Reconstructing Human Evolution

There are currently two competing hypotheses about the origins of modern humans: a multiregion hypothesis which states that modern Homo Sapiens evolved from a more archaic form in several regions of the Old World over the course of a million years; and the African replacement hypothesis which says that modern humans arose in Africa 100,000 to 200,000 years ago (Jorde, Bamshad and Rogers 128). The problem is to explain the relative lack of genetic diversity among humans which supports the idea that humans expanded from a small population fairly recently in time. There seems to be more genetic diversity within continental populations than between continental populations, which could be consistent with the multiregional hypothesis.

Because of the high mutational rate of mtDNA and lack of recombination, it is possible to use it to estimate the a

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s ago from Africa, with independent colonization of western Asia and India, down to east Asia. Somewhere around 39,000 to 52,000 years ago, the western Asian branch spread radially, with Caucasians going to North Africa and Europe, India, and north and east Asia. More recent immigrations have made the modern human expansions difficult to trace. Basal mutations are shared by clusters of lineages defined as haplotypes, which are continental or ethnically specific. Three of them comprise the sub-Saharan African lineages, nine comprise almost all mtDNAs of Europe, North Africa, and Western Asian Caucasians. The other 8 lineages cover Asia, Oceania and Native Americans. Complete mtDNA sequencing of 53 humans of diverse origins has confirmed these results. Evidence from mtDNA generally supports the recent African origin for modern humans, but these conclusions have also been criticized because there is a lack of statistical support for them (Ingram). Studies have mainly focused on the polymorphism of a small section of the mitochondrial genome called the D-loop, which makes up about seven percent of the genome. This is because there is a high rate of mutation in the D-loop region so it can be used to resolve differences betw
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Approximate Word count = 1744
Approximate Pages = 7 (250 words per page)

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