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June 03, 2020, 12:36:01 pm

Author Topic: Genetic drift and natural selection are not speciation  (Read 352 times)  Share 

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Bri MT

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Genetic drift and natural selection are not speciation
« on: October 23, 2019, 06:40:51 pm »

There's been a lot of confusion on this so I thought I'd make a post for everyone to get their confusion & advice in the one place.

Genetic drift changes allele frequency. Natural selection changes allele frequency. Artificial selection changes allele frequency.
All of these are mechanisms of evolution but that does not mean that they are speciation.

E.g. if you have a population and the proportion of alleles coding for long fur long-fur increases this does not make the population a new species or split it into two species.

Situation 1:
If you have populations that are not reproductively isolated, then even though there are changes in allele frequency in each population, the allele frequencies of each population will keep becoming more similar to each other due to gene flow. Therefore, as long as there continues to be no barrier to gene flow between them & random mating, they will keep being the same species as each other.

Situation 2:
If you now introduce a barrier to gene flow then the changes in allele frequency (remember this was already happening!) aren't going to be shared, and thus overtime the populations will accumulate differences in their allele frequencies. For VCE purposes, we consider them to be different species once individuals from the different populations are no longer able to produce fertile offspring together.

In situation 2, but not in situation 1, we see the emergence of multiple species from a common ancestor but in BOTH we have changes in allele frequency.

Sometimes you may also need to refer to mutations as the source of alleles / the ultimate source of genetic variability upon which the mechanisms of evolution may act.

Please feel free to speak up if any of this doesn't make sense or you aren't sure how to apply it :)