VARIATION OF NEUTRAL CHARACTERS IN SUBDIVIDED POPULATIONS (INDIA, NEW GUINEA

Morphological and biochemical variation among human populations has been extensively documented. Most biochemical characters are thought to be selectively neutral, hence their variation reflects only the effects of genetic drift and patterns of mate exchange. The factors conditioning variation in morphological characters are, in general, more complex. This study explores the possibility that the relationship between biochemical and morphological variation may contain information about the factors responsible for variation in morphological characters.;A migration matrix model is used to deal with both biochemical and morphological characters, and several new results emerge. Because genetic drift occurs at reproduction, the differentiation of newborns will be greater than that of their parents. Since most genetic studies pool individuals of different ages, the age distribution of the sample is a potent confounding influence. On the other hand, if separate estimates are obtained for differentiation of adults and children, the difference between them can be used to estimate both the effective size of the population and its level of mobility. These variables are completely confounded in previous population structure statistics.;Previous investigations of the variance of neutral quantitative characters in subdivided populations have ignored the effect of gametic disequilibrium. It is shown here that although the effect of gametic disequilibrium can be quite large, it is zero in expectation. However the variance about this expectation is substantial. If the number of loci is at all large, the effect of variation in gene frequencies is negligible compared to the effect of gametic disequilibrium.;This theory provides a basis for predicting the variance among groups in a neutral quantitative character. Observed and predicted variation are compared in two populations. Variation of dermatoglyphic characters is completely consistent with the neutral model for both the Dhanger castes of Maharashtra, India, and the inhabitants of Bougainville Island, in Papua New Guinea. On the other hand, morphological variation on Bougainville is a good deal larger than the neutral model predicts. It seems clear that something other than drift and migration is affecting the distribution of morphological characters on Bougainville.