Forwarded message:
Date: Sat, 23 Aug 1997 10:18:44 -0700 From: Tim May <tcmay@got.net> Subject: Re: lack of evolutionary pressures
Bluntly put, it ain't going _anywhere_, at least not very fast. Changes in the characteristics of a species, loosely speaking, "evolution," happen faster in small populations.
Actualy this premise is false. The results of evolution stand out more in smaller populations because a given change can propogate through the population with less chance of being swammped by other changes that are also propogating through that population. There is also the fact that the vast majority of changes are either harmless or else debilitating further slowing the genetic drift. Look at it this way. If we have 1000 mating pairs and one of those pairs progeny has a genetic change it is much easier for that change to get propogated because the odds of the offspring mating with the other 999 pairs offspring are much higher than if there were say 10,000 pairs. The number of generations required for that change to become ubiquitous in small populations is much lower than in larger populations. The genetic drift for a given species is usualy low because of this dillution whereas if a punctuating event occurs it will lower the available pool of mates and hence the relative changes increase until the new population becomes stable, usualy because the mitigating effects of the punctuating event have receded. If you would like a concrete case to study, review the research about genetic drift in monkey populations in the Great Rift Valley in Africa. ____________________________________________________________________ | | | Participation requires more than just bitching! | | | | _____ The Armadillo Group | | ,::////;::-. Austin, Tx. USA | | /:'///// ``::>/|/ http:// www.ssz.com/ | | .', |||| `/( e\ | | -====~~mm-'`-```-mm --'- Jim Choate | | ravage@ssz.com | | 512-451-7087 | |____________________________________________________________________|