In 1858, two men, Charles Darwin and Alfred Russel Wallace, independently proposed a mechanism for evolution. Darwin named this mechanism natural selection. Natural selection requires variation among individuals in a population. In a particular environment, some traits of individuals are more advantageous than others. The individuals with the advantageous traits are able to survive better, and therefore they are also able to produce more offspring. In subsequent generations, there are relatively more individuals with the inherited advantageous traits. In this way, the population changes, or evolves, from one generation to the next.

In the accompanying animation, we examine natural selection in Texas Longhorn cattle.


In the accompanying animation, we examined several examples of natural selection, each of which produces strikingly different results in the level of variation in the population.

The mechanism underlying each is the same: individuals with advantageous traits survive better and therefore are able reproduce more, increasing the frequency of individuals with the advantageous traits in the next generation.

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Textbook Reference: Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory