutation, which is, essentially, an evolution process and a relevant social issue.
• Geographical Characteristics of the Streams in Urban Areas and Forested Areas – see how the changes of evolution impact the geographical aspect in both urban and the forested areas.

As you can see from the examples, evolution is an expansive concept and a field of research, so you do not have to limit yourself with a strict list of biology or microorganisms-related topics. Be creative and try to make your evolution essay feel interesting and inspiring!

     100 Evolution Essay Topics

Let us start with the human evolution, so we can see how broad and many-sided the evolution essay writing can be!

      Human Evolution Essay Topics

• Why do human beings laugh?
• Why did human species develop to be dominant on the planet?
• What distinguishes human brain from the other species?
• Evolution of human eye.
• Why do human beings perceive beauty?
• How does evolution theory explain the existence of language and speech?
• Recent mutations the humans underwent.
• The current mutations humans are going through.
• Geodakyan evolutionary theory of sex.
• Evolution of sexual reproduction.
• Red Queen hypothesis.
• Evolution of human intelligence.
• Evolution of monogamy.
• Evolutionary medicine.
• Social effects of evolutionary theory.
• Evolution of immunity.
• Evolution of the human nervous system.
• Evolution of sex differences in cognition.
• Sexual selection.
• Sexual conflict.
• Host-parasite coevolution in human malaria.
• Variation in evolution.
• Evolutionary stance on art.
• Why did humans start walking on two feet?
• What is the evolutionary benefit of forming the society?
• As you can see from these examples, evolution is not only about biology and the life sciences!

Okay, so you want something more traditional? Here we go below:

      Evolution of Flora and Fauna Essay Topics

• Evolution of dogs/cats/whales/ or any other species of your choice.
• Parallel evolution in the animal kingdom.
• Earliest life forms.
• Cladistics in the animal kingdom.
• Evolutionary ecology of parasites.
• Host-parasite coevolution in animals.
• Evolution of birds.
• An impact of climate on evolution.
• Evolution of fungi.
• The hair evolution.
• Notable cases of adaptation.
• Evolution of mimicry.
• Natural selection in the animal kingdom.
• Co-operation development.
• Early animal evolution.
• Polyps and medusas evolution.
• “Savannah” hypothesis of early bilateral evolution.
• Why the invertebrates became more complex?
• Evolution of the animal genome.
• Early evolution of neurons.
• Plant population genetics and evolution.
• Reconstruction of sexual modes throughout evolution.
• The role of chromosomal change in plant evolution.
• Evolution during the domestication of animals.

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Let’s continue with more biology-related topics!

      Evolutionary Biology Essay Topics

• Gene-centered view.
• Theory of stellar evolution.
• The social impact of evolutionary biology.
• Evolution of multicellular organisms.
• Genetic architecture of adaptation.
• Evolutionary robotics.
• Evolution of cooperation.
• Paleobiology.
• Bayesian inference of phylogeny and its impact on evolutionary biology.
• Evolutionary biology of aging.
• Neuroscience in evolutionary biology.
• Optimality theory.
• Morphometrics.
• Biological conservation.
• Evolutionary biology and ecology.
• Evolutionary biology and immunology.
• Conceptual issues in evolutionary biology.
• Evolutionary biology and population genetics.
• Evolutionary biology and phylogenetics.
• Mathematical models in evolutionary biology.
• The evolutionary perspective on sperm biology.
• Plant speciation.
• Marine speciation.
• Morphological evolution.

      Theory of Evolution Essay Topics

• How did Darwin come up with his theory?
• Theories that can potentially debunk an evolution theory.
• Common misconceptions about evolution that everyone still believes.
• Influence of Darwin’s theory on the science.
• History of evolutionary thought.
• Theories about evolution that existed before Darwin’s “ The Origin of Species”
• Essentialism.
• Tree of Life Concept.
• Are we all related?
• Adaptation theory.
• Lamarck’s theory of evolution.
• Evolution as fact and the theory.
• Somatic selection.
• Synthetic theory of evolution.
• Why is evolution still considered a theory?
• Evolution theory of a social change.
• Evolutionary psychology.
• Mutation theory by De Vries.
• Neo-Darwinism.
• The types of evolutionary theories.
• The contribution of Alfred Wallace in the evolution theory.
• Who should be credited for evolution theory – Wallace or Darwin?
• Objections to evolution theory.
• Proof of evolution.
• How does evolution explain morality?

      How to Write an Evolution Essay

1 Evolution Essay Structure

The structure of an evolution essay is what you should know even before you decide on a topic and there is a good reason for that! There are three major elements that your essay structure should include to make sure that your professor will not decrease your future grade:

• Introduction . It provides the readers with a brief outlook on your topic, your essay structure, the elements included, and the main idea that you want to communicate. It is where your strong thesis statement or an argument go to! Make sure your introduction contains the following:
• A strong hook sentence – an attention-grabbing element that is usually in the first 1-2 sentences of the essay. Since we have to write an essay about the evolution theory, we will choose a scientific fact or refer to an impressive discovery that refers to evolution. A reason why hook should be there is to capture your reader’s interest and attention!
• Overview of your major argument and topic – let the readers know what they are about to find out and learn as they read your evolution essay!
• A brief overview of the essay structure – explain how and in what order you are planning to develop each part of your paper.
• Thesis statement – the main idea or the quintessence of your essay. Make sure to write several thesis statements and choose the one that not only sounds best but the one that you can back up and explain with the help of scientific data and credible references.
• Body paragraph includes the consistent and logical sequence of paragraphs that reveal all the facts and arguments that you use to support your thesis statement.

Make sure to:

• Use verified sources – evolution theory is a scientific theory that has plenty of evidence, so make sure that you include as many credible references as necessary!
• Be logical and consistent – let your readers follow your logic easily. Remember that your audience may differ, so make sure to write a sentence or two that explains your vision and the concepts you are discussing. If it requires more work or a reference to a case study, make sure to include it in your paper.
• Start every paragraph with a topic sentence – it will be much easier for you to write each section if you start writing them with a thesis that reflects the content of the paragraph.
• Explain the facts included in the essay – demonstrate your understanding of the facts you use in the essay and their relevance to the main topic and thesis statement
• Avoid plagiarism – copying someone else’s work without reference is not cool while using numerous sources to support your thought with an academic claim is entirely another thing that makes your essay look credible and professional!
• Conclusion part is where you summarize the whole essay without the introduction of any new ideas . Remind your readers of the most important facts and the findings they should remember when they are done reading your essay. Restate your thesis statement in other words to make the essay sound logical and integrated.

2 Argumentative Essay on Evolution Writing Tricks

When you have to write an argumentative essay on evolution, there are some writing tricks that you should mind to avoid trouble with your paper and impress your college or university professor.

• Include your own opinion on an issue that you discuss – an argumentative essay requires having your own stance on a problem or what most college professors call “a voice of the writer.” Ask yourself about how can YOU contribute to the issue since it is your paper and it has to stand out!
• Defend your view on the issue using as many verified facts as you can!
• Include the viewpoints that oppose yours – and prove them wrong . Do so with the facts and use strong reasoning.
• Do not simply restate thesis statement in conclusion , but readdress it using the evidence you accumulated through the body paragraphs.
• Use classic 5-paragraph essay format (if you are not required to do otherwise) – Introduction, 3 Body Paragraphs, and Conclusion. Such an approach will help you to see where all that information belongs!

      Evolution Essay “Do’s and Dont’s”

• Research your facts, the background of the issue, and the case studies (if relevant) as you choose your future topic and read the list of topic examples below.
• Include scientific facts in your essay and use professional language.
• Start your introduction with an interesting hook by stating why is the topic of choice relevant to you and society.
• Use strong thesis statement as your guideline to make sure that you don’t deviate from the topic.
• Double-check your facts and always back up your paper with academic journals and credible references.
• Do not underestimate the use of drafts as you write the paper.
• Do not use the same wording for the thesis statement as for your hook sentence. These are two different matters where one of them is an introduction, and the other one is the reason for your research.
• Do not simply copy scientific information without your personal comment and consideration. If it has to be there, explain how and why.
• Do not underestimate the importance of an outline, format, and the body structure.
• Do not ignore the importance of proofreading because it will help you to eliminate typos, grammar mistakes, and accidental repeating of the same sentence.

      Help! I’m Still Stuck!!!

Sometimes even the list of helpful topic ideas and the essay writing guides are still not enough because the deadline is coming up and you have not yet started. In other cases, it is way too difficult to find the right sources, and you need just a bit of help to get your paper done. It is exactly the moment when you need professional help and someone who can help you get out of this “I’m Stuck!” mode.

The help is already here for you as our skilled team of biology and life sciences experts, as well as professionals in the other fields of science, are ready to help you work through the most complex assignments and be there to make you come up with a great topic idea! All you have to do is tell us of your homework task, fill in the simple form, and we shall connect you with a skilled geek who knows how to help and do so timely! It is absolutely safe and confidential, let alone that it is fine to ask for help when you need it! Our team knows how much challenging all of these tasks are, so it is guaranteed that you will be guided through each problem and issue that you have to deliver a great final paper. No matter what your problem may be, we are ready to help you identify and deal with it!

I am sincerely hoping that my 100 evolution essay topics and the writing guide article have helped you to get an idea of how to write your paper. If not, remember what I have mentioned in a paragraph above! 🙂 In case you have something to add or want to share something important, feel free to post in the comments below! I wish you the best of luck and let us make an evolution with a truly awesome paper!

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Introductory essay

Written by the educator who created What Makes Us Human?, a brief look at the key facts, tough questions and big ideas in his field. Begin this TED Study with a fascinating read that gives context and clarity to the material.

As a biological anthropologist, I never liked drawing sharp distinctions between human and non-human. Such boundaries make little evolutionary sense, as they ignore or grossly underestimate what we humans have in common with our ancestors and other primates. What's more, it's impossible to make sharp distinctions between human and non-human in the paleoanthropological record. Even with a time machine, we couldn't go back to identify one generation of humans and say that the previous generation contained none: one's biological parents, by definition, must be in the same species as their offspring. This notion of continuity is inherent to most evolutionary perspectives and it's reflected in the similarities (homologies) shared among very different species. As a result, I've always been more interested in what makes us similar to, not different from, non-humans.

Evolutionary research has clearly revealed that we share great biological continuity with others in the animal kingdom. Yet humans are truly unique in ways that have not only shaped our own evolution, but have altered the entire planet. Despite great continuity and similarity with our fellow primates, our biocultural evolution has produced significant, profound discontinuities in how we interact with each other and in our environment, where no precedent exists in other animals. Although we share similar underlying evolved traits with other species, we also display uses of those traits that are so novel and extraordinary that they often make us forget about our commonalities. Preparing a twig to fish for termites may seem comparable to preparing a stone to produce a sharp flake—but landing on the moon and being able to return to tell the story is truly out of this non-human world.

