Last updated: February 2, 2026
Definitions of evolution from primary sources, peer-reviewed literature, and scientific organizations.
Charles Darwin, On the Origin of Species (1859)
"I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species."
On the Origin of Species, First Edition (Project Gutenberg)
Darwin's term for evolution was "descent with modification"—the idea that species change over time and share common ancestors.1
Theodosius Dobzhansky (1973)
"Nothing in biology makes sense except in the light of evolution... Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light it becomes a pile of sundry facts—some of them interesting or curious but making no meaningful picture as a whole."2
Nature Scitable
"Evolution is a process that results in changes in the genetic material of a population over time."3
National Academy of Sciences
"Evolution consists of changes in the heritable traits of a population of organisms as successive generations replace one another. It is populations of organisms that evolve, not individual organisms."4
See also: 5
American Association for the Advancement of Science (AAAS)
"Evolution is one of the most robust and widely accepted principles of modern science."6
American Institute of Biological Sciences
"The theory of evolution is the only scientifically defensible explanation for the origin of life and development of species. A theory in science, such as the atomic theory in chemistry and the Newtonian and relativity theories in physics, is not a speculative hypothesis, but a coherent body of explanatory statements supported by evidence."7
National Human Genome Research Institute
"Evolution, as related to genomics, refers to the process by which living organisms change over time through changes in the genome. Such evolutionary changes result from mutations that produce genomic variation, giving rise to individuals whose biological functions or physical traits are altered."8
University of California Museum of Paleontology
"Biological evolution, simply put, is descent with inherited modification."9
Encyclopedia Britannica
"Evolution [is a] 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."10
The theory of evolution scientifically explains these interconnected observations about life's diversity and history.
The scientific community is unanimous: the mechanisms that drive small-scale changes (microevolution) are the same mechanisms that, over longer time periods, produce large-scale changes (macroevolution) including the origin of new species and higher taxonomic groups.
The distinction between microevolution and macroevolution is one of time scale and degree of change, not a difference in mechanism. Attempts to accept microevolution while rejecting macroevolution differ from the scientific consensus on evolutionary processes.