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Evolution Explainer

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A guided path through evolution in ten short steps. Read them in order: each one builds on the last. Your progress is saved in this browser only.

  1. What is evolution? Evolution is change in the inherited traits of a population over generations. Mutation, natural selection, genetic drift, and gene flow drive it, and over deep time it links all living things in one family tree.
  2. Natural selection Natural selection happens when individuals with certain inherited traits leave more offspring than others in a particular environment. Scientists have measured it in the wild, in mice, moths, and finches.
  3. Mutation A mutation is a change in DNA. Each person is born with roughly 50 to 70 new ones. Most do nothing, some cause harm, and a few help. They arise at random with respect to need, and they supply the raw variation that evolution works with.
  4. Genetic drift Genetic drift is evolutionary change caused by random sampling. It can make variants more or less common even when they neither help nor hurt, and its effects are strongest in small populations.
  5. Speciation Speciation is when one lineage splits into two that no longer share genes freely. It can follow geographic separation, a switch to a new food plant, or a doubling of chromosomes. It can take one generation or millions of years.
  6. Evidence for evolution Evolution is supported by many lines of evidence, not just one. Fossils, DNA, anatomy, and direct observations point to the same broad picture.
  7. Fossil evidence Fossils do not give a perfect movie of the past, but they do show a strong pattern of change through time that matches evolution.
  8. Genetic evidence DNA is one of the strongest lines of evidence for evolution because it lets scientists compare inherited information directly across living things.
  9. Observed evolution Evolution is not only inferred from the distant past. Scientists can observe populations changing today in labs, hospitals, farms, and natural environments.
  10. Common misconceptions Many misunderstandings about evolution come from everyday meanings of words like theory, random, and ancestor. This section slows down those words and explains them correctly.