Humans are the sole hominin species in existence today. Thus, it's easier than it would have been in the ancient past to distinguish ourselves from our closest living relatives in the animal kingdom. Primatologists such as Jane Goodall and Frans de Waal, however, continue to clarify why the lines dividing human from non-human aren't as distinct as we might think. Goodall's classic observations of chimpanzee behaviors like tool use, warfare and even cannibalism demolished once-cherished views of what separates us from other primates. de Waal has done exceptional work illustrating some continuity in reciprocity and fairness, and in empathy and compassion, with other species. With evolution, it seems, we are always standing on the shoulders of others, our common ancestors.

Primatology—the study of living primates—is only one of several approaches that biological anthropologists use to understand what makes us human. Two others, paleoanthropology (which studies human origins through the fossil record) and molecular anthropology (which studies human origins through genetic analysis), also yield some surprising insights about our hominin relatives. For example, Zeresenay Alemsegad's painstaking field work and analysis of Selam, a 3.3 million-year old fossil of a 3-year-old australopithecine infant from Ethiopia, exemplifies how paleoanthropologists can blur boundaries between living humans and apes.

Selam, if alive today, would not be confused with a three-year-old human—but neither would we mistake her for a living ape. Selam's chimpanzee-like hyoid bone suggests a more ape-like form of vocal communication, rather than human language capability. Overall, she would look chimp-like in many respects—until she walked past you on two feet. In addition, based on Selam's brain development, Alemseged theorizes that Selam and her contemporaries experienced a human-like extended childhood with a complex social organization.

Fast-forward to the time when Neanderthals lived, about 130,000 – 30,000 years ago, and most paleoanthropologists would agree that language capacity among the Neanderthals was far more human-like than ape-like; in the Neanderthal fossil record, hyoids and other possible evidence of language can be found. Moreover, paleogeneticist Svante Pääbo's groundbreaking research in molecular anthropology strongly suggests that Neanderthals interbred with modern humans. Paabo's work informs our genetic understanding of relationships to ancient hominins in ways that one could hardly imagine not long ago—by extracting and comparing DNA from fossils comprised largely of rock in the shape of bones and teeth—and emphasizes the great biological continuity we see, not only within our own species, but with other hominins sometimes classified as different species.

Though genetics has made truly astounding and vital contributions toward biological anthropology by this work, it's important to acknowledge the equally pivotal role paleoanthropology continues to play in its tandem effort to flesh out humanity's roots. Paleoanthropologists like Alemsegad draw on every available source of information to both physically reconstruct hominin bodies and, perhaps more importantly, develop our understanding of how they may have lived, communicated, sustained themselves, and interacted with their environment and with each other. The work of Pääbo and others in his field offers powerful affirmations of paleoanthropological studies that have long investigated the contributions of Neanderthals and other hominins to the lineage of modern humans. Importantly, without paleoanthropology, the continued discovery and recovery of fossil specimens to later undergo genetic analysis would be greatly diminished.

Molecular anthropology and paleoanthropology, though often at odds with each other in the past regarding modern human evolution, now seem to be working together to chip away at theories that portray Neanderthals as inferior offshoots of humanity. Molecular anthropologists and paleoanthropologists also concur that that human evolution did not occur in ladder-like form, with one species leading to the next. Instead, the fossil evidence clearly reveals an evolutionary bush, with numerous hominin species existing at the same time and interacting through migration, some leading to modern humans and others going extinct.

Molecular anthropologist Spencer Wells uses DNA analysis to understand how our biological diversity correlates with ancient migration patterns from Africa into other continents. The study of our genetic evolution reveals that as humans migrated from Africa to all continents of the globe, they developed biological and cultural adaptations that allowed for survival in a variety of new environments. One example is skin color. Biological anthropologist Nina Jablonski uses satellite data to investigate the evolution of skin color, an aspect of human biological variation carrying tremendous social consequences. Jablonski underscores the importance of trying to understand skin color as a single trait affected by natural selection with its own evolutionary history and pressures, not as a tool to grouping humans into artificial races.

For Pääbo, Wells, Jablonski and others, technology affords the chance to investigate our origins in exciting new ways, adding pieces into the human puzzle at a record pace. At the same time, our technologies may well be changing who we are as a species and propelling us into an era of "neo-evolution."

Increasingly over time, human adaptations have been less related to predators, resources, or natural disasters, and more related to environmental and social pressures produced by other humans. Indeed, biological anthropologists have no choice but to consider the cultural components related to human evolutionary changes over time. Hominins have been constructing their own niches for a very long time, and when we make significant changes (such as agricultural subsistence), we must adapt to those changes. Classic examples of this include increases in sickle-cell anemia in new malarial environments, and greater lactose tolerance in regions with a long history of dairy farming.

Today we can, in some ways, evolve ourselves. We can enact biological change through genetic engineering, which operates at an astonishing pace in comparison to natural selection. Medical ethicist Harvey Fineberg calls this "neo-evolution". Fineberg goes beyond asking who we are as a species, to ask who we want to become and what genes we want our offspring to inherit. Depending on one's point of view, the future he envisions is both tantalizing and frightening: to some, it shows the promise of science to eradicate genetic abnormalities, while for others it raises the specter of eugenics. It's also worth remembering that while we may have the potential to influence certain genetic predispositions, changes in genotypes do not guarantee the desired results. Environmental and social pressures like pollution, nutrition or discrimination can trigger "epigenetic" changes which can turn genes on or off, or make them less or more active. This is important to factor in as we consider possible medical benefits from efforts in self-directed evolution. We must also ask: In an era of human-engineered, rapid-rate neo-evolution, who decides what the new human blueprints should be?

Technology figures in our evolutionary future in other ways as well. According to anthropologist Amber Case, many of our modern technologies are changing us into cyborgs: our smart phones, tablets and other tools are "exogenous components" that afford us astonishing and unsettling capabilities. They allow us to travel instantly through time and space and to create second, "digital selves" that represent our "analog selves" and interact with others in virtual environments. This has psychological implications for our analog selves that worry Case: a loss of mental reflection, the "ambient intimacy" of knowing that we can connect to anyone we want to at any time, and the "panic architecture" of managing endless information across multiple devices in virtual and real-world environments.

Despite her concerns, Case believes that our technological future is essentially positive. She suggests that at a fundamental level, much of this technology is focused on the basic concerns all humans share: who am I, where and how do I fit in, what do others think of me, who can I trust, who should I fear? Indeed, I would argue that we've evolved to be obsessed with what other humans are thinking—to be mind-readers in a sense—in a way that most would agree is uniquely human. For even though a baboon can assess those baboons it fears and those it can dominate, it cannot say something to a second baboon about a third baboon in order to trick that baboon into telling a fourth baboon to gang up on a fifth baboon. I think Facebook is a brilliant example of tapping into our evolved human psychology. We can have friends we've never met and let them know who we think we are—while we hope they like us and we try to assess what they're actually thinking and if they can be trusted. It's as if technology has provided an online supply of an addictive drug for a social mind evolved to crave that specific stimulant!

Yet our heightened concern for fairness in reciprocal relationships, in combination with our elevated sense of empathy and compassion, have led to something far greater than online chats: humanism itself. As Jane Goodall notes, chimps and baboons cannot rally together to save themselves from extinction; instead, they must rely on what she references as the "indomitable human spirit" to lessen harm done to the planet and all the living things that share it. As Goodall and other TED speakers in this course ask: will we use our highly evolved capabilities to secure a better future for ourselves and other species?

I hope those reading this essay, watching the TED Talks, and further exploring evolutionary perspectives on what makes us human, will view the continuities and discontinuities of our species as cause for celebration and less discrimination. Our social dependency and our prosocial need to identify ourselves, our friends, and our foes make us human. As a species, we clearly have major relationship problems, ranging from personal to global scales. Yet whenever we expand our levels of compassion and understanding, whenever we increase our feelings of empathy across cultural and even species boundaries, we benefit individually and as a species.

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Zeresenay Alemseged

The search for humanity's roots, relevant talks.

We are all cyborgs now

Frans de Waal

Moral behavior in animals.

Harvey Fineberg

Are we ready for neo-evolution.

Jane Goodall

What separates us from chimpanzees.

Nina Jablonski

Skin color is an illusion.

Spencer Wells

A family tree for humanity.

Svante Pääbo

Dna clues to our inner neanderthal.

18.1 Understanding Evolution

Learning objectives.

By the end of this section, you will be able to do the following:

• Describe how scientists developed the present-day theory of evolution
• Define adaptation
• Explain convergent and divergent evolution
• Describe homologous and vestigial structures
• Discuss misconceptions about the theory of evolution

Evolution by natural selection describes a mechanism for how species change over time. Scientists, philosophers, researchers, and others had made suggestions and debated this topic well before Darwin began to explore this idea. Classical Greek philosopher Plato emphasized in his writings that species were static and unchanging, yet there were also ancient Greeks who expressed evolutionary ideas. In the eighteenth century, naturalist Georges-Louis Leclerc Comte de Buffon reintroduced ideas about the evolution of animals and observed that various geographic regions have different plant and animal populations, even when the environments are similar. Some at this time also accepted that there were extinct species.

Also during the eighteenth century, James Hutton, a Scottish geologist and naturalist, proposed that geological change occurred gradually by accumulating small changes from processes operating like they are today over long periods of time. This contrasted with the predominant view that the planet's geology was a consequence of catastrophic events occurring during a relatively brief past. Nineteenth century geologist Charles Lyell popularized Hutton's view. A friend to Darwin. Lyell’s ideas were influential on Darwin’s thinking: Lyell’s notion of the greater age of Earth gave more time for gradual change in species, and the process of change provided an analogy for this change. In the early nineteenth century, Jean-Baptiste Lamarck published a book that detailed a mechanism for evolutionary change. We now refer to this mechanism as an inheritance of acquired characteristics by which the environment causes modifications in an individual, or offspring could use or disuse of a structure during its lifetime, and thus bring about change in a species. While many discredited this mechanism for evolutionary change, Lamarck’s ideas were an important influence on evolutionary thought.

Charles Darwin and Natural Selection

In the mid-nineteenth century, two naturalists, Charles Darwin and Alfred Russel Wallace, independently conceived and described the actual mechanism for evolution. Importantly, each naturalist spent time exploring the natural world on expeditions to the tropics. From 1831 to 1836, Darwin traveled around the world on H.M.S. Beagle , including stops in South America, Australia, and the southern tip of Africa. Wallace traveled to Brazil to collect insects in the Amazon rainforest from 1848 to 1852 and to the Malay Archipelago from 1854 to 1862. Darwin’s journey, like Wallace’s later journeys to the Malay Archipelago, included stops at several island chains, the last being the Galápagos Islands west of Ecuador. On these islands, Darwin observed species of organisms on different islands that were clearly similar, yet had distinct differences. For example, the ground finches inhabiting the Galápagos Islands comprised several species with a unique beak shape ( Figure 18.2 ). The species on the islands had a graded series of beak sizes and shapes with very small differences between the most similar. He observed that these finches closely resembled another finch species on the South American mainland. Darwin imagined that the island species might be species modified from one of the original mainland species. Upon further study, he realized that each finch's varied beaks helped the birds acquire a specific type of food. For example, seed-eating finches had stronger, thicker beaks for breaking seeds, and insect-eating finches had spear-like beaks for stabbing their prey.

