Question

1. How is it possible that in the neutral theory of rate of evolution by genetic drift that population size is unimportant? What differs among small and large populations?

Answer 1

The neutral theory of molecular evolution holds that most evolutionary changes at the molecular level, and most of the variation within and between species, are due to random genetic drift of mutant alleles that are selectively neutral.

The neutral theory allows for the possibility that most mutations are deleterious, but holds that because these are rapidly removed by natural selection, they do not make significant contributions to variation within and between species at the molecular level. A neutral mutation is one that does not affect an organism's ability to survive and reproduce

The neutral theory assumes that most mutations that are not deleterious are neutral rather than beneficial. Because only a fraction of gametes are sampled in each generation of a species, the neutral theory suggests that a mutant allele can arise within a population and reach fixation by chance, rather than by selective advantage

The theory was introduced by the Japanese biologist Motoo Kimura in 1968, and independently by two American biologists Jack Lester King and Thomas Hughes Jukes in 1969, and described in detail by Kimura in his 1983 monograph The Neutral Theory of Molecular Evolution

The proposal of the neutral theory was followed by an extensive "neutralist-selectionist" controversy over the interpretation of patterns of molecular divergence and gene polymorphism, peaking in the 1970s and 1980s

The smaller the population, the more susceptible it is to such random changes. This phenomenon is known as genetic drift. In order to get a better understanding of the potential effect of population size on evolution, it is useful to carry out a simple coin flipping experiment

In larger populations, there is a larger gene pool, meaning that it would take more time for natural selection to show its affect and cause fixation of alleles than in a smaller population