essay evolution of human beings

Human Evolution

Six million years of human evolution.

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

Paleoanthropology is the scientific study of human evolution which investigates the origin of the universal and defining traits of our species. 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 biological traits and behavior. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people.

What Can Human Fossils Tell Us?

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.

Humans and Our Evolutionary Relatives

Humans are primates . Physical and genetic similarities show that the modern human species, Homo sapiens, are most closely related to a group of primate species, the apes. Modern humans and other 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. Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, by 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 20,000 years or so.

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.

Human Characteristics

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. The beginnings of agriculture and the rise of the first civilizations occurred at least within the past 12,000 years.

Smithsonian Research Into Human Evolution

The Smithsonian’s Human Origins Program explores the universal human story at its broadest time scale. Smithsonian anthropologists research many aspects of human evolution around the globe, investigating fundamental questions about our evolutionary past, including the roots of human adaptability.

For example, paleoanthropologist Dr. Rick Potts – who directs the Human Origins Program – co-directs ongoing research projects in southern and western Kenya and southern and northern China that compare evidence of early human behavior and environments from eastern Africa to eastern Asia. Rick’s work helps us understand the environmental changes that occurred during the times that many of the fundamental characteristics that make us human – such as making tools and large brains – evolved, and that our ancestors were often able to persist through dramatic climate changes. Rick describes his work in the video Survivors of a Changing Environment .

Dr. Briana Pobiner is a paleoanthropologist whose research centers on the evolution of human diet (with a focus on meat-eating), but has included topics as diverse as cannibalism and chimpanzee carnivory. Her research has helped us understand that at the onset of human carnivory over 2.5 million years ago some of the meat our ancestors ate was scavenged from large carnivores, but by 1.5 million years ago they were getting access to some of the prime, juicy parts of large animal carcasses. She uses techniques similar to modern day forensics for her detective work on early human diets.

Geologist Dr. Kay Behrensmeyer has been a long-time collaborator with Rick Potts’s human evolution research at the site of Olorgesailie in southern Kenya. Kay’s role with the research there is to help understand the environments of the sites at which evidence for early humans – in the form of stone tools as well as fossils of the early humans themselves – have been found, by looking at the sediments of the geological layers in which the artifacts and fossils have been excavated.

This article was updated October 18, 2024.

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The Smithsonian Institution's Human Origins Program

Human characteristics: what does it mean to be human.

Part of what it means to be human is how we became human. Over a long period of time, as early humans adapted to a changing world, they evolved certain characteristics that help define our species today.

This section of our website focuses on several human characteristics that evolved over the past 6 million years. As you explore the scientific evidence for these characteristics, you will discover that these traits did not emerge all at once or in any one species. There were important milestones along the way. For example, early humans began walking upright before they began making tools. A rapid increase in brain size occurred before early humans began using symbols to communicate. And all of these traits emerged before humans began domesticating plants and animals.

• Walking Upright

The earliest humans climbed trees and walked on the ground. This flexibility helped them get around in diverse habitats and cope with changing climates.

• Tools & Food

Early humans butchered large animals at least 2.6 million years ago. By at least 500,000 years ago, early humans made wooden spears and used them to kill large animals.

As early humans spread to different environments, they evolved body shapes that helped them survive in hot and cold climates. Changing diets also led to changes in body shape.

As early humans faced new environmental challenges and evolved bigger bodies, they evolved larger and more complex brains.

• Social Life

Sharing food, caring for infants, and building social networks helped our ancestors meet the daily challenges of their environments.

• Language & Symbols

From pigments to printing presses, symbols changed the way humans lived and provided new ways to cope with an unpredictable world.

• Humans Change the World

Within just the past 12,000 years, our species, Homo sapiens , made the transition to producing food and changing our surroundings. We have been so successful that we have inadvertently created a turning point in the history of life on Earth.