Wallace and Darwin both observed similar patterns in other organisms and they independently developed the same explanation for how and why such changes could take place. Darwin called this mechanism natural selection. Natural selection , or “survival of the fittest,” is the more prolific reproduction of individuals with favorable traits that survive environmental change because of those traits. This leads to evolutionary change.

For example, Darwin observed a population of giant tortoises in the Galápagos Archipelago to have longer necks than those that lived on other islands with dry lowlands. These tortoises were “selected” because they could reach more leaves and access more food than those with short necks. In times of drought when fewer leaves would be available, those that could reach more leaves had a better chance to eat and survive than those that couldn’t reach the food source. Consequently, long-necked tortoises would be more likely to be reproductively successful and pass the long-necked trait to their offspring. Over time, only long-necked tortoises would be present in the population.

Natural selection, Darwin argued, was an inevitable outcome of three principles that operated in nature. First, most characteristics of organisms are inherited, or passed from parent to offspring. Although no one, including Darwin and Wallace, knew how this happened at the time, it was a common understanding. Second, more offspring are produced than are able to survive, so resources for survival and reproduction are limited. The capacity for reproduction in all organisms outstrips the availability of resources to support their numbers. Thus, there is competition for those resources in each generation. Both Darwin and Wallace’s understanding of this principle came from reading economist Thomas Malthus' essay that explained this principle in relation to human populations. Third, offspring vary among each other in regard to their characteristics and those variations are inherited. Darwin and Wallace reasoned that offspring with inherited characteristics which allow them to best compete for limited resources will survive and have more offspring than those individuals with variations that are less able to compete. Because characteristics are inherited, these traits will be better represented in the next generation. This will lead to change in populations over generations in a process that Darwin called descent with modification. Ultimately, natural selection leads to greater adaptation of the population to its local environment. It is the only mechanism known for adaptive evolution.

In 1858, Darwin and Wallace ( Figure 18.3 ) presented papers at the Linnean Society in London that discussed the idea of natural selection. The following year Darwin’s book, On the Origin of Species, was published. His book outlined in considerable detail his arguments for evolution by natural selection.

Studies of evolution by natural selection are difficult to conduct, as they require analyses of several generations of the investigated species in order to document the changes pointing to evolutionary change. The Galápagos finches are an excellent example. Peter and Rosemary Grant and their colleagues have studied Galápagos finch populations every year since 1976 and have provided important evidence of natural selection. The Grants found changes from one generation to the next in beak shape distribution with the medium ground finch on the Galápagos island of Daphne Major. The birds have inherited a variation in their bill shape with some having wide deep bills and others having thinner bills. During a period in which rainfall was higher than normal because of an El Niño, there was a lack of large hard seeds of which the large-billed birds ate; however, there was an abundance of the small soft seeds which the small-billed birds ate. Therefore, the small-billed birds were able to survive and reproduce. In the years following this El Niño, the Grants measured beak sizes in the population and found that the average bill size was smaller. Since bill size is an inherited trait, parents with smaller bills had more offspring and the bill evolved into a much smaller size. As conditions improved in 1987 and larger seeds became more available, the trend toward smaller average bill size ceased.

Career Connection

Field biologist.

Many people hike, explore caves, scuba dive, or climb mountains for recreation. People often participate in these activities hoping to see wildlife. Experiencing the outdoors can be incredibly enjoyable and invigorating. What if your job entailed working in the wilderness? Field biologists by definition work outdoors in the “field.” The term field in this case refers to any location outdoors, even under water. A field biologist typically focuses research on a certain species, group of organisms, or a single habitat ( Figure 18.4 ).

One objective of many field biologists includes discovering new, unrecorded species. Not only do such findings expand our understanding of the natural world, but they also lead to important innovations in fields such as medicine and agriculture. Plant and microbial species, in particular, can reveal new medicinal and nutritive knowledge. Other organisms can play key roles in ecosystems or if rare require protection. When discovered, researchers can use these important species as evidence for environmental regulations and laws.

Processes and Patterns of Evolution

Natural selection can only take place if there is variation , or differences, among individuals in a population. Importantly, these differences must have some genetic basis; otherwise, the selection will not lead to change in the next generation. This is critical because nongenetic reasons can cause variation among individuals such as an individual's height because of better nutrition rather than different genes.

Genetic diversity in a population comes from two main mechanisms: mutation and sexual reproduction. Mutation, a change in DNA, is the ultimate source of new alleles, or new genetic variation in any population. The genetic changes that mutation causes can have one of three outcomes on the phenotype. A mutation affects the organism's phenotype in a way that gives it reduced fitness—lower likelihood of survival or fewer offspring. A mutation may produce a phenotype with a beneficial effect on fitness. Many mutations will also have no effect on the phenotype's fitness. We call these neutral mutations. Mutations may also have a whole range of effect sizes on the organism's fitness that expresses them in their phenotype, from a small effect to a great effect. Sexual reproduction also leads to genetic diversity: when two parents reproduce, unique combinations of alleles assemble to produce the unique genotypes and thus phenotypes in each offspring.

We call a heritable trait that helps an organism's survival and reproduction in its present environment an adaptation . Scientists describe groups of organisms adapting to their environment when a genetic variation occurs over time that increases or maintains the population's “fit” to its environment. A platypus's webbed feet are an adaptation for swimming. A snow leopard's thick fur is an adaptation for living in the cold. A cheetah's fast speed is an adaptation for catching prey.

Whether or not a trait is favorable depends on the current environmental conditions. The same traits are not always selected because environmental conditions can change. For example, consider a plant species that grew in a moist climate and did not need to conserve water. Large leaves were selected because they allowed the plant to obtain more energy from the sun. Large leaves require more water to maintain than small leaves, and the moist environment provided favorable conditions to support large leaves. After thousands of years, the climate changed, and the area no longer had excess water. The direction of natural selection shifted so that plants with small leaves were selected because those populations were able to conserve water to survive the new environmental conditions.

The evolution of species has resulted in enormous variation in form and function. Sometimes, evolution gives rise to groups of organisms that become tremendously different from each other. We call two species that evolve in diverse directions from a common point divergent evolution . We can see such divergent evolution in the forms of the reproductive organs of flowering plants which share the same basic anatomies; however, they can look very different as a result of selection in different physical environments and adaptation to different kinds of pollinators ( Figure 18.5 ).

In other cases, similar phenotypes evolve independently in distantly related species. For example, flight has evolved in both bats and insects, and they both have structures we refer to as wings, which are adaptations to flight. However, bat and insect wings have evolved from very different original structures. We call this phenomenon convergent evolution , where similar traits evolve independently in species that do not share a recent common ancestry. The trait in the two species came to be similar in structure and have the same function, flying, but did so separately from each other.

These physical changes occur over enormous time spans and help explain how evolution occurs. Natural selection acts on individual organisms, which can then shape an entire species. Although natural selection may work in a single generation on an individual, it can take thousands or even millions of years for an entire species' genotype to evolve. It is over these large time spans that life on earth has changed and continues to change.

Evidence of Evolution

The evidence for evolution is compelling and extensive. Looking at every level of organization in living systems, biologists see the signature of past and present evolution. Darwin dedicated a large portion of his book, On the Origin of Species , to identifying patterns in nature that were consistent with evolution, and since Darwin, our understanding has become clearer and broader.

Fossils provide solid evidence that organisms from the past are not the same as those today, and fossils show the gradual evolutionary changes over time. Scientists determine the age of fossils and categorize them from all over the world to determine when the organisms lived relative to each other. The resulting fossil record tells the story of the past and shows the evolution of form over millions of years ( Figure 18.6 ). For example, scientists have recovered highly detailed records showing the evolution of humans and horses ( Figure 18.6 ). The whale flipper shares a similar morphology to bird and mammal appendages ( Figure 18.7 ) indicating that these species share a common ancestor.

Anatomy and Embryology

Another type of evidence for evolution is the presence of structures in organisms that share the same basic form. For example, the bones in human, dog, bird, and whale appendages all share the same overall construction ( Figure 18.7 ) resulting from their origin in a common ancestor's appendages. Over time, evolution led to changes in the bones' shapes and sizes in different species, but they have maintained the same overall layout. Scientists call these synonymous parts homologous structures .

Some structures exist in organisms that have no apparent function at all, and appear to be residual parts from a past common ancestor. We call these unused structures without function vestigial structures . Other examples of vestigial structures are wings on flightless birds, leaves on some cacti, and hind leg bones in whales. Not all similarities represent homologous structures. As explained in Determining Evolutionary Relationships , when similar characteristics occur because of environmental constraints and not due to a close evolutionary relationship, it is an analogy or homoplasy. For example, insects use wings to fly like bats and birds, but the wing structure and embryonic origin are completely different. These are analogous structures ( Figure 20.8 ). On the other side, the bird and bat wings are homologous because the bones are inherited from a common ancestor, while the wings themselves are analogous as they evolved independently.

Link to Learning

Watch this video exploring the bones in the human body.

Another piece of evidence of evolution is the convergence of form in organisms that share similar environments. For example, species of unrelated animals, such as the arctic fox and ptarmigan, living in the arctic region have been selected for seasonal white phenotypes during winter to blend with the snow and ice ( Figure 18.8 ). These similarities occur not because of common ancestry, but because of similar selection pressures—the benefits of predators not seeing them.

Embryology, the study of the anatomy of an organism's development to its adult form, also provides evidence of relatedness between now widely divergent groups of organisms. Mutational tweaking in the embryo can have such magnified consequences in the adult that embryo formation tends to be conserved. As a result, structures that are absent in some groups often appear in their embryonic forms and disappear when they reach the adult or juvenile form. For example, all vertebrate embryos, including humans, exhibit gill slits and tails at some point in their early development. These disappear in the adults of terrestrial groups but adult forms of aquatic groups such as fish and some amphibians maintain them. Great ape embryos, including humans, have a tail structure during their development that they lose when they are born.

Biogeography

The geographic distribution of organisms on the planet follows patterns that we can explain best by evolution in conjunction with tectonic plate movement over geological time. Broad groups that evolved before the supercontinent Pangaea broke up (about 200 million years ago) are distributed worldwide. Groups that evolved since the breakup appear uniquely in regions of the planet, such as the unique flora and fauna of northern continents that formed from the supercontinent Laurasia and of the southern continents that formed from the supercontinent Gondwana. The presence of members of the plant family Proteaceae in Australia, southern Africa, and South America indicates that their ancestors were predominant on the supercontinent Gondwana prior to its breaking up.

