Natural Selection

Natural selection is the process of microevolutionary change in a population that is caused by selective pressures that occur in its ecosystem. It was first proposed by Charles Darwin and Alfred Russel Wallace, and it has presently developed into one of the major mechanisms of microevolution.

In order for natural selection to occur, six different factors must be assumed regarding the observed population and ecosystem.

  1. To begin, assume all species have immense reproductive potential when unchecked by other factors in their ecosystem.
  2. To add to the first tenet, assume natural resources are limited, which checks the reproductive potential of species.
  3. Lastly in regards to general tenets, assume overpopulation within a population checks the number of offspring that will survive in each generation.
  4. Genetic and heritable variation must exist with regard to the observed population, which is displayed through various phenotypes.
  5. Of the phenotypes mentioned in the fourth tenet, some phenotypes in the population, and thus some individuals in the population who possess a particular phenotype, have a higher relative fitness than others who do not possess the phenotype.
  6. Ultimately, favorable phenotypes and characteristics that exist in the population are more likely to prevail in the successive generation.

Additionally, or in tandem with these assumptions (as many of these criteria overlap with the previous list), four criteria must be identified in order to recognize a trait within a population is evolving via natural selection.

  1. Natural selection may only act on a single trait which possesses variation within the population.
  2. Natural selection may only act on a heritable trait, or one which possesses genetic basis.
  3. It must be assumed that members of the population possess different degrees of fitness.
  4. Assuming the third criterion is true, members of the population that possess a particular phenotype have higher relative fitness than those in the population who do not possess the phenotype.
    • Note that this criterion is identical to the fifth factor assumed above.