Age and Origin of the Human Species
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 s. 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 s. 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 s. sapiens' age (Mountain et al.,1994). As a consequence, most 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 S. E. 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 the tiny, original population of s. sapiens.
In fact, we do find that Africans and some S. 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 s. sapiens had been separated from the sub-Saharan Africans' ancestors for longer than our species' lifetime.1 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.2
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 do find.3 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.
The age of the human species had lately been estimated at between 150,000 and 250,000 years, based on studies of mitochondrial DNA. Those estimates were based on the assumption of clonal transmission of the mtDNA, and the cited studies invalidate that (Awadalla et al., 1999; Hagelberg et al., 1999; Eyre-Walker et al., 1999), but we do not know by how much the dates are off. Eyre-Walker has proposed that "Eve" may have lived twice as long ago as current estimates,4 or as long as 500,000 years BPE. If there were bottlenecks subsequent to a mtDNA replacement event, which wiped out older lines, it would seem that the sweep occurred more recently than it really did. Accordingly, new estimates of s. sapiens’ age preclude the possibility that such a replacement event took place in, or marked the origin of, our species.
More than one group of researchers (such as Harpending and Jorde) consider that the data support a "clean sweep" of earlier mtDNA lineages and this has frequently been raised in support of the "Eve/Africa" view. However, such ancient dates for an mtDNA replacement event would be consistent with radiation of pre-human species out of Africa, rather than the origin of s. sapiens. There has never been any reason to assume that the putative female (whose mtDNA is said to be ancestral to that found in all living humans) was, herself, a s. sapiens. The entire basis for the "Eve" hypothesis (that all modern, human mtDNA originated with one woman, or even in one restricted population) is falsified by recent research indicating plural lineages in the mtDNA genome. The putative ‘African Eve’ is probably neither chronologically nor causally related to the origin of s. sapiens.
In this circumstance, it is only reasonable to assume that the date of the human cultural explosion suggests the approximate era of s. sapiens speciation. Research on the Y-chromosome yields an estimate of 59,000 years BPE for the “most recent common [paternal] ancestor”, (Underhill, et al, 2000) assuming no selection and population structure effects. Given that caveat, the -59kyr date fits those of the earliest human cultural remains like a hand in a glove.
About forty thousand years ago, people from central Asia migrated into Europe, and their descendants constitute a majority of the population there today (Semino & Passarina, 2000) so we know what type of people they were. They came from the general area of those earliest human cultural sites, and they shared a genetic marker designated as M173. The population which carried that marker must have existed for some time before their migration began, because derivative forms of it are found in Siberia and the Amerinds, which implies that it was present in their common ancestral population that existed prior to 40,000 years BPE. Again, we have a good idea of what that ancestral Eurasian type was, by inference from the populations it generated, and it seems likely to be as ancient as humanity itself. When was there time, within the human culture period, for evolution of the Eurasian ancestral type from African immigrants? Moreover, the precursors to humanity are all present in Eurasia (from H. ergaster, and heidelbergensis, through archaic sapiens) while no comparable sequence has been discovered in Africa.
Even if, contrary to all the data adduced here, humanity had originated in Africa, it seems contrived to assume that s. sapiens would have immediately migrated from that continent, to leave their earliest known (and all subsequent) cultural artifacts in Eurasia. But if (on the Afro-origins view) they did, why did they evolve into the Eurasian ancestral type? What mechanisms, events, and pressures would conduce to such a change? Why did those other populations, said to be ‘first out of Africa’ (on account of their genetic diversity) such as the Andaman Islanders and tropical S. E. Asian types, not experience any such change? Do the Afro-origin people perhaps agree that the speciation event created the Eurasian type from archaic sapiens? The invocation of "genetic drift" and "founder effect", as used to assert a counter-intuitive interpretation of the diversity gradient (Tishkoff et al., 1998)5, will not serve.
I believe it is incumbent upon those who support the view of s. sapiens origins in Africa to explain how and why they were converted to Eurasian types so quickly. And those who maintain that humans originated long before they began to leave cultural artifacts need to explain why; what changed, that made them really human? Why would humans evolve, long ago in Africa, but only begin to behave like humans once they arrived at northern latitudes: are we back to the climate theory of evolution? The author’s view is that the only logical interpretation of all the available data, including the characteristics of extant populations, is that the speciation event occurred in a Eurasian population, of archaic sapiens, with ancient indigenous roots, in which case it is obvious how s. sapiens' progenitors were sequestered from central Africa.
The current Eurasian populations are lightly pigmented, and that is associated with high latitude species and populations in many other genera. It has often been suggested that the ancient ancestors of the Eurasian types were part of a population that had been resident at high latitudes long enough to manifest the derived characteristic of light pigmentation. On this view we would expect to find that light-skinned people would display low diversity and a distant relationship to central Africans, which is what we find. In fact, the genetic difference between Africans and Europeans is so distinct that the proportion of European admixture in Afro-Americans can be determined with a margin of error of only 0.02 (Destro-Bisol et al., 1999).
Harpending states that the population ancestral to s.sapiens was "small during most of the Pleistocene" and that "the number of our ancestors just before the expansion ('origin') of modern humans was small, only several thousand breeding adults." We can compare this characterization of our ancestral population with the evidence that Africans have always had a large effective population size. It is this incongruity that forces Tischkoff to postulate that the pre-human population was both "isolated from the rest of the African continent" and "somewhere in N. E. Africa."6 Moreover, this would have been for a very long time. Perhaps in Lemuria or Atlantis?