Marsupial diversification in Australia and the absence of other mammals reflect Australia’s long isolation. Australia has an abundance of endemic species—species found nowhere else—which is typical of islands whose isolation by expanses of water prevents species from migrating. Over time, these species diverge evolutionarily into new species that look very different from their ancestors that may exist on the mainland. Australia's marsupials, the Galápagos' finches, and many species on the Hawaiian Islands are all unique to their one point of origin, yet they display distant relationships to ancestral species on mainlands.

Molecular Biology

Like anatomical structures, the molecular structures of life reflect descent with modification. DNA's universality reflects evidence of a common ancestor for all of life. Fundamental divisions in life between the genetic code, DNA replication, and expression are reflected in major structural differences in otherwise conservative structures such as ribosome components and membrane structures. In general, the relatedness of groups of organisms is reflected in the similarity of their DNA sequences—exactly the pattern that we would expect from descent and diversification from a common ancestor.

DNA sequences have also shed light on some of the mechanisms of evolution. For example, it is clear that the evolution of new functions for proteins commonly occurs after gene duplication events that allow freely modifying one copy by mutation, selection, or drift (changes in a population’s gene pool resulting from chance), while the second copy continues to produce a functional protein.

Misconceptions of Evolution

Although the theory of evolution generated some controversy when Darwin first proposed it, biologists almost universally accepted it, particularly younger biologists, within 20 years after publication of On the Origin of Species . Nevertheless, the theory of evolution is a difficult concept and misconceptions about how it works abound.

This site addresses some of the main misconceptions associated with the theory of evolution.

Evolution Is Just a Theory

Critics of the theory of evolution dismiss its importance by purposefully confounding the everyday usage of the word “theory” with the way scientists use the word. In science, we understand a “theory” to be a body of thoroughly tested and verified explanations for a set of observations of the natural world. Scientists have a theory of the atom, a theory of gravity, and the theory of relativity, each which describes understood facts about the world. In the same way, the theory of evolution describes facts about the living world. As such, a theory in science has survived significant efforts to discredit it by scientists. In contrast, a “theory” in common vernacular is a word meaning a guess or suggested explanation. This meaning is more akin to the scientific concept of “hypothesis.” When critics of evolution say it is “just a theory,” they are implying that there is little evidence supporting it and that it is still in the process of rigorous testing. This is a mischaracterization.

Individuals Evolve

Evolution is the change in a population's genetic composition over time, specifically over generations, resulting from differential reproduction of individuals with certain alleles. Individuals do change over their lifetime, obviously, but this is development and involves changes programmed by the set of genes the individual acquired at birth in coordination with the individual’s environment. When thinking about the evolution of a characteristic, it is probably best to think about the change of the average value of the characteristic in the population over time. For example, when natural selection leads to bill-size change in medium ground finches in the Galápagos, this does not mean that individual bills on the finches are changing. If one measures the average bill size among all individuals in the population at one time and then measures them in the population several years later, this average value will be different as a result of evolution. Although some individuals may survive from the first time to the second, they will still have the same bill size; however, there will be many new individuals who contribute to the shift in average bill size.

Evolution Explains the Origin of Life

It is a common misunderstanding that evolution includes an explanation of life’s origins. Some of the theory’s critics believe that it cannot explain the origin of life. The theory does not try to explain the origin of life. The theory of evolution explains how populations change over time and how life diversifies the origin of species. It does not shed light on the beginnings of life including the origins of the first cells, which define life. Importantly, biologists believe that the presence of life on Earth precludes the possibility that the events that led to life on Earth can repeat themselves because the intermediate stages would immediately become food for existing living things.

However, once a mechanism of inheritance was in place in the form of a molecule like DNA either within a cell or pre-cell, these entities would be subject to the principle of natural selection. More effective reproducers would increase in frequency at the expense of inefficient reproducers. While evolution does not explain the origin of life, it may have something to say about some of the processes operating once pre-living entities acquired certain properties.

Organisms Evolve on Purpose

Statements such as “organisms evolve in response to a change in an environment” are quite common, but such statements can lead to two types of misunderstandings. First, do not interpret the statement to mean that individual organisms evolve. The statement is shorthand for “a population evolves in response to a changing environment.” However, a second misunderstanding may arise by interpreting the statement to mean that the evolution is somehow intentional. A changed environment results in some individuals in the population, those with particular phenotypes, benefiting and therefore producing proportionately more offspring than other phenotypes. This results in change in the population if the characteristics are genetically determined.

It is also important to understand that the variation that natural selection works on is already in a population and does not arise in response to an environmental change. For example, applying antibiotics to a population of bacteria will, over time, select a population of bacteria that are resistant to antibiotics. The resistance, which a gene causes, did not arise by mutation because of applying the antibiotic. The gene for resistance was already present in the bacteria's gene pool, likely at a low frequency. The antibiotic, which kills the bacterial cells without the resistance gene, strongly selects individuals that are resistant, since these would be the only ones that survived and divided. Experiments have demonstrated that mutations for antibiotic resistance do not arise as a result of antibiotic application.

In a larger sense, evolution is not goal directed. Species do not become “better” over time. They simply track their changing environment with adaptations that maximize their reproduction in a particular environment at a particular time. Evolution has no goal of making faster, bigger, more complex, or even smarter species, despite the commonness of this kind of language in popular discourse. What characteristics evolve in a species are a function of the variation present and the environment, both of which are constantly changing in a nondirectional way. A trait that fits in one environment at one time may well be fatal at some point in the future. This holds equally well for insect and human species.

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ENCYCLOPEDIC ENTRY

Theory of evolution.

The theory of evolution is a shortened form of the term “theory of evolution by natural selection,” which was proposed by Charles Darwin and Alfred Russel Wallace in the nineteenth century.

Biology, Ecology, Earth Science, Geology, Geography, Physical Geography

Young Charles Darwin

Painting of a young Charles Darwin

Photograph by James L. Stanfield

Ideas aimed at explaining how organisms change, or evolve, over time date back to Anaximander of Miletus, a Greek philosopher who lived in the 500s B.C.E. Noting that human babies are born helpless, Anaximander speculated that humans must have descended from some other type of creature whose young could survive without any help. He concluded that those ancestors must be fish, since fish hatch from eggs and immediately begin living with no help from their parents. From this reasoning, he proposed that all life began in the sea.

Anaximander was correct; humans can indeed trace our ancestry back to fish. His idea, however, was not a theory in the scientific meaning of the word, because it could not be subjected to testing that might support it or prove it wrong. In science, the word “ theory ” indicates a very high level of certainty. Scientists talk about evolution as a theory , for instance, just as they talk about Einstein’s explanation of gravity as a theory .

A theory is an idea about how something in nature works that has gone through rigorous testing through observations and experiments designed to prove the idea right or wrong. When it comes to the evolution of life, various philosophers and scientists, including an eighteenth-century English doctor named Erasmus Darwin, proposed different aspects of what later would become evolutionary theory. But evolution did not reach the status of being a scientific theory until Darwin’s grandson, the more famous Charles Darwin, published his famous book On the Origin of Species . Darwin and a scientific contemporary of his, Alfred Russel Wallace, proposed that evolution occurs because of a phenomenon called natural selection .

In the theory of natural selection, organisms produce more offspring than are able to survive in their environment. Those that are better physically equipped to survive, grow to maturity, and reproduce. Those that are lacking in such fitness, on the other hand, either do not reach an age when they can reproduce or produce fewer offspring than their counterparts. Natural selection is sometimes summed up as “survival of the fittest” because the “fittest” organisms—those most suited to their environment—are the ones that reproduce most successfully, and are most likely to pass on their traits to the next generation.

This means that if an environment changes, the traits that enhance survival in that environment will also gradually change, or evolve. Natural selection was such a powerful idea in explaining the evolution of life that it became established as a scientific theory . Biologists have since observed numerous examples of natural selection influencing evolution . Today, it is known to be just one of several mechanisms by which life evolves. For example, a phenomenon known as genetic drift can also cause species to evolve. In genetic drift , some organisms —purely by chance—produce more offspring than would be expected. Those organisms are not necessarily the fittest of their species, but it is their genes that get passed on to the next generation.

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Essay on Human Evolution: Top 6 Essays | Biology

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Here is a compilation of essays on ‘Human Evolution’ for class 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Human Evolution’ especially written for school and college students.

Essay on Human Evolution

Essay Contents:

• Essay on the Models of Human Evolution

Essay # 1.   Introduction to Human Evolution:

Evolution as a process is composed of two parts:

1. An organism reproducing mechanism that provides variable organisms. Changes to the organism are largely random and effect future generations. They are made without regard to consequences to the organism.

2. A changing environment which screens organism changes. The environment provides stress on the variable organisms that selectively allows, through competition, certain changes to become dominant and certain others to be eliminated, without consideration for the future of the mechanism.

That same process provides mechanism (organism) disintegration if a strong screening environment is not present. Evolution is a two-way process which does not always work to the long term advantage of the organism and in fact often becomes quite deadly to a given species and thereby eradicates it.

The evolutionary process is bidirectional in its effect. It may, depending on the environment, either improve a given characteristic or decay it. Since the first step in the process is largely random and most organisms are quite complex, almost all of the variations are harmful.

A characteristic of a species advances if the environment is harsh, since most harmful variations to that characteristic will be eliminated through death and suffering at a rapid rate, leaving only the inconsequential and helpful changes in the lineage.

If the environment is benign with respect to the capability of the species then the harmful changes are not eliminated and the species will degenerate to a point of balance with the environment.

Human evolution is the part of biological evolution concerning the emergence of Homo sapiens as a distinct species from other hominans, great apes and placental mammals. It is the subject of a broad scientific inquiry that seeks to understand and describe how this change occurred.

Mammals developed from primitive mammal-like reptiles during the Triassic Period, some 200-245 million years ago. After the terminal Cretaceous extinction (65 million years ago) eliminated the dinosaurs, mammals as one of the surviving groups, underwent an adaptive radiation during the Tertiary Period.

The major orders of mammals developed at this time, including the Primates to which humans belong. Other primates include the tarsiers, lemurs, gibbons, monkeys, and apes. Although we have significant differences from other primates, we share an evolutionary history that includes traits such as opposable thumbs, stereoscopic vision, larger brains, and nails replacing claws.

Primates are relatively unspecialized mammals- they have no wings, still have all four limbs, cannot run very fast, have generally weak teeth, and lack armor or thick protective hides. However, the combination of primate adaptations that include larger brains, tool use, social structure, stereoscopic color vision, highly developed forelimbs and hands, versatile teeth, and upright posture, place them among the most advanced mammals.

Approximately 20 million years ago central and east Africa was densely forested. Climatic changes resulting from plate tectonic movements and episodes of global cooling about 15 million years ago caused a replacement of the forest by a drier-adapted savanna mixed with open areas of forest. During the course of hominid evolution, periodic climate changes would trigger bursts of evolution and/or extinction.

Primates have modifications to their ulna and radius (bones of the lower arm) allowing them to turn their hand without turning their elbow. Many primates can also swivel or turn their arms at the shoulder. These two adaptations offer advantages to life in the trees.

