What is Natural Selection

What is natural selection? Darwin’s main contribution was not to establish that evolution occurs, although he helped in that regard. His great achievement was his theory of natural selection. In a nutshell, Darwin’s theory runs as follows:

• There is heritable variation in a population.

• More individuals are born in a population than can survive.

• Individuals that do survive and reproduce are not a random subset of the population. These individuals possess traits that somehow make them better at surviving and reproducing in a particular environment.

• The heritable adaptive traits would become increasingly represented in a population over time, and thus shape the phenotypic characteristics of that population.

There are a couple of additional points. Natural selection can only act on existing heritable variation. If there is no variation for a particular trait, then selection simply cannot do anything with it. This is why the generation of variation in the context of mutation and genetic recombination is so central to our understanding of evolution.

Another important point is that although natural selection acts on individuals, its evolutionary consequences occur in populations. Individuals do not evolve. Evolution is measured as change in the average characteristics of individuals within a population. I think this, in a nutshell, answers the question.

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