The evidence indicates that humans came from a sparse population in Eurasia; that their diversity was further reduced by the speciation event; that they subsequently expanded in every habitable direction; and that they interbred with the populations they came in contact with, producing extant hybrid populations. Hence Mountain et al. (1994) reports that in the cladistic tree "the European branch is significantly short relative to all other branches," that "the neighbor-joining tree... places the European sample close to the center of the tree with an extremely short branch," and further that "Europeans and northeast Asians are closely related." The first two of these statements are inconsistent with origin and radiation out of Africa while the third does not lend it any support.
Evidence for radiation into Africa was found by Hammer et al. (1998) and Tischkoff et al. (1998) noted such evidence, but the latter went on to suggest that no attention should be paid to it.7 The radiation of low-diversity s. sapiens from Eurasia is also the best explanation for the discoveries, dates, morphology and genetic data in S. E. Asia. There, s. sapiens and erectus lived in proximity for as long as 20,000 years (Swisher et al., 1996). So many of the human fossils from this area and era show a mixed suite of s.sapiens and erectus features that interbreeding is the most plausible interpretation of the data. Many students of fossil morphology have long contended that there is continuity between S. E. Asian Hominid fossils and extant indigenous peoples.8 Genetic data show these populations are distinct from northern Asian populations and of comparable diversity to Africans (Chang et al. 1996).9
The Ngandong specimens, in particular, have occasioned much debate on account of their mixture of s.sapiens and erectus traits and their affinities with Australians.10 We would expect that the crania of such hybrids would show affinities to both species, and that is why these fossils are so hard to classify. Some authorities say they are clearly erectus, while others point to modern traits, and especially that very similar skulls (from overlapping dates) are found in Australia. Moreover, the traits in question occur in the modern population. This is not merely consistent with, but constitutes strong evidence for, the view that radiating, low-diversity s. sapiens interbred with relic erectus populations, thus acquiring the near-African diversity and primitive morphological traits manifest in the Asian fossil record and extant indigenes.
The hypothesis presented here uniquely explains one particularly puzzling aspect of the Australian fossil record. The oldest fossils from Australia are the most modern in morphology. On my view, this is explained by the fact that the first wave of humans who passed through S. E. Asia on their way to Australia were less hybridized with resident erectus populations because they spent less time living among them. Populations that settled Australia later (leaving the Kow Swamp-type skulls) had been living in S. E. Asia for as much as 20,000 years and were far more hybridized in consequence.
Wolpoff accepts that the Ngandong skulls are representative of the population that produced the Kow Swamp-type specimens, and left descendants in the modern population But he explicitly rejects the view, as set forth here, that there was inter-species gene flow, and calls it "unacceptable". This, however, is a socio-political rather than a scientific statement. He does not contend that it isn’t a reasonable construction of the data, but rejects it on grounds of dogma, because of its implication that some modern populations express a more primitive genome. Wolpoff considers that the hypothesis of hybridization is "unacceptable" because it "raises the specter that some human populations can be interpreted to differ from others because they have more genes from an extinct, primitive human species." Thus, according to Wolpoff and other adherents of this doctrine, scientific truths which conflict with their politically-correct "just so" paradigm are outside the bounds of contemplation. It is noteworthy that he is driven to contend that erectus is human (‘true’man) in order to preserve logical consistency … at the expense of common sense.
The people of the Andaman Islands have also been the subject of a study which has been reported as "supporting 'out of Africa.'"11 This is an example of the almost universal, and usually unstated, assumption that there are only two possible hypotheses of human origins: the multi-regional, and African views. If the data conflicts with the multi-regional view it is said to “support” African origin. This not only begs the question, but is arguably deceitful. In this case, the data, considered by itself, may not contradict African origin, but as part of the pattern already noted above, it actually supports the opposing hypothesis presented here. The Andaman Islands are yet another of the places where s. sapiens interbred with a relic erectus population, were hybridized, and existed in an isolated condition until the present. Not surprisingly, they show genetic affinities to central Africans, because (like them, and some S. E. Asians) they preserve substantial portions of the pre-human genome.
It is nonsense to suggest that the first groups of humans "out of Africa" immediately migrated to the ends of the earth (Andamans, Australia, New Guinea, etc...) or that the populations of all such remote places should possess such diversified and similar genomes by chance. The inferred pattern of hybridization is the more parsimonious hypothesis. They are found in these out-of-the-way places because they were driven there by more advanced populations who supplanted such hybrids elsewhere.
Yet another challenge exists to the claim that our species radiated out of Africa. There is a consensus among anthropologists that s. sapiens' cultural artifacts indicate a higher level of cognitive function than any previous species. The technical level and diversity of their tool industry alone would have set them apart. Add to that, whole new categories of behavior: the creation of representative art, the domestication of the dog, etc... Thus, we would expect that populations which were hybridized with predecessor species would be intellectually and cognitively disadvantaged in relation to low-diversity, Eurasian populations In fact, we do observe that (Herrnstein and Murray, 1994), which clearly reveals the direction of species radiation. Expressing this view, however, is likely to attract such vehement abuse that few dare. Only those whose livelihood is not subject to the fiats of "wimmin and minorities" can openly speak the truth on this subject, and their views are ruthlessly censored.