• Climate Effects on Human Evolution
• Survival of the Adaptable
• Human Evolution Timeline Interactive
• 2011 Olorgesailie Dispatches
• 2004 Olorgesailie Dispatches
• 1999 Olorgesailie Dispatches
• Olorgesailie Drilling Project
• Kanam, Kenya
• Kanjera, Kenya
• Ol Pejeta, Kenya
• Olorgesailie, Kenya
• Evolution of Human Innovation
• Adventures in the Rift Valley: Interactive
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• Earliest Humans in China
• Bose, China
• Anthropocene: The Age of Humans
• Fossil Forensics: Interactive
• What's Hot in Human Origins?
• Instructions
• Carnivore Dentition
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• Primate Behavior
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• Hammerstone from Majuangou, China
• Handaxe and Tektites from Bose, China
• Handaxe from Europe
• Handaxe from India
• Oldowan Tools from Lokalalei, Kenya
• Olduvai Chopper
• Stone Tools from Majuangou, China
• Middle Stone Age Tools
• Burin from Laugerie Haute & Basse, Dordogne, France
• La Madeleine, Dordogne, France
• Butchered Animal Bones from Gona, Ethiopia
• Katanda Bone Harpoon Point
• Oldest Wooden Spear
• Punctured Horse Shoulder Blade
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• Mystery Skull Interactive
• Shanidar 3 - Neanderthal Skeleton
• One Species, Living Worldwide
• Human Skin Color Variation
• Ancient DNA and Neanderthals
• Human Family Tree
• Swartkrans, South Africa
• Shanidar, Iraq
• Introduction to Human Evolution
• Nuts and bolts classification: Arbitrary or not? (Grades 6-8)
• The Origins and Evolution of Human Bipedality (Grades 9-12)
• Comparison of Human and Chimp Chromosomes (Grades 9-12)
• Hominid Cranial Comparison: The "Skulls" Lab (Grades 9-12)
• Investigating Common Descent: Formulating Explanations and Models (Grades 9-12)
• Fossil and Migration Patterns in Early Hominids (Grades 9-12)
• For College Students
• Why do we get goose bumps?
• Chickens, chimpanzees, and you - what do they have in common?
• Grandparents are unique to humans
• How strong are we?
• Humans are handy!
• Humans: the running ape
• Our big hungry brain!
• Our eyes say it!
• The early human tool kit
• The short-haired human!
• The “Nutcracker”
• What can lice tell us about human evolution?
• What does gut got to do with it?
• Why do paleoanthropologists love Lucy?
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• Human Origins Do it Yourself Exhibit
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• Members Thoughts on Science, Religion & Human Origins (video)
• Science, Religion, Evolution and Creationism: Primer
• The Evolution of Religious Belief: Seeking Deep Evolutionary Roots
• Laboring for Science, Laboring for Souls:  Obstacles and Approaches to Teaching and Learning Evolution in the Southeastern United States
• Public Event : Religious Audiences and the Topic of Evolution: Lessons from the Classroom (video)
• Evolution and the Anthropocene: Science, Religion, and the Human Future
• Imagining the Human Future: Ethics for the Anthropocene
• Human Evolution and Religion: Questions and Conversations from the Hall of Human Origins
• I Came from Where? Approaching the Science of Human Origins from Religious Perspectives
• Religious Perspectives on the Science of Human Origins
• Submit Your Response to "What Does It Mean To Be Human?"
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• "Shaping Humanity: How Science, Art, and Imagination Help Us Understand Our Origins" (book by John Gurche)
• What Does It Mean To Be Human? (book by Richard Potts and Chris Sloan)
• Bronze Statues
• Reconstructed Faces

Ch. 1 The Study of History and the Rise of Civilization

The evolution of humans, learning objective.

• To understand the process and timeline of human evolution
• Humans began to evolve about seven million years ago, and progressed through four stages of evolution. Research shows that the first modern humans appeared 200,000 years ago.
• Neanderthals were a separate species from humans. Although they had larger brain capacity and interbred with humans, they eventually died out.
• A number of theories examine the relationship between environmental conditions and human evolution.
• The main human adaptations have included bipedalism, larger brain size, and reduced sexual dimorphism.

aridity hypothesis

The theory that the savannah was expanding due to increasingly arid conditions, which then drove hominin adaptation.

turnover pulse hypothesis

The theory that extinctions due to environmental conditions hurt specialist species more than generalist ones, leading to greater evolution among specialists.

