short essay about evolution

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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October 19, 2023

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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
• 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
• 'Hobbits' on Flores, Indonesia
• Earliest Humans in China
• Bose, China
• Anthropocene: The Age of Humans
• Fossil Forensics: Interactive
• What's Hot in Human Origins?
• Instructions
• Carnivore Dentition
• Ungulate Dentition
• Primate Behavior
• Footprints from Koobi Fora, Kenya
• Laetoli Footprint Trails
• Footprints from Engare Sero, Tanzania
• 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
• Stone Sickle Blades
• Projectile Point
• Oldest Pottery
• Pottery Fragment
• Fire-Altered Stone Tools
• Terra Amata Shelter
• Qafzeh: Oldest Intentional Burial
• Assyrian Cylinder Seal
• Blombos Ocher Plaque
• Ishango Bone
• Bone and Ivory Needles
• Carved Ivory Running Lion
• Female torso in ivory
• Ivory Horse Figurine
• Ivory Horse Sculpture
• Lady of Brassempouy
• Lion-Man Figurine
• Willendorf Venus
• Ancient Shell Beads
• Carved Bone Disc
• Cro-Magnon Shell Bead Necklace
• Oldest Known Shell Beads
• Ancient Flute
• Ancient Pigments
• Apollo 11 Plaque
• Carved antler baton with horses
• Geometric incised bone rectangle
• Tata Plaque
• 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
• Walking Upright
• Tools & Food
• Social Life
• Language & Symbols
• Humans Change the World
• 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?
• Why do we have wisdom teeth?
• Human Origins Glossary
• Learning Unity and Diversity in Alabama
• Teaching Evolution through Human Examples
• Frequently Asked Questions
• Recommended Books
• Exhibit Floorplan Interactive
• Print Floorplan PDF
• Reconstructions of Early Humans
• Chesterfield County Public Library
• Orange County Library
• Andover Public Library
• Ephrata Public Library
• Oelwein Public Library
• Cedar City Public Library
• Milpitas Library
• Spokane County Library
• Cottage Grove Public Library
• Pueblo City-County Library
• Springfield-Greene County Library
• Peoria Public Library
• Orion Township Public Library
• Skokie Public Library
• Wyckoff Free Public Library
• Tompkins County Public Library
• Otis Library
• Fletcher Free Library
• Bangor Public Library
• Payne Theological Seminary
• Columbia Theological Seminary
• Yuma County Library
• Hood Theological Seminary & Livingstone College
• Broward County Public Library
• Human Origins Do it Yourself Exhibit
• Exhibit Field Trip Guide
• Acknowledgments
• Human Origins Program Team
• Connie Bertka
• Betty Holley
• Nancy Howell
• Lee Meadows
• Jamie L. Jensen
• David Orenstein
• Michael Tenneson
• Leonisa Ardizzone
• Fatimah Jackson
• Shai Cherry
• David Haberman (Emeritus)
• Fred Edwords (Emeritus)
• Elliot Dorff (Emeritus)
• Francisca Cho (Emeritus)
• Peter F. Ryan (Emeritus)
• Mustansir Mir (Emeritus)
• Randy Isaac (Emeritus)
• Mary Evelyn Tucker (Emeritus)
• Wentzel van Huyssteen (Emeritus)
• Joe Watkins (Emeritus)
• Tom Weinandy (Emeritus)
• 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?"
• Volunteer Opportunities
• Submit Question
• "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