What is evolution?
Quick answer
Evolution is the process by which populations of living things change over many generations. Its main driving force is natural selection: individuals with traits that help them survive and reproduce pass those traits on more often. Charles Darwin and Alfred Russel Wallace proposed the idea in 1858.
Natural selection in four steps
Natural selection needs only a few simple conditions, which are found in every living population.
- Variation: Individuals in a population differ, partly because of differences in their genes.
- Inheritance: Many of those differences are passed from parents to offspring; see Mendel’s laws of inheritance.
- Competition: More offspring are born than can survive.
- Selection: Individuals with helpful traits tend to survive and reproduce more, so those traits become more common over time.
Over very long periods, these changes can create new species.
Other causes of evolution
| Process | What it does |
|---|---|
| Mutation | Creates new genetic variation; see what DNA is |
| Genetic drift | Random changes, especially strong in small populations |
| Gene flow | Genes move between populations through migration |
| Sexual selection | Traits that help attract mates, like a peacock’s tail |
Evolution you can see
| Example | What happened |
|---|---|
| Peppered moths | During England’s Industrial Revolution, dark moths became common on soot-covered trees |
| Galápagos finches | Beak sizes change measurably after droughts |
| Antibiotic resistance | Bacteria evolve to survive drugs, sometimes in just years |
| Insecticide resistance | Mosquitoes and pests adapt to chemicals |
Common misunderstandings
- “Humans evolved from chimpanzees.” Not quite: humans and chimps share a common ancestor that lived roughly 6–7 million years ago.
- “Evolution is just a theory.” In science, a theory is a well-tested explanation supported by large amounts of evidence, from fossils and DNA to direct observation.
- “Evolution has a goal.” It doesn’t plan ahead; it responds to current conditions.
Darwin’s voyage
Darwin’s ideas grew from observations made on a five-year voyage around the world; see what ship Darwin sailed on. Evidence for evolution also comes from life’s shared chemistry, such as the mitochondria found in nearly all complex cells.
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