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H.C. Harpending and E. Eller
likely to be belligerent and gaudy: it is in these among technologically primitive
societies where fancy artistic expression occurs as either a manifestation or a sideeffect of male competition. In the former kind of society males are likely to be
occupied working to provision their offspring. Certainly there are many foraging
societies where there is no production of fancy technology like that of Mode 4
cultures. We can compare the drab limited technology of Kalahari Bushmen, for
example, with the rich diversity of weapons and art from central African societies.
The second scenario is that there was a single expansion of moderns out of
Africa. Modern humans reached Australia from southeast Asia much later, and the
old technologies and fossils from Australia, like Mungo and Kow Swamp, are those
of another species of archaics, not of modern humans. This is not a popular scenario today, but it deserves consideration. Under this model the arrival of modern
humans in Australia occurred not 40000 years ago but perhaps 5000 with the appearance of a small tool technology, the dingo, and an apparent tenfold increase in
population (Bellwood 1997).
2.4 Diversity Patterns
Figures 1 and 2 summarize world patterns in microsatellite diversity from two
separate sources: Fig. 1 is based on results from Lynn Jorde's laboratory at the
University of Utah (Jorde et al. 1995), while Fig. 2 is based on results from Kenneth
Kidd's laboratory at Yale (Calafell et al. 1997).
The left panels in each figure show how genetic diversity declines away from
Africa. The horizontal axes are genetic distances from the African mean. The vertical axes are average heterozygosity. The pattern is clear in each case: the more
genetically different a population is from African populations the lower its genetic'
diversity. This pattern is in good agreement with a model of human expansion that
includes series of bottlenecks during colonization episodes in which diversity was
lost. By the time we reached interior South America, according to the evidence of
the Surui of Amazonia, we had lost about one quarter of our neutral genetic diversity.
The right panels in each figure are plots of the leading two principal components of the normalized allele size covariance matrix among populations. This is
the (least squares) best two dimensional picture of genetic distances among populations. In each case we see that there is a general concordance between geography
and genetic distance: neighbors are genetically similar. In Fig. 1 there is apparent
"clumping" into three traditional races: African, European, and Asian, with the
Biaka and Mbuti as slight outliers. This could reflect real differences from other
African popUlations or it could reflect the small number of individuals from each
popUlation in the Jorde data. In Fig. 2 the picture is dominated by the genetic
distinctiveness of small and probably isolated popUlations that have undergone a
lot of gene frequency change due to drift. Compare, for example, the isolated Surui
with the large cosmopolitan Maya.
H.C. Harpending and E. Eller
likely to be belligerent and gaudy: it is in these among technologically primitive
societies where fancy artistic expression occurs as either a manifestation or a sideeffect of male competition. In the former kind of society males are likely to be
occupied working to provision their offspring. Certainly there are many foraging
societies where there is no production of fancy technology like that of Mode 4
cultures. We can compare the drab limited technology of Kalahari Bushmen, for
example, with the rich diversity of weapons and art from central African societies.
The second scenario is that there was a single expansion of moderns out of
Africa. Modern humans reached Australia from southeast Asia much later, and the
old technologies and fossils from Australia, like Mungo and Kow Swamp, are those
of another species of archaics, not of modern humans. This is not a popular scenario today, but it deserves consideration. Under this model the arrival of modern
humans in Australia occurred not 40000 years ago but perhaps 5000 with the appearance of a small tool technology, the dingo, and an apparent tenfold increase in
population (Bellwood 1997).
2.4 Diversity Patterns
Figures 1 and 2 summarize world patterns in microsatellite diversity from two
separate sources: Fig. 1 is based on results from Lynn Jorde's laboratory at the
University of Utah (Jorde et al. 1995), while Fig. 2 is based on results from Kenneth
Kidd's laboratory at Yale (Calafell et al. 1997).
The left panels in each figure show how genetic diversity declines away from
Africa. The horizontal axes are genetic distances from the African mean. The vertical axes are average heterozygosity. The pattern is clear in each case: the more
genetically different a population is from African populations the lower its genetic'
diversity. This pattern is in good agreement with a model of human expansion that
includes series of bottlenecks during colonization episodes in which diversity was
lost. By the time we reached interior South America, according to the evidence of
the Surui of Amazonia, we had lost about one quarter of our neutral genetic diversity.
The right panels in each figure are plots of the leading two principal components of the normalized allele size covariance matrix among populations. This is
the (least squares) best two dimensional picture of genetic distances among populations. In each case we see that there is a general concordance between geography
and genetic distance: neighbors are genetically similar. In Fig. 1 there is apparent
"clumping" into three traditional races: African, European, and Asian, with the
Biaka and Mbuti as slight outliers. This could reflect real differences from other
African popUlations or it could reflect the small number of individuals from each
popUlation in the Jorde data. In Fig. 2 the picture is dominated by the genetic
distinctiveness of small and probably isolated popUlations that have undergone a
lot of gene frequency change due to drift. Compare, for example, the isolated Surui
with the large cosmopolitan Maya.