Red Queen hypothesis

The theory that species must constantly evolve in order to compete with co-evolving animals around them.

encephalization

An evolutionary increase in the complexity and/or size of the brain.

sexual dimorphism

Differences in size or appearance between the sexes of an animal species.

social brain hypothesis

The theory that improving cognitive capabilities would allow hominins to influence local groups and control resources.

Toba catastrophe theory

The theory that there was a near-extinction event for early humans about 70,000 years ago.

savannah hypothesis

The theory that hominins were forced out of the trees they lived in and onto the expanding savannah; as they did so, they began walking upright on two feet.

A primate of the family Hominidae that includes humans and their fossil ancestors.

Describing an animal that uses only two legs for walking.

Human evolution began with primates. Primate development diverged from other mammals about 85 million years ago. Various divergences among apes, gibbons, orangutans occurred during this period, with Homini (including early humans and chimpanzees) separating from Gorillini (gorillas) about 8 millions years ago. Humans and chimps then separated about 7.5 million years ago.

Skeletal structure of humans and other primates. A comparison of the skeletal structures of gibbons, humans, chimpanzees, gorillas and orangutans.

Generally, it is believed that hominids first evolved in Africa and then migrated to other areas. There were four main stages of human evolution. The first, between four and seven million years ago, consisted of the proto hominins Sahelanthropus , Orrorin  and Ardipithecus. These humans may have been bipedal, meaning they walked upright on two legs. The second stage, around four million years ago, was marked by the appearance of Australopithecus, and the third, around 2.7 million years ago, featured Paranthropus. 

The fourth stage features the genus Homo, which existed between 1.8 and 2.5 million years ago. Homo habilis , which used stone tools and had a brain about the size of a chimpanzee, was an early hominin in this period. Coordinating fine hand movements needed for tool use may have led to increasing brain capacity. This was followed by Homo erectus and Homo ergaster , who had double the brain size and may have been the first to control fire and use more complex tools. Homo heidelbergensis appeared about 800,000 years ago, and modern humans, Homo sapiens , about 200,000 years ago. Humans acquired symbolic culture and language about 50,000 years ago.

Comparison of skull features among early humans.A comparison of Homo habilis, Homo erectus, Homo floresiensis and Homo naledi skull features.

Neanderthals

A separate species, Homo neanderthalensi s, had a common ancestor with humans about 660,000 years ago, and engaged in interbreeding with Homo sapiens about 45,000 to 80,000 years ago. Although their brains were larger, Neanderthals had fewer social and technological innovations than humans, and they eventually died out.

Theories of Early Human Evolution

The savannah hypothesis states that hominins were forced out of the trees they lived in and onto the expanding savannah; as they did so, they began walking upright on two feet. This idea was expanded in the aridity hypothesis, which posited that the savannah was expanding due to increasingly arid conditions resulting in hominin adaptation. Thus, during periods of intense aridification, hominins also were pushed to evolve and adapt.

The turnover pulse hypothesis states that extinctions due to environmental conditions hurt specialist species more than generalist ones. While generalist species spread out when environmental conditions change, specialist species become more specialized and have a greater rate of evolution. The Red Queen hypothesis states that species must constantly evolve in order to compete with co-evolving animals around them. The social brain hypothesis states that improving cognitive capabilities would allow hominins to influence local groups and control resources. The Toba catastrophe theory states that there was a near-extinction event for early humans about 70,000 years ago.

Human Adaptations

Bipedalism, or walking upright, is one of the main human evolutionary adaptations. Advantages to be found in bipedalism include the freedom of the hands for labor and less physically taxing movement. Walking upright better allows for long distance travel and hunting, for a wider field of vision, a reduction of the amount of skin exposed to the sun, and overall thrives in a savannah environment. Bipedalism resulted in skeletal changes to the legs, knee and ankle joints, spinal vertebrae, toes, and arms. Most significantly, the pelvis became shorter and rounded, with a smaller birth canal, making birth more difficult for humans than other primates. In turn, this resulted in shorter gestation (as babies need to be born before their heads become too large), and more helpless infants who are not fully developed before birth.

