Dr. van Winkle
02-06-2009, 04:30 AM
Changes in allele frequencies of populations can occur as a result of population bottlenecks, inbreeding, or selection at loci critical for survival in certain environments. These can a be outcomes of pestilence, famine, war, climatic changes, and other natural disasters in which a significant percentage of a population is diminished or otherwise prevented from reproducing. The survivors of such events often differ from the older population and it's genetic structure can drift rapidly under certain conditions. Local selection mechanisms reward the best adaption with a higher reproductive success at the expense of less adapted groups.
There are various more specific forms of selection, among these, sexual selection, adaptation to environmental change, intra- and intergroup competition. Furthermore, there are trends which were not caused by selective pressures, at least not originally, but have been the result of coincidences. Genetic drift for instance, to name one of the most important aspects. So some differences might be rather by chance and because of relative isolation but this shouldn't be overestimated in comparison to the results of selective pressure.
Human natural selection is at work when those variants which are smarter than others are favoured, so they can trick the dumber ones through being more effective, idealistic, and better mating success, etc. Contraselection is at work in areas of constant malnutrition, plagues, vitamin and nutrient deficiencies: for example areas in which goitre/struma was common because of iodine deficiency - common in areas further away from the sea or rivers.
A summary of texts written by Agrippa and Schwidetzky (translated from German into English by myself).
There are various more specific forms of selection, among these, sexual selection, adaptation to environmental change, intra- and intergroup competition. Furthermore, there are trends which were not caused by selective pressures, at least not originally, but have been the result of coincidences. Genetic drift for instance, to name one of the most important aspects. So some differences might be rather by chance and because of relative isolation but this shouldn't be overestimated in comparison to the results of selective pressure.
Human natural selection is at work when those variants which are smarter than others are favoured, so they can trick the dumber ones through being more effective, idealistic, and better mating success, etc. Contraselection is at work in areas of constant malnutrition, plagues, vitamin and nutrient deficiencies: for example areas in which goitre/struma was common because of iodine deficiency - common in areas further away from the sea or rivers.
A summary of texts written by Agrippa and Schwidetzky (translated from German into English by myself).