The Forces of Evolution Subtitle The Four Forces

The Forces of Evolution Subtitle

The Four Forces of Evolution Scientists concur that the source of genetic disequilibrium in a population can be traced to one of four forces: • Natural Selection, including Sexual Selection • Gene Flow. • Genetic Drift. • Mutation. * *Not really a “force” per se.

Natural Selection • Natural selection has already been discussed at length. • Sexual selection is also called non-random mating, or assortative mating. Here the discussion moves beyond the effect on secondary sexual characteristics to embrace any characteristics that figure into mate choice. • For probably the vast majority of alleles mating is random as the phenotypic effect of an allele is imperceptible or subtle to a potential mating partner.

Assortative Mating • Positive assortative mating: a pattern detected in mating whereby variation in a trait is seen to confer a mating advantage – e. g. high intelligence in men. • Negative assortative mating: a pattern in mating traceable to variation in a trait that confers a disadvantage – e. g. facial hair in women.

Gene Flow: the movement of genes between populations Mechanisms in human populations: • Immigration. Example: present-day Southern California. • Emigration. Example: Ireland between 1845 -1960. • Fooling Around. Example: Any military conflict.

Gene flow and evolution • In the long term, gene flow prevents speciation from happening. Speciation: the emergence of a new species from an existing population. Speciation depends upon some form of isolation, resulting from a breeding barrier (see Amoeba Sister‘s video on speciation). A breeding barrier, with the passage of time, results in descendant populations of a single species becoming genetically and behaviorally incompatible, hence new species.

This Photo by Unknown Author is licensed under CC BY-SA Homo sapiens is a single species after 200, 000+ years of existence because of gene flow.

Genetic Drift takes several forms: • Bottleneck effect: results from the near extinction of a population. • Founder’s effect: results from a population established in a new region by a few founders

All forms of genetic drift have a single root cause – small populations. The California condor may exemplify bottleneck effect.

Barranquitas Village in Venezuela is an example of founder’s effect. It has the highest rate of Huntington’s disease in the world. https: //www. bbc. com/news/world-latin-america-10952800