Primates have five digits on their forelimbs. They are able to grasp objects with their forelimbs in what is known as a prehensile movement. A second modification makes one of the digits opposable, allowing the tips of the fingers and thumb to touch.

Placement of the eyes on the front of the head increases depth perception, an advantageous trait in tree-dwelling primates. Changes in the location of rods and cones in the eye adapted primates for color vision as well as peripheral vision in dim light.

Upright posture allows a primate to view its surroundings as well as to use its hands for some other task. Hominids, the lineage leading to humans, had changes in the shape and size of their pelvis, femur, and knees that allowed bipedalism (walking on two legs). The change from quadruped to biped happened in stages, culminating in humans, who can walk or run on two legs.

Several trends of primate evolution are evident in the teeth and jaw. First, change in the geometry of the jaw reduced the snout into a flat face. Second, changes in tooth arrangement and numbers increased the efficiency of those teeth for grinding food. Third, about 1.5 million years ago our diet changed from fruits and vegetables to include meat.

Essay # 2. Origin of Apes and Hominids:

The fossil record indicates primates evolved about approximately 30 million years ago in Africa. One branch of primates evolved into the Old and New World Monkeys, the other into the hominoids (the line of descent common to both apes and man).

Fossil hominoids occur in Africa during the Miocene epoch of the Tertiary period. They gave rise to an array of species in response to major climate fluxes in their habitats. However, the nature of those habitats leads to an obscuration of the line that leads to humans (the hominids).

Until a few years ago, the ramapiths were thought to have given rise to the hominids. We now consider ramapiths ancestral to the orangutang. The hominid line arose from some as-yet-unknown ancestor. Lacking fossil evidence, biochemical and DNA evidence suggests a split of the hominid from hominoid line about 6 to 8 million years ago.

Australopithecus afarensis, the first of the human-like hominids we know of, first appeared about 3.6-4 million years ago. This species had a combination of human (bipedalism) and apelike features (short legs and relatively long arms). The arm bones were curved like chimps, but the elbows were more human-like. Scientists speculate that A. afarensis spent some time climbing trees, as well as on the ground.

Australopithecus ramidus is an older species, about 4.4 million years, and is generally considered more anatomically primitive than A. afarensis. The relationship between the two species remains to be solved.

History of Man:

I. Ardipithicus ramidus- 5 to 4 million years ago

II. Australopithecus anamensis- 4.2 to 3.9 million years ago

III. Australopithecus afarensis- 4 to 2.7 million years ago

IV. Australopithecus africanus- 3 to 2 million years ago

V. Australopithecus robustus- 2.2 to 1.6 million years ago

VI. Homo habilis- 2.2 to 1.6 million years ago

VII. Homo erectus- 2.0 to 0.4 million years ago

VIII. Homo sapiens archaic- 400 to 200 thousand years ago

IX. Homo sapiens neandertalensis- 200 to 30 thousand years ago

X. Homo sapiens sapiens- 200 thousand years ago to present.

The role of A. afarensis as the stem from which the other hominids arose is in some dispute. About 2 million years ago, after a long million year period of little change, as many as six hominid species evolved in response to climate changes associated with the beginning of the Ice Age.

Two groups developed- the australopithecines, generally smaller brained and not users of tools; and the line that led to genus Homo, larger brained and makers and users of tools. The australopithecines died out 1 million years ago; Homo, despite their best efforts (atomic weapons, pollution) is still here!

With an incomplete fossil record, australopithecines, at least the smaller form, A. africanus, was thought ancestral to Homo. Recent discoveries however have caused a reevaluation of that hypothesis. One pattern is sure, human traits evolved at different rates and at different times, in a mosaic- some features (skeletal, dietary) establishing themselves quickly, others developing later (tool making, language, use of fire).

A cluster of species developed about 2-2.5 million years ago in Africa. Homo had a larger brain and a differently shaped skull and teeth than the australopithecines. About 1.8 million years ago, early Homo gave rise to Homo erectus, the species thought to have been ancestral to our own.

Soon after its origin (1.8 million but probably older than 2 million years ago) in Africa, Homo erectus appears to have migrated out of Africa and into Europe and Asia. Homo erectus differed from early species of Homo in having a larger brain size, flatter face, and prominent brow ridges. Homo erectus is similar to modern humans in size, but has some differences in the shape of the skull, a receding chin, brow ridges, and differences in teeth.

Homo erectus was the first hominid to:

1. Provide evidence the social and cultural aspects of human evolution.

2. Leave Africa (living in Africa, Europe, and Asia).

3. Use fire.

4. Have social structures for food gathering.

5. Utilize permanent settlements.

6. Provide a prolonged period of growth and maturation after birth Between 100,000 and 500,000 years ago, the world population of an estimated 1 million Homo erectus disappeared, replaced by a new species, Homo sapiens. How, when and where this new species arose and how it replaced its predecessor remain in doubt. Answering those questions has become a multidisciplinary task.

Two hypotheses differ on how and where Homo sapiens originated:

1. The Out-of-Africa Hypothesis proposes that some H. erectus remained in Africa and continued to evolve into H. sapiens, and left Africa about 100,000-200,000 years ago. From a single source, H. sapiens replaced all populations of H. erectus.

Human populations today are thus all descended from a single speciation event in Africa and should display a high degree of genetic similarity. Support for this hypothesis comes from DNA studies of mitochondria- since African populations display the greatest diversity of mitochondrial DNA, modern humans have been in Africa longer than they have been elsewhere. Calculations suggest all modern humans are descended from a population of African H. sapiens numbering as few as 10,000.

2. The Regional Continuity Hypothesis suggests that regional populations of H. erectus evolved into H. sapiens through interbreeding between the various populations. Evidence from the fossil record and genetic studies supports this idea.

Scientists can often use the same “evidence” to support contrasting hypotheses depending on which evidence (fossils or molecular clock/ DNA studies) one gives more weight to. The accuracy of the molecular clock, so key to the out-of-Africa hypothesis, has recently been questioned.

Recent studies on the Y-chromosome seem to weaken the regional continuity hypothesis by indicating a single point-of-origin for our species some 270,000 years ago. Continued study will no doubt reveal new evidence and undoubtedly new hypotheses will arise. It is a task for all of us to weigh the evidence critically and reach a supportable conclusion, whether we are scientists or not.

Essay # 3. H istory of the Primates:

Before Homo:

The evolutionary history of the primates can be traced back for some 85 million years, as one of the oldest of all surviving placental mammal groups. Most paleontologists consider that primates share a common ancestor with the bats, another extremely ancient lineage, and that this ancestor probably lived during the late Cretaceous, together with the last dinosaurs. The oldest known primates come from North America, but they were widespread in Eurasia and Africa as well, during the tropical conditions of the Paleocene and Eocene.

With the beginning of modern climates, marked by the formation of the first Antarctic ice in the early Oligocene around 40 million years ago, primates went extinct everywhere but Africa and southern Asia. One such primate from this time was Notharctus.

Fossil evidence found in Germany 20 years ago was determined to be about 16.5 million years old, some 1.5 million years older than similar species from East Africa. It suggests that the primate lineage of the great apes first appeared in Eurasia and not Africa.

The discoveries suggest that the early ancestors of the hominids (the family of great apes and humans) migrated to Eurasia from Africa about 17 million years ago, just before these two continents were cut off from each other by an expansion of the Mediterranean Sea. These primates flourished in Eurasia and that their lineage leading to the African apes and humans —Dryopithecus—migrated south from Europe or Western Asia into Africa.

The surviving tropical population, which is seen most completely in the upper Eocene and lowermost Oligocene fossil beds of the Fayum depression southwest of Cairo, gave rise to all living primates—lemurs of Madagascar, lorises of Southeast Asia, galagos or “bush babies” of Africa, and the anthropoids; platyrrhines or New World monkeys, and catarrhines or Old World monkeys and the great apes and humans.

The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Kenya rift valley, dated to 24 mya (millions of years before present). Its ancestry is generally thought to be close to such genera as Aegyptopithecus, Propliopithecus, and Parapithecus from the Fayum, at around 35 mya.

There are no fossils from the intervening 11 million years. No near ancestor to South American platyrrhines, whose fossil record begins at around 30 mya, can be identified among the North African fossil species, and possibly lies in other forms that lived in West Africa that were caught up in the still-mysterious transatlantic sweepstakes that sent primates, rodents, boa constrictors, and cichlid fishes from Africa to South America sometime in the Oligocene.

In the early Miocene, after 22 mya, many kinds of arboreally adapted primitive catarrhines from East Africa suggest a long history of prior diversification. Because the fossils at 20 mya include fragments attributed to Victoriapithecus, the earliest cercopithecoid, the other forms are (by default) grouped as hominoids, without clear evidence as to which are closest to living apes and humans.

Among the presently recognised genera in this group, which ranges up to 13 mya, we find Proconsul, Rangwapithecus, Dendropithecus, Limnopithecus, Nacholapithecus, Equatorius, Nyanzapithecus, Afropithecus, Heliopithecus, and Kenyapithecus, all from East Africa.

The presence of other generalised non-cercopithecids of middle Miocene age from sites far distant—Otavipithecus from cave deposits in Namibia, and Pierolapithecus and Dryopithecus from France, Spain and Austria—is evidence of a wide diversity of forms across Africa and the Mediterranean basin during the relatively warm and equable climatic regimes of the early and middle Miocene.

The youngest of the Miocene hominoids, Oreopithecus, is from 9 mya coal beds in Italy.

Molecular evidence indicates that the lineage of gibbons (family Hylobatidae) became distinct between 18 and 12 Ma, and that of orangutans (subfamily Ponginae) at about 12 Ma; we have no fossils that clearly document the ancestry of gibbons, which may have originated in a so far unknown South East Asian hominid population, but fossil proto-orangutans may be represented by Ramapithecus from India and Griphopithecus from Turkey, dated to around 10 Ma.

It has been suggested that species close to last common ancestors of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece.

Molecular evidence suggests that between 8 and 4 mya, first the gorillas, and then the chimpanzee (genus Pan) split off from the line leading to the humans; human DNA is 98.4 percent identical to the DNA of chimpanzees. We have no fossil record, however, of either group of African great apes, possibly because bones do not fossilize in rain forest environments.

Hominines, however, seem to have been one of the mammal groups (as well as antelopes, hyenas, dogs, pigs, elephants, and horses) that adapted to the open grasslands as soon as this biome appeared, due to increasingly seasonal climates, about 8 mya, and their fossils are relatively well known.

The earliest are Sahelanthropus tchadensis (7- 6 mya) and Orrorin tugenensis (6 mya), followed by:

1. Ardipithecus (5.5-4.4 mya), with species Ar. kadabba and Ar. Ramidus.

2. Australopithecus (4-2 mya), with species Au. anamensis, Au. afarensis, Au. africanus, Au. bahrelghazali, and Au. Garhi.

