Knowledge Atlas

Life · Depth 2 · Introductory · 3 min read

Evolution

How populations of living things change over generations, how natural selection works, and the evidence, from fossils to DNA, that links all life.

Evidence Level 1 · EstablishedOpen on the map
On this page
  1. What is evolution?
  2. Darwin and Wallace
  3. How natural selection works
  4. Other forces that change populations
  5. The evidence
  6. Common misconceptions
  7. Real-life examples
  8. Evidence & sources

What is evolution?

Evolution is the change in a population’s genetic composition over time.[1] It happens to populations, not to individual organisms: you don’t evolve during your lifetime, but your species can change over many generations.[1] Biologists measure that change as shifts in how common particular versions of genes (alleles) are in a population.[2]

Darwin and Wallace

Two naturalists, Charles Darwin and Alfred Russel Wallace, independently worked out the mechanism of evolution.[1] Darwin had travelled around the world on HMS Beagle from 1831 to 1836, visiting the Galápagos Islands.[1] In 1858 both men presented papers on natural selection at the Linnean Society in London, and Darwin’s book On the Origin of Species was published the following year.[1]

How natural selection works

Natural selection rests on three observations:[1]

  1. Most characteristics of organisms are inherited.
  2. More offspring are produced than can survive.
  3. Offspring vary in their characteristics.

Put these together and individuals whose inherited traits help them survive and reproduce leave more offspring, so those traits become more common.[2]

Other forces that change populations

A population’s gene frequencies stay stable unless something acts on them.[2] Besides natural selection, those forces include:

  • Genetic drift: random changes in allele frequencies, with no advantage to the population.[2]
  • The founder effect: an unusual change that starts when an isolated part of a population breaks away.[2]
  • Mutation and migration: a population’s gene frequencies only stay stable if there are no mutations and no migration in or out.[2]

The evidence

  • Fossils show that organisms from the past are not the same as those living today.[1]
  • Anatomy: the bones in human, dog, bird and whale limbs share the same overall construction, a sign of common ancestry.[1]
  • Vestigial structures, like the wings of flightless birds or the hind leg bones of whales, have lost their original function.[1]
  • Embryos: all vertebrate embryos, including humans, have gill slits and tails at some point early in development.[1]
  • Geography: groups that evolved after the supercontinent Pangaea broke up are found only in particular regions.[1]
  • DNA: how closely related two groups are is reflected in how similar their DNA sequences are.[1]

Common misconceptions

  • “It’s just a theory.” In science, a theory is a body of thoroughly tested and verified explanations, not a guess.[1]
  • “Individuals evolve.” Evolution is a change in populations over time.[1]
  • “Evolution explains the origin of life.” The theory doesn’t try to explain how life began.[1]
  • “Organisms evolve on purpose.” Evolution is not goal-directed.[1]

Real-life examples

  • Darwin's finches

    On the Galápagos Islands, Darwin saw finches with differently shaped beaks, and realised each beak helped its bird get a particular kind of food.[1]

  • Why you need a new flu shot

    Flu viruses mutate and multiply quickly, so last year's vaccine may not protect against this year's strain: evolution happening in real time.[2]

  • Whales with leg bones

    Some whales still have hind leg bones, and flightless birds still have wings: 'vestigial' structures left over from their ancestors.[1]

  • Wings, invented twice

    Bats and insects both fly, but they didn't inherit wings from a shared winged ancestor. Similar traits evolved independently: convergent evolution.[1]

Learn more

Short descriptions are our own summaries. The resources belong to, and are run by, their publishers.

  • TextbookFreeIntermediate
    Biology 2e (free textbook) ↗

    by OpenStax

    A free, peer-reviewed university biology textbook, from cells and genetics to evolution and ecology.

Evidence & sources

Level 1 · Established

Supported by extensive evidence and broad scientific consensus.

Why this level? Evolution by natural selection is supported by many independent lines of evidence, from fossils to DNA, as the peer-reviewed biology textbook cited here explains.

This is a Knowledge Atlas editorial classification of the sources we could find, not a certificate of truth. How we evaluate knowledge

Sources

Based on 2 sources from 1 institution: OpenStax.

Show all 2 sourcesHide the list
  1. ScholarlyOpenStax (Rice University)· Academic publisherBiology 2e, 18.1 Understanding EvolutionOpened and checked against this page on 28 Sept 2026 · License: CC BY-NC-SA 4.0
  2. ScholarlyOpenStax (Rice University)· Academic publisherBiology 2e, 19.1 Population EvolutionOpened and checked against this page on 28 Sept 2026 · License: CC BY-NC-SA 4.0