Larger brain size, also called encephalization, began in early humans with Homo habilis and continued through the Neanderthal line (capacity of 1,200 – 1,900 cm3). The ability of the human brain to continue to grow after birth meant that social learning and language were possible. It is possible that a focus on eating meat, and cooking, allowed for brain growth. Modern humans have a brain volume of 1250 cm3.

Humans have reduced sexual dimorphism, or differences between males and females, and hidden estrus, which means the female is fertile year-round and shows no special sign of fertility. Human sexes still have some differences between them, with males being slightly larger and having more body hair and less body fat. These changes may be related to pair bonding for long-term raising of offspring.

Other adaptations include lessening of body hair, a chin, a descended larynx, and an emphasis on vision instead of smell.

Human Evolution

A video showing evolution from early animals to modern humans.

Candela Citations

• Boundless World History. Authored by : Boundless. Located at : https://courses.lumenlearning.com/boundless-worldhistory/ . License : CC BY: Attribution

Human Evolution: Timeline, Stages, Theories & Evidence

The theory of evolution forms the basis of virtually every other idea in contemporary biology, from the startlingly close similarities between dinosaurs and birds to mechanism of antibiotic resistance. Charles Darwin's name is essentially synonymous with the concept, but it was in fact the combined brainchild of Darwin and the much less heralded Alfred Russell Wallace, who independently arrived at the notion of natural selection.

Wallace and Darwin wound up collaborating on an 1858 publication that preceded Darwin's magnum opus, On the Origin of Species .

The idea of evolution was controversial in its day and remains so today, mainly because it encompasses humans as well as all of the other forms of life on Earth, in some ways dispensing of the notion that humans enjoy an exalted place in the pantheon of living things.

Nevertheless, the evidence for human evolution, and the fact that humans evolved from a primate common ancestor, is as scientifically unassailable as anything else in biology, physics, chemistry or any other field of scientific inquiry.

Above all, learning the facts about human origins is fascinating beyond measure.

Evolution Defined

Evolution, in the world of biology, refers to "descent with modification," a process that is reliant on natural selection . Natural selection in turn refers to the ability of organisms that possess favorable traits within their own environment to survive better than other animals in the same environment. This includes other animals in the same species that do not possess these traits. Evolution can be defined as a change in the frequency of genes in a population over time.

A typical example is a group of giraffes that eat from the leafy branches of trees.

Those that happen to possess longer necks will be able to feed themselves more readily, leading to a higher survival rate among these giraffes. Because giraffe neck length is a heritable trait, meaning that it can be passed to the next generation through genes encoded in deoxyribonucleic acid (DNA, the "genetic material" in all living things on the planet), longer-necked giraffes become more prevalent in this group, and those with shorter necks accordingly die off.

Importantly, natural selection is not a process of conscious striving; it is a matter of luck, with nature choosing the organisms that are the "fittest" in reproductive terms. In addition, an animal that may be "strong" in one setting may find conditions in another immediately lethal. Humans and virtually all other organisms, for example, would be unable to survive in the deep-water thermal vents in which certain bacteria-like organisms can live.

Evidence for Theories of Human Evolution

All organisms are descended from a common ancestor, and humans, being primates, share a common ancestor with other primates that lived relatively recently in the grand scheme of life. The first living things appeared on earth some 3.5 billion years ago, "only" a billion or so years after the Earth itself formed. Modern humans share a common ancestor with other apes of today that lived about 6 million to 8 million years ago.

Most of the evidence for evolution of human beings comes from fossil evidence, and this evidence has been strongly reinforced by the methods of modern molecular biology, such as DNA analysis. The structure of DNA was not confirmed until the 1950s, about 100 years after Darwin and Wallace first arrived at the mechanism by which evolution occurs at the cellular level.

Paleoanthropology is the scientific study of human evolution that combines paleontology (the examination and analysis of the fossil record) with the study of human cultures and societies through the lens of biology ( anthropology ). Paleoanthropologists, then, are scientists who analyze early species of hominids , or early humans.

Some 15 to 20 known hominid species arose over a considerable period of time before modern humans evolved into the 7 billion or so people that populate the planet as of the close of the 21st century's second decade. All but one of these, despite their considerable ingenuity and resourcefulness in comparison to their forebears and non-hominid contemporaries, went extinct.

