Change over time
Evolution is the gradual change in the characteristics of populations of organisms over many generations. Present species have descended from earlier species through a process of change. All living things are related, and the evolutionary tree shows how groups branch from common ancestors.
Evidence for evolution
| Evidence | What it shows |
|---|---|
| Fossils | Remains of past organisms show change in the order of rock layers |
| Comparative anatomy | Similar bones in the limbs of humans, bats and whales (homologous structures) point to a common ancestor |
| Embryology | Embryos of vertebrates look very alike |
| Molecular biology | Closer species have more similar DNA and proteins |
| Geographical distribution | Related species are found in related regions |
Natural selection
Charles Darwin explained how evolution happens by natural selection. Organisms vary. More offspring are produced than can survive. Those with useful variations are better able to survive and breed, and they pass the useful features on. Over many generations these features become common.
Try itSelection in moths
Start with a share of dark moths. Choose how much better the dark moths survive and how many generations pass.
Key terms
- Evolution
- Gradual change of species over generations.
- Natural selection
- Survival and breeding of the best-suited individuals.
- Fossil
- The preserved remains of a past organism.
- Homologous structure
- A structure with the same origin but sometimes a different use.
Summary
- Evolution is gradual change in populations over time.
- Evidence comes from fossils, anatomy, embryos and DNA.
- Natural selection: variation, competition, survival of the fittest, inheritance.
- Useful alleles become more common in a population.