Science continues its occasional series on individuals who make an impact on the progress of science with a review of the growing number of Africans working at the forefront of human evolutionary studies (Gibbons, A. 2003. Africans begin to make their mark in human-origins research. Science, v. 301, p. 1178-1179). Ethiopians, Kenyans, Tanzanians and Eritreans have all made important finds and published their results over the last decade. Their hallmark is avid field work, backed up with growing interpretative skills. All credit the encouragement they have had from western colleagues, but now they are in a position to bring along a new generation of experts in their home countries.
The “Big Daddy” theory of human evolution!
One of the anthropological shocks of the 21st century was the discovery that the gene pool of central Asian men is dominated by such a limited range of Y-chromosome characteristics that the only conclusion is that one small group of closely related men dominated impregnation across the region about 800 years ago. They were probably all Mongols closely related to Genghis Khan (see, Darwinian evolution of humans challenged by Y-chromosome data? EPN March 2003). Studies by geneticists from Italy, Portugal and Spain recently suggested that sexual dominance by very few men may have been widespread before about 18 to 12 thousand years ago, around the beginning of the warming that closed the last glacial epoch (Dupanloup, I. et al. 2003. A recent shift from polygyny to monogamy in humans is suggested by the analysis of worldwide Y-chromosome diversity. Journal of Molecular Evolution, v. 57, p. 85-97). Mitochondrial (passed maternally) and Y-chromosome (paternal) DNA studies have been key tools in explaining the timing of migrations of humans over the last 100 thousand years, since their genetic patterns seem to cluster regionally. Molecular clock estimates that use the appearance of new genetic mutations indicate the timing of population separations. The study by Doupanloup and colleagues examined data from individuals who live on all continents. There is an odd and generally distributed difference in genetic diversity between mitochondrial and Y-chromosome DNA, which superficially suggests far more women than men during the last glacial epoch. In terms of births, that is clearly impossible. One explanation, favoured by Doupanloup et al., is widespread polygamy that dwarfs that which notoriously occurs within some religious sects today. Moreover, the “privilege” would have had to be passed on to successive generations of men directly related to the original “Big Daddies”. Rapid shifts in power would not have left such a clear imprint on global Y-chromosomes. How that was achieved without repression or slaughter of potentially competing men, is impossible to judge. However, probable changes in EuropeanY-chromosome patterns around 70, 40 and 20 thousand years ago, that have been ascribed to either evolutionary “bottlenecks” during periods of rapidly dwindling numbers or sudden migrations, might equally have been due to the rise of new patterns of a few males’ dominance over others. Dupanloup et al. show that the rise of agriculture around 10 thousand years ago seems to coincide with a breakdown of massive polygamy and more common monogamy. There are other possible interpretations of the data. In a largely monogamous society, if males stayed where they were born while women moved to live in their mates’ home area, men would be closely related to others in their area, eventually resulting in very similar Y-chromosomes being shared by many. Different migration patterns or early deaths for most men while hunting may also have led to the genetic bias that is causing great discussion among evolutionary geneticists.
Source: Bhattacharya, S. & Le Page, M. 2003. A few prehistoric men had all the children. New Scientist, 6 September 2003, p. 18.