Common Features of Humans and Apes

Importantly, apes are not distinct from humans; instead, humans are a kind of ape, just as humans are a type of primate, mammal and so on up the taxonomic classification chain.

But for explanatory purposes here, humans and apes will be treated as distinct life forms. Other apes include chimpanzees, bonobos ("pygmy chimps"), gorillas, orangutans and gibbons.

The first four of these are known as the "great apes" because of their larger size.

As hominids evolved over time, the world witnessed the emergence of primates that combine apelike and human features, with the gradual loss of more apelike features for humanlike features.

Common features of apes are a strong brow, an elongated skull, incomplete bipedalism (i.e., "knuckle-walking"), smaller brains, larger canine teeth and a sloping face. Common human features, in contrast, are a shorter face, a non-elongated skull, larger brains, a more complex cultural and community system, small canine teeth, a spinal cord positioned more directly underneath the skull (a trait indicative of bipedalism) and the use of stone tools.

Human Evolution: Timeline and Stages

The first primates appeared some 55 million years ago, about 10 million years after the last dinosaurs walked the Earth. The first orangutans split from what became the human branch of the primate family tree perhaps 10 million years ago; gorillas arrived on the scene about 8 million years ago and split from humans' common ancestor.

Among the apes, the closest relatives of humans are bonobos and chimpanzees, as established by both the fossil record and DNA evidence. The common ancestor of humans, chimpanzees and bonobos that evolved into being 6 million to 8 million years ago gave rise to a succession of ancestors of hominids (and hence of modern humans, or Homo sapiens ) known as hominins .

The oldest apelike relative of humans originated in central Africa and dispersed around the globe from there.

• The 13-million-year-old skull of an infant primate, believed to be a common ancestor of all apes and humans, was found in Kenya in 2014.

Bipedalism , which is the ability to walk upright and one of the defining characteristics of hominids, first arose about 6 million years ago, but only became consistent and then obligatory some 4 million years ago.

Hominids first began forming their own tools about 2.6 million years ago, made purposeful use of fire starting about 800,000 years ago and experienced an accelerated increase in brain size between roughly 800,000 and 200,000 years ago.

Most modern human characteristics have evolved in the last 200,000 years, with a shift to farming and agricultural methods from hunting and gathering beginning about 12,000 years ago. This allowed humans to settle in one place and build elaborate social communities and well as reproduce and survive at a faster rate.

Fossil Evidence of Evolution Theories

Fossils have provided paleoanthropologists with a wealth of knowledge about the hominin species and hominid predecessors of modern humans. Some have been placed in the genus Homo , while others belong to now-extinct genera. From oldest to most recent, some of the humanlike species that have graced Earth include:

** Sahelenthropus tchadensis. ** All that exists now of this ancient creature that lived 6 to 7 million years ago are skull parts found in 2001 in west-central Africa. S. tchadensis had a chimp-sized brain, was able to walk on two legs (but was not completely bipedal), had a spinal opening underneath its cranium, featured smaller canine teeth and boasted a prominent brow ridge. It was thus very apelike.

Orrorin tugenensis. A skeleton of this hominin from 6.2 to 5.8 million years ago was also found in 2001, this one in eastern Africa. It had teeth and hands, was able to walk upright but was also arboreal (i.e., it climbed trees), had small human-like teeth and was size of a modern chimpanzee.

Ardipithecus kadabba. This human ancestor lived from 5.8 to 5.2 million years ago, with its remains (a jaw, teeth, hand and foot bones, and arm and clavicle bones) found in 1997 in eastern Africa. These remains establish that the new species was bipedal, and it lived in woodlands and grasslands, mostly the former (an apelike trait).

Ardipithecus ramidus . This creature lived about 4.4 million years ago, with some remains found in 1994 and a partial skeleton, named "Ardi," found in 2009. It walked upright but had opposable toes to climb trees, and lived in the woods.

Australopithecus afarensis. Known colloquially as "Lucy," A. afarensis was an eastern African dweller between 3.85 and 2.95 million years ago, making Lucy the longest-living pre-human species.

