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Mechanisms of Evolution



There are multiple mechanisms of evolution (genetic change between generations), but arguably the most important mechanism is natural selection. Natural selection is the idea that individuals with certain traits will survive and reproduce better than other individuals in a given environment. Over time, favorable traits will accumulate in a population, leading toward adaptation to that environment. Charles Darwin is considered the father of evolutionary biology because, in his book On the Origin of Species, Darwin argued that life is ever changing and that natural selection is the primary force driving this change. Distinctions are now made among multiple mechanisms of evolution: mutation, migration, random events, and mate choice. If these factors are not operating in a population, evolution is not occurring. The amount of genetic change in a population is measured by evaluating the gene and genotype frequencies and comparing observations with predictions made by the Hardy-Weinberg Principle.

At A Glance

  • Charles Darwin introduced the idea of evolution by natural selection in On the Origin of Species.
  • Natural selection is a process by which individuals with certain traits survive and reproduce better than other individuals in a given environment.
  • Darwin observed that there is heritable variation (differences based on genes) in traits among individuals and that there is competition for resources. From these observations, he inferred that individuals who are better suited for their environment will be more successful than other individuals, causing their traits to spread in a population over time.
  • Natural selection is the only mechanism of evolution that always leads toward adaptation (better survival and reproduction in an environment).
  • Sexual selection increases the reproductive success of organisms with certain traits.
  • Random genetic drift changes the proportion of a population that has a version of a gene to a greater degree in small populations.
  • Sudden, dramatic reductions in population size can reduce genetic variation by chance; this change in the gene pool is known as the bottleneck effect.
  • The founder effect can change gene frequencies through the random selection of individuals founding a new population.
  • Gene flow can lead to a change in gene frequencies by introducing genetic variation from a neighboring population.
  • The Hardy-Weinberg principle states that in the absence of evolution, gene and genotype frequencies will remain constant.
  • In order for the Hardy-Weinberg equilibrium to occur, there needs to be no mutation, no natural selection, random mating, no genetic drift, and no gene flow within the population.
  • An allele frequency is how often certain genes appear in the population. This is used to calculate whether or not the alleles are changing.