3. Kenyanthropus (3-2.7 mya), with species Kenyanthropus platyops.

4. Paranthropus (3-1.2 mya), with species P. aethiopicus, P. boisei, and P. robustus.

5. Homo (2 mya-present), with species Homo habilis, Homo rudolfensis, Homo ergaster, Homo georgicus, Homo antecessor, Homo cepranensis, Homo erectus, Homo heidelbergensis, Homo rhodesiensis, Homo sapiens neanderthalensis, Homo sapiens idaltu, Archaic Homo sapiens, Homo floresiensis.

Essay # 4. Genus of Homo:

The word homo is Latin for “human”, chosen originally by Carolus Linnaeus in his classification system. It is often translated as “man”, although this can lead to confusion, given that the English word “man” can be generic like homo, but can also specifically refer to males. Latin for “man” in the gender-specific sense is vir (pronounced weer), cognate with “virile” and “werewolf”. The word “human” is from humanus, the adjectival form of homo.

In modern taxonomy, Homo sapiens are the only extant species of its genus, Homo. Likewise, the ongoing study of the origins of Homo sapiens often demonstrates that there were other Homo species, all of which are now extinct. While some of these other species might have been ancestors of H. sapiens, many were likely our “cousins”, having speciated away from our ancestral line.

There is not yet a consensus as to which of these groups should count as separate species and which as subspecies of another species. In some cases this is due to the paucity of fossils, in other cases it is due to the slight differences used to classify species in the Homo genus. The Sahara pump theory provides an explanation of the early variation in the genus Homo.

i. Homo Habilis:

H. habilis lived from about 2.4 to 1.4 million years ago (mya). H. habilis, the first species of the genus Homo, evolved in South and East Africa in the late Pliocene or early Pleistocene, 2.5-2 mya, when it diverged from the Australopithecines.

H. habilis had smaller molars and larger brains than the Australopithecines, and made tools from stone and perhaps animal bones. One of the first known hominids, it was nicknamed ‘handy man’ by its discoverer, Louis Leakey. Some scientists have proposed moving this species out of Homo and into Australopithecus.

ii. Homo Rudolfensis and Homo Georgicus:

These are proposed species names for fossils from about 1.9 -1.6 mya, the relation of which with H. habilis is not yet clear. H. rudolfensis refers to a single, incomplete skull from Kenya. Scientists have suggested that this was just another habilis, but this has not been confirmed.

H. georgicus, from Georgia, may be an intermediate form between H. habilis and H. erectus, or a sub-species of H. erectus.

iii. Homo Ergaster and Homo Erectus:

The first fossils of Homo erectus were discovered by Dutch physician Eugene Dubois in 1891 on the Indonesian island of Java. He originally gave the material the name Pithecanthropus erectus based on its morphology that he considered to be intermediate between that of humans and apes.

H. erectus lived from about 1.8 mya to 70,000 years ago. Often the early phase, from 1.8 to 1.25 mya, is considered to be a separate species, H. ergaster, or it is seen as a subspecies of erectus, Homo erectus ergaster.

In the Early Pleistocene, 1.5-1 mya, in Africa, Asia, and Europe, presumably, Homo habilis evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, H. erectus. In addition H. erectus was the first human ancestor to walk truly upright.

This was made possible by the evolution of locking knees and a different location of the foramen magnum (the hole in the skull where the spine enters). They may have used fire to cook their meat.

A famous example of Homo erectus is Peking Man; others were found in Asia (notably in Indonesia), Africa, and Europe. Many paleoanthropologists are now using the term Homo ergaster for the non-Asian forms of this group, and reserving H. erectus only for those fossils found in the Asian region and meeting certain skeletal and dental requirements which differ slightly from ergaster.

iv. Homo Cepranensis and Homo Antecessor:

These are proposed as species that may be intermediate between H. erectus and H. heidelbergensis.

H. cepranensis refers to a single skull cap from Italy, estimated to be about 800,000 years old.

H. antecessor is known from fossils from Spain and England that are 800,000-500,000 years old.

v. Homo Heidelbergensis:

H. heidelbergensis (Heidelberg Man) lived from about 800,000 to about 300,000 years ago. Also proposed as Homo sapiens heidelbergensis or Homo sapiens paleohungaricus.

vi. Homo Neanderthalensis:

H. neanderthalensis lived from about 250,000 to as recent as 30,000 years ago. Also proposed as Homo sapiens neanderthalensis- there is ongoing debate over whether the ‘Neanderthal Man’ was a separate species, Homo neanderthalensis, or a subspecies of H. sapiens.

While the debate remains unsettled, evidence from mitochondrial DNA and Y-chromosomal DNA sequencing indicates that little or no gene flow occurred between H. neanderthalensis and H. sapiens, and, therefore, the two were separate species.

vii. Homo Rhodesiensis, and the Gawis Cranium:

H. rhodesiensis, estimated to be 300,000-125,000 years old, most current experts believe Rhodesian Man to be within the group of Homo heidelbergensis though other designations such as Archaic Homo sapiens and Homo sapiens rhodesiensis have also been proposed.

In February 2006 a fossil, the Gawis cranium, was found which might possibly be a species intermediate between H. erectus and H. sapiens or one of many evolutionary dead ends. The skull from Gawis, Ethiopia, is believed to be 500,000-250,000 years old.

Only summary details are known, and no peer reviewed studies have been released by the finding team. Gawis man’s facial features suggest its being either an intermediate species or an example of a “Bodo man” female.

viii. Homo Sapiens:

H. sapiens (“sapiens” means wise or intelligent) has lived from about 250,000 years ago to the present. Between 400,000 years ago and the second interglacial period in the Middle Pleistocene, around 250,000 years ago, the trend in cranial expansion and the elaboration of stone tool technologies developed, providing evidence for a transition from H. erectus to H. sapiens.

The direct evidence suggests that there was a migration of H. erectus out of Africa, then a further speciation of H. sapiens from H. erectus in Africa (there is little evidence that this speciation occurred elsewhere). Then a subsequent migration within and out of Africa eventually replaced the earlier dispersed H. erectus.

This migration and origin theory is usually referred to as the single- origin theory. However, the current evidence does not preclude multiregional speciation, either. This is a hotly debated area in paleoanthropology.

Current research has established that human beings are genetically highly homogenous, that is the DNA of individuals is more alike than usual for most species, which may have resulted from their relatively recent evolution or the Toba catastrophe. Distinctive genetic characteristics have arisen, however, primarily as the result of small groups of people moving into new environmental circumstances.

These adapted traits are a very small component of the Homo sapiens genome and include such outward “racial” characteristics as skin color and nose form in addition to internal characteristics such as the ability to breathe more efficiently in high altitudes.

H. sapiens idaltu, from Ethiopia, lived from about 160,000 years ago (proposed subspecies). It is the oldest known anatomically modern human.

ix. Homo Floresiensis :

H. floresiensis, which lived about 100,000-12,000 years ago has been nicknamed hobbit for its small size, possibly a result of insular dwarfism. H. floresiensis is intriguing both for its size and its age, being a concrete example of a recent species of the genus Homo that exhibits derived traits not shared with modern humans.

In other words, H. floresiensis share a common ancestor with modern humans, but split from the modern human lineage and followed a distinct evolutionary path. The main find was a skeleton believed to be a woman of about 30 years of age. Found in 2003 it has been dated to approximately 18,000 years old. Her brain size was only 380 cm 3 (which can be considered small even for a chimpanzee). She was only 1 meter in height.

However, there is an ongoing debate over whether H. floresiensis is indeed a separate species. Some scientists presently believe that H. floresiensis was a modern H. sapiens suffering from pathological dwarfism.

Use of Tools:

Using tools has been interpreted as a sign of intelligence, and it has been theorized that tool use may have stimulated certain aspects of human evolution—most notably the continued expansion of the human brain. Paleontology has yet to explain the expansion of this organ over millions of years despite being extremely demanding in terms of energy consumption.

The brain of a modern human consumes about 20 Watts (400 kilocalories per day), which is one fifth of the energy consumption of a human body. Increased tool use would allow for hunting and consuming meat, which is more energy-rich than plants. Researchers have suggested that early hominids were thus under evolutionary pressure to increase their capacity to create and use tools.

Precisely when early humans started to use tools is difficult to determine, because the more primitive these tools are (for example, sharp-edged stones) the more difficult it is to decide whether they are natural objects or human artifacts.

Stone Tools:

Stone tools are first attested around 2.6 million years ago, when H. habilis in Eastern Africa used so-called pebble tools, choppers made out of round pebbles that had been split by simple strikes.

This marks the beginning of the Paleolithic, or Old Stone Age; its end is taken to be the end of the last Ice Age, around 10,000 years ago. The Paleolithic is subdivided into the Lower Paleolithic (Early Stone Age, ending around 350,000-300,000 years ago), the Middle Paleolithic (Middle Stone Age, until 50,000-30,000 years ago), and the Upper Paleolithic.

The period from 700,000-300,000 years ago is also known as the Acheulean, when H. ergaster (or erectus) made large stone hand-axes out of flint and quartzite, at first quite rough (Early Acheulian), later “retouched” by additional, more subtle strikes at the sides of the flakes.

After 350,000 BP (Before Present) the more refined so-called Levallois technique was developed. It consisted of a series of consecutive strikes, by which scrapers, slicers (“racloirs”), needles, and flattened needles were made. Finally, after about 50,000 BP, ever more refined and specialised flint tools were made by the Neanderthals and the immigrant Cro-Magnons (knives, blades, skimmers). In this period they also started to make tools out of bone.

Essay # 5. Evolution of Neanderthals :

Archaic H. sapiens lived from 500,000 to 30,000 years ago and combined features of H. sapiens with those of H. erectus. The Neanderthals, considered in this group, lived in Europe and western Asia between 100,000 and 30,000 years ago before their disappearance.

Neanderthals were larger-brained than modern humans, had a sloping forehead, prominent brow ridges and a receding chin. They had a very prominent nose and ranged in height from 5 foot 2 inches (average female) to 5 foot 6 inches (average male).

Despite their image as brutish simpletons, Neanderthals were the first humans to bury their dead with artifacts, indicating abstract thought, perhaps a belief in an after-life. They lived in free-standing settlements, as well as caves. Neanderthal tools were more sophisticated than H. erectus’ tools, employing handles to gain extra leverage.

Did Neanderthals evolve gradually into modern humans, or were they replaced by modern forms originating from a single population? The answer to that depends on the answer to the question of the origin of H. sapiens from H. erectus. The out-of-Africa hypothesis suggests Neanderthals were a separate species (H. neandertalensis) replaced as modern humans (H. sapiens) spread from Africa. The regional continuity hypothesis suggests Neanderthals were a subspecies (H. sapiens neandertalensis) that evolved into modern humans (H. sapiens sapiens).

Agriculture and Migrations :

Since the evolution of H. erectus, migrations have been a fact of human existence, helping to spread genetic diversity as well as technological innovation. The most recent innovations have not been physical, but rather cultural.

