Geographically isolated populations can also begin speciation simply through random genetic drift . Isolated populations can diverge more quickly if they have differing resources, however, as they adapt through natural selection to their different environments ( ecological speciation ).
12.
Researchers have variously asserted that the cause is random genetic drift, different natural selection pressures in different areas ( the snail often has darker camouflage in woodland, lighter in rough grassland ) with mixing by migration, and balanced polymorphism.
13.
As a capsule summary, nearly every evolutionary theorist agrees that both natural selection and random genetic drift play important roles, but the precise nature of their interaction is controversial . talk ) 14 : 59, 8 May 2014 ( UTC)
14.
"' Neutralist hypotheses "'emphasize the importance of mutation, purifying selection, and random genetic drift . The introduction of the neutral theory by Jukes'own findings, led to a fierce debate about the relevance of neodarwinism at the molecular level.
15.
A slightly deleterious mutation can be defined as a mutation that negative selection acts on only very weakly so that its fate is determined by both selection and random genetic drift . The presence of slightly deleterious mutations is strongly linked to genes that have experienced the greatest reduction in effective population size.
16.
While acknowledging that many mutations are neutral, selectionists attribute changes in the frequencies of neutral alleles to linkage disequilibrium with other loci that are under selection, rather than to random genetic drift . Biases in codon usage are usually explained with reference to the ability of even weak selection to shape molecular evolution.
17.
It's just that, considering the effective population size, the effect is so small that natural selection won't affect the fate of the allele significantly, by definition, a mutation is neutral when its fate is determined by random genetic drift, it's not defined by its effect on phenotype.
18.
The key difference between ecological speciation and other kinds of speciation, is that it is triggered by divergent natural selection among different habitats, as opposed to other kinds of speciation processes, like random genetic drift, the fixation of incompatible mutations in populations experiencing similar selective pressures, or various forms of sexual selection not involving selection on ecologically relevant traits.
19.
The effective population size ( " N e " ) is defined as " the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration . " " N e " is usually less than " N " ( the absolute population size ) and this has important applications in conservation genetics.
