How Does Natural Selection Work?

Domed Tortoises have shorter necks - Click to enlarge
Domed Tortoises have shorter necks
(click to enlarge)
©AMNH
Natural selection is the process by which species evolve over time. Individuals inherit traits, or features, from their parents. No two organisms (except identical twins) are exactly alike. This is called individual variation. Inherited variation comes from the mixture of genetic information from parents, and very occasionally from new mutations (copying errors of DNA). There is a limit to the number of individuals that can survive in any particular environment. Those individuals that have traits that allow them to survive better will tend to pass those characteristics to their offspring. For example, saddleback tortoises have longer necks and can reach high food more easily. On islands that lack food close to the ground, animals with this trait have a better chance of surviving and reproducing compared to their short-necked cousins. So over time, the long-necked tortoises are naturally selected compared to the short-necked tortoises in this environment. This is an example of how a population or species can evolve.

SEARCH SITE MAP FAQ COPYRIGHT INFO PRIVACY POLICY ROSE CENTER CONTACT US SIGN UP FOR AMNH ENOTES Darwin Online Educator's Guide Photo of Charles Darwin