The Neolithic transition, about 10,000 years ago, involved the change from hunter-gatherer societies to agricultural ones based on cultivation of plants and domesticated animals. Evidence suggests this began in the Middle East and spread outward via migrations. Genetic studies suggest agriculture spread by the migration of farmers into hunter-gatherer societies. This would produce a genetic blurring as the farmers interbred with the indigenous peoples, a pattern supported by genetics.

Most anthropologists agree that the New World was populated by a series of three migrations over the temporary land connection between Asia and North America. The Immigrants spread southward, eventually reaching Tierra del Fuego in the southernmost part of South America.

Anthropological and linguistic studies find three groups of peoples:

1. The Amerinds, who spread across North and South America.

2. The Na-Denes, who occupied the northwestern region of North America.

3. The Eskaleuts, Eskimo and Aleut peoples who live in the far north.

Mitochondrial DNA studies find four distinct groups descended from peoples of Siberia. Amerind mtDNA suggests two waves of migration (one perhaps as old as 21-42 thousand years ago). The genetic model confirms the accepted ideas about human migration into the Americas and suggests a possible fourth wave.

Essay # 6. Models of Human Evolution:

Today, all humans are classified as belonging to the species Homo sapiens sapiens. However, this is not the first species of hominids- the first species of genus Homo, Homo habilis evolved in East Africa at least 2 million years ago, and members of this species populated different parts of Africa in a relatively short time.

Homo erectus evolved more than 1.8 million years ago, and by 1.5 million years ago had spread throughout the Old World. Virtually all physical anthropologists agree that Homo sapiens evolved out of Homo erectus.

Anthropologists have been divided as to whether Homo sapiens evolved as one interconnected species from H. erectus (called the Multiregional Model, or the Regional Continuity Model), or evolved only in East Africa, and then migrated out of Africa and replaced H. erectus populations throughout the Old World (called the Out of Africa Model or the Complete Replacement Model).

Anthropologists continue to debate both possibilities, and the evidence is technically ambiguous as to which model is correct, although most anthropologists currently favor the Out of Africa model.

Multiregional Model :

Advocates of the Multiregional model, primarily Milford Wolpoff and his followers, have argued that the simultaneous evolution of H. sapiens in different parts of Europe and Asia would have been possible if there was a degree of gene flow between archaic populations.

Similarities of morphological features between archaic European and Chinese populations and modern H. sapiens from the same regions, Wolpoff argues, support a regional continuity only possible within the Multiregional model. Wolpoff and others further argue that this model is consistent with clonal patterns of phenotypic variation.

Out of Africa Model :

According to the Out of Africa Model, developed by Christopher Stringer and Peter Andrews, modern H. sapiens evolved in Africa 200,000 years ago. Homo sapiens began migrating from Africa between 70,000 – 50,000 years ago and would eventually replace existing hominid species in Europe and Asia.

The Out of Africa Model has gained support by recent research using mitochondrial DNA (mtDNA). After analysing genealogy trees constructed using 133 types of mtDNA, they concluded that all were descended from a woman from Africa, dubbed Mitochondrial Eve.

A variation on this model involves the Southern dispersal theory, which has gained support in recent years from genetic, linguistic and archaeological evidence. In this theory, there was a coastal dispersal of modern humans from the Horn of Africa around 70,000 years ago. This group helped to populate Southeast Asia and Oceania, explaining the discovery of early human sites in these areas much earlier than those in the Levant.

A second wave of humans dispersed across the Sinai peninsula into Asia, resulting in the bulk of human population for Eurasia. This second group possessed a more sophisticated tool technology and was less dependent on coastal food sources than the original group. Much of the evidence for the first group’s expansion would have been destroyed by the rising sea levels at the end of the Holocene era.

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evolution , theory in biology postulating that the various types of plants, animals, and other living things on Earth have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations. The theory of evolution is one of the fundamental keystones of modern biological theory.

The diversity of the living world is staggering. More than 2 million existing species of organisms have been named and described; many more remain to be discovered—from 10 million to 30 million, according to some estimates. What is impressive is not just the numbers but also the incredible heterogeneity in size, shape, and way of life —from lowly bacteria , measuring less than a thousandth of a millimetre in diameter, to stately sequoias, rising 100 metres (300 feet) above the ground and weighing several thousand tons; from bacteria living in hot springs at temperatures near the boiling point of water to fungi and algae thriving on the ice masses of Antarctica and in saline pools at −23 °C (−9 °F); and from giant tube worm s discovered living near hydrothermal vents on the dark ocean floor to spider s and larkspur plants existing on the slopes of Mount Everest more than 6,000 metres (19,700 feet) above sea level .

The virtually infinite variations on life are the fruit of the evolutionary process. All living creatures are related by descent from common ancestors. Humans and other mammals descend from shrewlike creatures that lived more than 150 million years ago; mammals, birds, reptiles, amphibians, and fishes share as ancestors aquatic worms that lived 600 million years ago; and all plants and animals derive from bacteria-like microorganisms that originated more than 3 billion years ago. Biological evolution is a process of descent with modification. Lineages of organisms change through generations; diversity arises because the lineages that descend from common ancestors diverge through time.

The 19th-century English naturalist Charles Darwin argued that organisms come about by evolution, and he provided a scientific explanation , essentially correct but incomplete, of how evolution occurs and why it is that organisms have features—such as wings, eyes, and kidneys—clearly structured to serve specific functions. Natural selection was the fundamental concept in his explanation. Natural selection occurs because individuals having more-useful traits, such as more-acute vision or swifter legs, survive better and produce more progeny than individuals with less-favourable traits. Genetics , a science born in the 20th century, reveals in detail how natural selection works and led to the development of the modern theory of evolution. Beginning in the 1960s, a related scientific discipline , molecular biology , enormously advanced knowledge of biological evolution and made it possible to investigate detailed problems that had seemed completely out of reach only a short time previously—for example, how similar the gene s of humans and chimpanzees might be (they differ in about 1–2 percent of the units that make up the genes).

This article discusses evolution as it applies generally to living things. For a discussion of human evolution, see the article human evolution . For a more complete treatment of a discipline that has proved essential to the study of evolution, see the articles genetics, human and heredity . Specific aspects of evolution are discussed in the articles coloration and mimicry . Applications of evolutionary theory to plant and animal breeding are discussed in the articles plant breeding and animal breeding . An overview of the evolution of life as a major characteristic of Earth’s history is given in community ecology: Evolution of the biosphere . A detailed discussion of the life and thought of Charles Darwin is found in the article Darwin, Charles .

General overview

The evidence for evolution.

Darwin and other 19th-century biologists found compelling evidence for biological evolution in the comparative study of living organisms, in their geographic distribution, and in the fossil remains of extinct organisms. Since Darwin’s time, the evidence from these sources has become considerably stronger and more comprehensive , while biological disciplines that emerged more recently—genetics, biochemistry , physiology , ecology , animal behaviour (ethology), and especially molecular biology—have supplied powerful additional evidence and detailed confirmation. The amount of information about evolutionary history stored in the DNA and proteins of living things is virtually unlimited; scientists can reconstruct any detail of the evolutionary history of life by investing sufficient time and laboratory resources.

Evolutionists no longer are concerned with obtaining evidence to support the fact of evolution but rather are concerned with what sorts of knowledge can be obtained from different sources of evidence. The following sections identify the most productive of these sources and illustrate the types of information they have provided.

• Biology Important Questions
• Class 12 - Biology
• Chapter 7: Evolution

Important Questions for Class 12 Chapter 7: Evolution

Evolution refers to the change in the characteristics of species over several generations based on the process of natural selection. The organisms go through certain genetic changes due to mutation and other significant reasons and evolve over successive generations. The organisms which can adapt to the changing environmental conditions are selected by nature, the rest are eliminated. This process was named as natural selection by Charle’s Darwin.

Very Short Answer Type Questions

Q.1. List the characteristics of fossils.

A.1. The characteristics of fossils are mentioned below:

Fossils provide a connecting link between different species.

They help in identifying the time period when they existed.

They represent modes of preservation of different ancient species.

They helped in identifying the evolutionary traits of the organisms and their ancestors.

Q.2. How is the age of living tree estimated?

A.2. The age of the living tree can be calculated by counting the annual rings on the wood growth.

Q.3. Name the process to estimate the age of a fossil.

A.3. The age of a fossil is determined by carbon dating.

Q.4. What is the pre-condition for adaptive radiation?

A.4. The pre-condition for adaptive radiation is forming physical and geographical barriers between the population of the same species.

Q.5. How is the age of rock estimated?

A.5. The age of the rock is estimated by measuring the amount of certain radioactive elements in the rock. The age of the rock is known as the absolute age.

Q.6. What is the founder effect?

A.6. The founder effect is a type of genetic drift which occurs when a few individuals in a population separate from the original population and form a colony. The genetic diversity of this new population will not be the same as that of the original population. This is a gradual process.

Q.7. What is the bottleneck effect?

A.7. The bottleneck effect is a type of genetic drift that occurs when the size of a population is severely reduced due to events such as earthquakes, epidemics, floods, fire, etc. In this process, a large number of organisms are deceased leaving behind only a handful of the population. Now, the genetic diversity of the surviving population becomes the genetic diversity of the entire population.

Also read: Mechanism of Evolution

Q.8. What is natural selection?

A.8. Natural selection is the process in which the survival and reproductive rate of individuals with certain characteristics are greater than that of the other individuals in a population. This process leads to an evolutionary change.

Q.9. What are the factors affecting the Hardy-Weinberg equilibrium?

A.9. The factors affecting the Hardy-Weinberg equilibrium are:

Genetic Recombination

• Genetic Drift

Natural Selection

Q.10. What are the various stages of evolution?

A.10. There are seven stages in human evolution :

Dryopithecus

Ramapithecus

Australopithecus

Homo Erectus

Homo Sapiens Neanderthalensis

Homo Sapiens Sapiens

Short Answer Type Questions

Q.1. What do you mean by “survival of the fittest”?

A.1. The term “survival of the fittest” was coined by Darwin in support of his theory of natural selection . The organisms that adapt to the changing environmental conditions and overcome the competitions for food and space are selected by nature to survive. In simple terms, the organisms that are physically in good shape and health are considered “fit”. The ones that aren’t are eliminated. This is known as “survival of the fittest”.

Q.2. Comment on the statement, “Migration may increase or decrease the effects of selection”.

A.2. Migration is the movement of individuals from one place to another. The individuals can either move to a different population or move into a particular population. Movement of individuals to a different population might remove certain alleles that confer better adaptations . Movement into a particular population might add certain alleles that blur the effects of selection. Thus we can say that migration can increase or decrease the effects of selection.

Q.3. Explain the terms:

Race – Race may be different phenotypic populations within the same species. It is used as rank higher than the strains but lower than the species. Eg., Mongoloid, Negroid

Breed – Breed is a morphologically and physiologically distinct sub-group of a race where crossing occurs within the sub-group to maintain its individuality. For eg., Rhode island red, Plymouth red.

