Origin of Modern Humans: Interpreting the Molecular Evidence


Patterns of genetic diversity within our species imply that we descended from a small number of ancestors, of the order of several thousands. While early genetic evidence suggested major population expansions in our past, recent data from the nuclear genome are ambiguous.

Keywords: modern human origins; DNA sequence evolution; ancient demography; coalescent theory

Figure 1.

Genealogy of a sample of six genes. The time intervals between coalescent events are those expected in a population of 10 000 reproducing adults that has always been the same size. The top of the genealogy, the coalescent, is at 830 000 years ago.

Figure 2.

Genealogy of a sample of six genes from a population that expanded by several orders of magnitude 100 000 years ago, before which it had 1000 reproducing adult women. This is a plausible model of human mtDNA evolution.

Figure 3.

Genealogy of a sample with an elongated top. This pattern could be produced by a recent decrease in population size as well as by balancing selection. Evidence for elongated tops of human gene genealogies would suggest that the small number of our founders was preceded by a large effective size of Homo erectus.

Figure 4.

Histogram of the number of pairwise sequence differences among 636 human mtDNA sequences at 411 positions of the first HVS1.

Figure 5.

The bars show the number of the less common nucleotide at segregating sites in a sample of 636 mtDNA sequences. The horizontal line shows expected numbers under constant population size. The excess of rare mutants is a signature of population expansion.

Figure 6.

Plausible human mtDNA genealogy of Figure with the mtDNA from two Neanderthals added. The Neanderthal genes are clearly in a different clade. On the other hand, human nuclear genes often coalesce at a million years ago or earlier, so there is not likely to be such a clear separation visible in nuclear genes.



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Harpending, Henry C(Dec 2007) Origin of Modern Humans: Interpreting the Molecular Evidence. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003487.pub3]