Over 300 individual A. afarensis pre-human fossils have been found, and they show that this hominin had rapid child growth and reached maturity faster than modern humans. Lucy had an apelike face, a larger brain than a chimp's but smaller than a modern human's, and small canines.

It was bipedal but could still climb trees; that it could live both in trees and on the ground allowed it to survive many extended climate changes. Lucy is thought to be among first early humans to live on the savannah, or grassy plain.

Australopithecus africanus. This hominin lived from 3.3 to 2.1 million years ago in southern Africa and was discovered in 1924. It had small, humanlike teeth, a larger brain and a rounder brain case (like humans have). However, this bipedal creature also had apelike features (e.g., long arms, a strong jutting jaw beneath a sloping face and shoulders and hands adapted for climbing).

Homo habilis. One of the earliest known ancestors in our own genus ( Homo ) and thus a hominid, "handy man" (the translation of the name from Latin) existed from 2.4 million to 1.4 million years ago in Eastern and Southern Africa. H. habilis is thought to be one of the first species to create stone tools; it had apelike features like long arms and an apelike face, but it also possessed a large brain case and small teeth, and it is known to have used tools.

** Homo erectus ** . This species spread all over Africa and (out of Africa) into Asia 1.89 million to 143,000 years ago. The oldest species are often referred to as Homo ergaster. It had humanlike body proportions, ate a significant amount of meat as well as plants, lived almost solely on the ground and developed a progressively larger brain and brain case.

Fossil evidence showed that this early human cared for its young, old and sick, and was the longest-lived of all of the early hominid species. Its ability to walk and run long distances allowed it to spread far and wide.

** Homo heidelbergensis ** . The first hominids in Europe, these hominids also lived in China and east Africa some 700,000 to 200,000 years ago; it was was the first species to live in colder climates, with short, wide bodies to retain heat.

These european hominids used tools and fire, built "homes" out of wood and rocks, was first species to hunt large animals, and was the direct ancestors of Neanderthals. H. heidelbergensis had a brain size comparable to that of modern humans.

Homo neanderthalensis. This is the famed Neanderthal and lived from about 400,000 to 40,000 years ago throughout Europe and parts of Asia. The closest extinct relative to Homo sapiens , it was shorter, more muscular and stockier than modern humans, and large noses to help with cold air. Neanderthals had a humanlike face, brains as large (or larger) than H. sapiens and lived in shelters such as caves.

It used tools and weapons, made and wore clothes, made "art" and buried its dead; evidence exists that the Neanderthals had primitive language and used symbols, establishing the earliest traces of what is now called culture.

Homo sapiens. Modern humans evolved in Africa spread worldwide 200,000 years ago, and have continued to evolve larger brains and lighter bodies over their evolutionary history. Human faces have also changed over time to have less pronounced jaws and brow lines, smaller teeth and smaller jaws. You are a member of this species.

• Scientists Have Just Uncovered a New, Mysterious Nerve Cell in the Human Brain • Factors Which Have Limited the Growth of the Human Population • Common Spiders in South Africa • Endangered Plants of the Philippines

• Smithsonian National Museum of Natural History Education: Introduction to Human Evolution
• UC Berkeley: Understanding Evolution: The Emergence of Humans
• The Nature Education Knowledge Project: Overview of Hominin Evolution
• Smithsonian National Museum of Natural History: Human Evolution Evidence
• Scientific American: Fossil Reveals What Last Common Ancestor of Humans and Apes Looked Like
• Harvard University Press: Wallace, Darwin, and the Origin of Species

Cite This Article

Beck, Kevin. "Human Evolution: Timeline, Stages, Theories & Evidence" sciencing.com , https://www.sciencing.com/human-evolution-timeline-stages-theories-evidence-13719186/. 21 August 2019.

Beck, Kevin. (2019, August 21). Human Evolution: Timeline, Stages, Theories & Evidence. sciencing.com . Retrieved from https://www.sciencing.com/human-evolution-timeline-stages-theories-evidence-13719186/

Beck, Kevin. Human Evolution: Timeline, Stages, Theories & Evidence last modified August 30, 2022. https://www.sciencing.com/human-evolution-timeline-stages-theories-evidence-13719186/

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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.