Cultivars – It is a group of plants selected by plant breeders for desirable characteristics that can be maintained by propagation. Eg., roses, daffodils

Variety – It is a morphologically, physiologically, and genetically distinct sub-group of species. Eg., cauliflower, cabbage

Q.4. How is nascent oxygen toxic to aerobic living organisms?

A.4. Nascent oxygen is very reactive and can react with all types of biomolecules present in living organisms, such as DNA, proteins and enzymes. It can cause mutation in DNA and can degrade proteins and enzymes on reactions, hence, toxic to aerobic life forms.

Q.5. Creation and presence of variation are directionless, but natural selection is directional as it is in the context of adaptation. Comment.

A.5. Variation is considered directionless because it is spontaneous and random. It is seen in sexually reproducing organisms which occurs as a result of crossing over during meiosis or fusion of gametes. The variations which help the individuals in adapting to the environment are passed on to successive generations. Natural selection is directional because it leads only to one path, i.e., selection. It is an evolutionary change that leads to the survival of the fittest and elimination of the unfit individuals.

Q.6. Comment on the statement with reference to industrial melanism, “Evolution is apparently reversible”.

A.6. The peppered moth resided on the surface of the lichens and protected itself from the predators due to camouflage. During industrialization in Europe, the surface of the lichens turned black due to the emissions from the coal-based industries. The moths were now easily visible to the predators and got eliminated gradually. A mutant of peppered moth flourished during this period. It was not visible to the predators due to its black colour and hence was selected by nature. Clean air legislation was passed in Europe in 1956 as a result of which the emission of smoke decreased. The non-melanic peppered moth is appearing again along with the lichens. This proves that evolution is reversible.

Also read: Industrial Melanism

Q.7. What is genetic drift?

A.7. Genetic drift is a mechanism of evolution in which the allele frequencies change over generations as a matter of chance. It occurs in populations of all sizes but its effect is the maximum in a small population. Genetic drift is observed when there is a sudden decline in the population due to natural disasters (bottleneck effect), or when a new population separates from the original population to form a colony (founder effect). Genetic drift does not take into account whether the allele is beneficial or harmful to the individual carrying it. It is possible that a beneficial allele is lost and a harmful allele persists.

Q.8. Explain adaptive radiation. Give examples in support of your answer.

A.8. Adaptive radiation is the process in which a living organism diversifies from a single ancestor into multiple new forms. This is mainly due to changes in the environment. Darwin’s Finches is one fine example of adaptive radiation. The finches of the Galapagos island are seen with a variety of beaks depending upon the type of food they feed on. A single species got adapted to the environmental and nutritional conditions and developed respective beak types over the years.

Q.9. How is convergent evolution different from divergent evolution?

A.9. When two or more species belonging to different ancestors develop similar characteristics due to adaptation to a particular environment, it is known as convergent evolution . On the contrary, when the species belonging to the same ancestors develop different characteristics due to environmental changes and evolve into some new species, it is known as divergent evolution.

Also read: Difference between Homologous and Analogous Structures

Q.10. State the Hardy-Weinberg principle.

A.10. The Hardy-Weinberg principle states that in a large population not affected by the evolutionary processes such as mutation, selection or migration, the allele frequencies and the genotype frequencies are constant from one generation to the other. The principle can be explained by the simple equation: (p+q) 2 = p 2 +q 2 + 2pq = 1 Where, p = frequency of allele A q = frequency of allele a p 2 = frequency of individual AA q 2 = frequency of individual aa 2pq = frequency of individual Aa.

Q.11. How does genetic variation help in evolution?

A.11.  Genetic variation is important in evolution because it allows natural selection to increase or decrease the frequency of alleles already present in the population. These variations enable a few individuals to adapt to the environment.

Long Answer Type Questions

Q.1. Enumerate the key concepts in the evolution theory of Darwin.

A.1. The two key concepts of Darwin’s theory of evolution are:

• Branching Descent

Branching Descent- It is the process in which new species originate from a single ancestor. They became adapted to the new environment through reproductive isolation. For eg., Darwin’s finches which evolved from a single grain eater species.

Natural Selection- In this process, the variations in an individual facilitate better survival of species. They reproduce in large numbers. These variations are passed on to successive generations which help them to survive in the changing environmental conditions. For eg., few giraffes have long necks while others have short necks. If the low-lying shrubs are eliminated for some reason, the giraffes with short necks would be replaced by giraffes with long necks.

Q.2. Describe the phenomenon in which two organisms occupying the same geographical area show the same strategies of adaptation.

A.2. The phenomenon is convergent evolution. In this process, two organisms belonging to different species, descending from different ancestors, evolve similar traits in order to adapt to a similar environment. For eg., the streamlined body of sharks and dolphins. Sharks are fishes while dolphins are mammals but both of them have developed streamlined bodies to adapt themselves to swift swimming. Spines are modified leaves and thorns are modified stems. Both look alike and have a similar function of protecting the plants, but are distantly related to each other.

Q.3. What is the driving force behind divergent evolution? Explain.

A.3. Adaptation is the driving force behind divergent evolution. Divergent evolution is the phenomenon in which the organisms descending from common ancestors evolve gradually into a new species. The new species thus formed adapt themselves to the new habitat and environmental conditions. For eg., the forelimbs of bats, cheetahs, whales and humans have the same anatomical structures but perform different functions. Thus, in these animals, the same structure evolved into different forms according to the needs of the animals.

Q.4. Which law states that the sum of allelic frequencies in a population is constant? List the five factors that influence the law. A.4. The law is Hardy-Weinberg equilibrium . The five factors influencing the law are:

Genetic drift

Q.5. If the industries were removed, what impact would it have on the population of moths in England? A.5. The two variants of peppered moths, black and grey, were already existing in the population. They resided on the surface of the lichens. Before industrialization, the grey moths were not spotted by the predators due to the camouflage. However, the black moths were easily visible and killed by the predators. If the industries were removed, the population of the black variants would have reduced to a large extent leaving behind the grey population of peppered moths.

Q.6. What are the types of evolution

A.6.  The different types of evolution are:

• Convergent evolution– It is the process, which evolves independently, under similar selection pressures. For example, flying insects, birds and other flying species have all evolved the ability to fly, but independently of each other.
• Coevolution evolution– It is the process in which two or more species evolve in tandem by exerting selection pressures on each other. For example, host and parasites, predators and prey,  flowering plants and pollinating insects and mutualistic or symbiotic interactions.
• Adaptive radiation– It is the process in which a species splits into a number of new forms when a change in the environment makes new resources available or creates new environmental challenges. For example, finches on the Galapagos Islands have developed different shaped beaks to take advantage of the different kinds of food available on different islands.

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The Smithsonian Institution's Human Origins Program

• Introduction to Human Evolution

Human evolution

Human evolution is the lengthy process of change by which people originated from apelike ancestors. Scientific evidence shows that the physical and behavioral traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years.

One of the earliest defining human traits, bipedalism -- the ability to walk on two legs -- evolved over 4 million years ago. Other important human characteristics -- such as a large and complex brain, the ability to make and use tools, and the capacity for language -- developed more recently. Many advanced traits -- including complex symbolic expression, art, and elaborate cultural diversity -- emerged mainly during the past 100,000 years.

Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens , has a very close relationship to another group of primate species, the apes. Humans and the great apes (large apes) of Africa -- chimpanzees (including bonobos, or so-called “pygmy chimpanzees”) and gorillas -- share a common ancestor that lived between 8 and 6 million years ago. Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa.

Most scientists currently recognize some 15 to 20 different species of early humans. Scientists do not all agree, however, about how these species are related or which ones simply died out. Many early human species -- certainly the majority of them – left no living descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species.

Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, between 1.5 million and 1 million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years and to the Americas within the past 30,000 years or so. The beginnings of agriculture and the rise of the first civilizations occurred within the past 12,000 years.

Paleoanthropology

Paleoanthropology is the scientific study of human evolution. Paleoanthropology is a subfield of anthropology, the study of human culture, society, and biology. The field involves an understanding of the similarities and differences between humans and other species in their genes, body form, physiology, and behavior. Paleoanthropologists search for the roots of human physical traits and behavior. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people. For many people, paleoanthropology is an exciting scientific field because it investigates the origin, over millions of years, of the universal and defining traits of our species. However, some people find the concept of human evolution troubling because it can seem not to fit with religious and other traditional beliefs about how people, other living things, and the world came to be. Nevertheless, many people have come to reconcile their beliefs with the scientific evidence.

Early human fossils and archeological remains offer the most important clues about this ancient past. These remains include bones, tools and any other evidence (such as footprints, evidence of hearths, or butchery marks on animal bones) left by earlier people. Usually, the remains were buried and preserved naturally. They are then found either on the surface (exposed by rain, rivers, and wind erosion) or by digging in the ground. By studying fossilized bones, scientists learn about the physical appearance of earlier humans and how it changed. Bone size, shape, and markings left by muscles tell us how those predecessors moved around, held tools, and how the size of their brains changed over a long time. Archeological evidence refers to the things earlier people made and the places where scientists find them. By studying this type of evidence, archeologists can understand how early humans made and used tools and lived in their environments.

The process of evolution

The process of evolution involves a series of natural changes that cause species (populations of different organisms) to arise, adapt to the environment, and become extinct. All species or organisms have originated through the process of biological evolution. In animals that reproduce sexually, including humans, the term species refers to a group whose adult members regularly interbreed, resulting in fertile offspring -- that is, offspring themselves capable of reproducing. Scientists classify each species with a unique, two-part scientific name. In this system, modern humans are classified as Homo sapiens .

Evolution occurs when there is change in the genetic material -- the chemical molecule, DNA -- which is inherited from the parents, and especially in the proportions of different genes in a population. Genes represent the segments of DNA that provide the chemical code for producing proteins. Information contained in the DNA can change by a process known as mutation. The way particular genes are expressed – that is, how they influence the body or behavior of an organism -- can also change. Genes affect how the body and behavior of an organism develop during its life, and this is why genetically inherited characteristics can influence the likelihood of an organism’s survival and reproduction.

Evolution does not change any single individual. Instead, it changes the inherited means of growth and development that typify a population (a group of individuals of the same species living in a particular habitat). Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population. As a result, the offspring inherit those genetic characteristics that enhance their chances of survival and ability to give birth, which may work well until the environment changes. Over time, genetic change can alter a species' overall way of life, such as what it eats, how it grows, and where it can live. Human evolution took place as new genetic variations in early ancestor populations favored new abilities to adapt to environmental change and so altered the human way of life.

Dr. Rick Potts provides a video short introduction to some of the evidence for human evolution, in the form of fossils and artifacts.

• Climate Effects on Human Evolution
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• Evolution and the Anthropocene: Science, Religion, and the Human Future
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• "Shaping Humanity: How Science, Art, and Imagination Help Us Understand Our Origins" (book by John Gurche)
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• Bronze Statues
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