Introduction to evolution

Part of a series on
Evolutionary biology
Darwin's finches by John Gould
Index Introduction Main Outline Glossary Evidence History
Processes and outcomes Population genetics Variation Diversity Mutation Natural selection Adaptation Polymorphism Genetic drift Gene flow Speciation Adaptive radiation Co-operation Coevolution Coextinction Divergence Convergence Parallel evolution Extinction
Natural history Origin of life Common descent History of life Timeline of evolution Human evolution Phylogeny Biodiversity Biogeography Classification Evolutionary taxonomy Cladistics Transitional fossil Extinction event
History of evolutionary theory Overview Renaissance Before Darwin Darwin Origin of Species Before synthesis Modern synthesis Molecular evolution Evo-devo Current research History of speciation History of paleontology (timeline)
Fields and applications Applications of evolution Biosocial criminology Ecological genetics Evolutionary aesthetics Evolutionary anthropology Evolutionary computation Evolutionary ecology Evolutionary economics Evolutionary epistemology Evolutionary ethics Evolutionary game theory Evolutionary linguistics Evolutionary medicine Evolutionary neuroscience Evolutionary physiology Evolutionary psychology Experimental evolution Phylogenetics Paleontology Selective breeding Speciation experiments Sociobiology Island biogeography Systematics Universal Darwinism
Social implications Evolution as fact and theory Social effects Creation–evolution controversy Theistic evolution Objections to evolution Level of support
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In biology, evolution is the process of change in all forms of life over generations, and evolutionary biology is the study of how evolution occurs. Biological populations evolve through genetic changes that correspond to changes in the organisms' observable traits. Genetic changes include mutations, which are caused by damage or replication errors in organisms' DNA. As the genetic variation of a population drifts randomly over generations, natural selection gradually leads traits to become more or less common based on the relative reproductive success of organisms with those traits.

The age of the Earth is about 4.5 billion years.^[1][2][3] The earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.^[4][5][6] Evolution does not attempt to explain the origin of life (covered instead by abiogenesis), but it does explain how early lifeforms evolved into the complex ecosystem that we see today.^[7] Based on the similarities between all present-day organisms, all life on Earth is assumed to have originated through common descent from a last universal ancestor from which all known species have diverged through the process of evolution.^[8]

All individuals have hereditary material in the form of genes received from their parents, which they pass on to any offspring. Among offspring there are variations of genes due to the introduction of new genes via random changes called mutations or via reshuffling of existing genes during sexual reproduction.^[9][10] The offspring differs from the parent in minor random ways. If those differences are helpful, the offspring is more likely to survive and reproduce. This means that more offspring in the next generation will have that helpful difference and individuals will not have equal chances of reproductive success. In this way, traits that result in organisms being better adapted to their living conditions become more common in descendant populations.^[9][10] These differences accumulate resulting in changes within the population. This process is responsible for the many diverse life forms in the world.

The modern understanding of evolution began with the 1859 publication of Charles Darwin's On the Origin of Species. In addition, Gregor Mendel's work with plants helped to explain the hereditary patterns of genetics.^[11] Fossil discoveries in palaeontology, advances in population genetics and a global network of scientific research have provided further details into the mechanisms of evolution. Scientists now have a good understanding of the origin of new species (speciation) and have observed the speciation process in the laboratory and in the wild. Evolution is the principal scientific theory that biologists use to understand life and is used in many disciplines, including medicine, psychology, conservation biology, anthropology, forensics, agriculture and other social-cultural applications.