TWO Huan Pop Bottlenecks

W. Amos and J. I. Hoffman
Evidence that two main bottleneck events
shaped modern human genetic diversity
Proc. R. Soc. B (2010) 277, 131–137
Abstract
“There is a strong consensus that modern humans originated in Africa
and moved out to colonize the
world approximately 50 000 years ago. During the process of expansion,
variability was lost, creating a
linear gradient of decreasing diversity with increasing distance from
Africa. However, the exact way in
which this loss occurred remains somewhat unclear: did it involve one,
a few or a continuous series of
population bottlenecks? We addressed this by analysing a large
published dataset of 783 microsatellite
loci genotyped in 53 worldwide populations, using the program
‘BOTTLENECK’. Immediately following
a sharp population decline, rare alleles are lost faster than
heterozygosity, creating a transient excess of
heterozygosity relative to allele number, a feature that is used by
BOTTLENECK to infer historical events.
We find evidence of two primary events, one ‘out of Africa’ and one
placed around the Bering Strait,
where an ancient land bridge allowed passage into the Americas. These
findings agree well with the
regions of the world where the largest founder events might have been
expected, but contrast with the
apparently smooth gradient of variability that is revealed when
current heterozygosity is plotted against
distance from Africa.”