Evolution by Natural Selection

Evolution is the change in the heritable characteristics of a population over successive generations. The central mechanism explaining how populations become adapted to their environments is natural selection, first described in detail by Charles Darwin and Alfred Russel Wallace. Understanding natural selection requires four connected ideas: variation, overproduction, selection, and inheritance.

Variation within populations

No two individuals in a population are exactly alike. This variation arises from:

• Mutation: Random changes in DNA sequence that create new alleles. Mutation is the ultimate source of new genetic variation.
• Meiosis and sexual reproduction: Independent assortment, crossing over, and the random fusion of gametes shuffle existing alleles into new combinations.

Only variat