Academic journal article Mankind Quarterly

Age and Origin of the Human Species

Academic journal article Mankind Quarterly

Age and Origin of the Human Species

Article excerpt

The author questions prevailing fashions concerning the origin of Homo sapiens sapiens, and discusses recent evidence which favors the older view that the evolution of Homo to full sapiens status was probably achieved by a small population resident somewhere in Eurasia, from whence descendants of that population may have spread out to other areas of the world where they may have absorbed genes from older, less evolved populations.

Key Words: Homo sapiens sapiens, Homo erectus, mitochondrial DNA, Ngandong man, Australoids

The speciation event that produced Homo sapiens sapiens could not have occurred contemporaneously in more than a very few individuals. It follows that those few Hs.sapiens would have possessed a very restricted sample of the progenitor species' genetic diversity. However, the diversity observed in current populations implies that there were never less than several thousand breeding pairs in the human ancestry (Harpending et al., 1998). Accordingly, the founding Hs.sapiens and their descendants must have interbred with the progenitor species (and perhaps other pre-human populations) in order to preserve the diversity which exists today.

While some changes in the genome must have occurred after the speciation event, the "lifetimes" of the genetic elements considered (in this context and the works cited here) are far longer than new estimates of Hs.sapiens' age (Mountain et al., 1994). As a consequence, most of the current diversity must be the result of interbreeding with pre-human populations. On this view we would expect to see the most hybridized elements of the modern indigenes in those areas where pre-human population density was highest, such as Africa and H.s. in East Asia. Also, we would expect those populations to have the greatest diversity today, because they would preserve more of the pre-human genome, which would have had much more genetic variety than was represented in any, presumably tiny, original population of H.s.sapiens.

In fact, we do find that Africans and some Hs.sapiens E. Asian populations have not only more diversity (Jorde et al., 1997), but central Africans are said to have ancestral genetic elements as well (Tishkoff et al., 1996). It is also clear that the population which gave rise to Hs.sapiens had been separated from the sub-Saharan Africans' ancestors for longer than our species' lifetime.2 This requires the proponents of the "African Eve/Out of Africa" views to posit a segregation of central Africans from the proto-modern population in which speciation occurred. Since they also claim that modern humans originated in and radiated from Africa, Tishkoff (for instance) is driven to suggest that this hundreds of thousand year sequestration was somewhere in N. E. Africa.3

This is an implausible, ad hoc suggestion. By contrast, it is natural to suppose that separation implies the population ancestral to humans was a part of the radiation out of Africa into Eurasia, before the speciation event occurred. If the speciation event took place in Eurasia, we would expect that the descendant population would show a "bottleneck" effect, and that those populations would possess low genetic diversity today, relative to central Africans, which is what we find.4 By contrast, central Africans have always had a large effective population size (Tishkoff et al., 1996), and are characterized by extraordinary diversity (Kidd et al., 1998). Also we would expect that Asians and Europeans would be more closely related to each other than either are to Africans, as is revealed in the discussion of cladistics below. This view also accounts for the existence of the Eurasian types. Yet more impressive evidence for a common Eurasian origin is the existence of a 200,000 year-old betaglobin linkage common in Asia and rare in Africa (Harding et al., 1997) and the "ancient Eurasiatic marker": NRY binary polymorphism M173, whose particular significance is discussed below. …

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