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African Eve, Eurasian Adam

The Age and Origin of the Human Species


Ronald A. Fonda



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 the works cited here) are far longer than new estimates of s. 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 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 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 “African Eve” 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 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 Eurasian origins is the existence of a 200,000 year-old betaglobin linkage common in Asia and rare in Africa (Harding et al., 1997).

The age of the human species has 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 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. Our few thousands of ancestral pairs could have occupied an area as small as Rhode Island and would have faced many natural catastrophes in their long period of isolation.

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 “out of 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 is in doubt, as mtDNA homogeneity may simply show the dilution of mutations caused by recombination.

The putative common source of all human mtDNA 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 is suggestive. As no s. sapiens artifacts have ever been found from more than 60,000 years BPE, the most parsimonious assumption is that humans originated <70,000 years BPE.

As the “Ice-man” reveals, a European type was fully differentiated 7,000 years ago. 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 left that continent. Accordingly (on their view) the time span for conversion to the Eurasian type is only about 50,000 years. I believe it is incumbent upon those who support this view to explain how and why. 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. Perhaps the proponents of an African origin will offer the implausible suggestion that the speciation event itself produced the Eurasian type from African stock; but the view expressed here is that the only logical interpretation of all the available data, including extant populations, is that the speciation event occurred in a Eurasian population, 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 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), evidently interbreeding to produce extant population types. 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 sapiens and erectus traits and their affinities with extant Australian populations.10 We would expect that the skulls 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 to the extent that they acquired near-African diversity. Primitive morphological traits are manifest in the Asian fossil record and in living people.

The hypothesis presented here uniquely explains one particular aspect of the Australian fossil record. The oldest fossils from Australia are the most modern in morphology. On this view, this is explained by the fact that the first humans that 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 which 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 is an unreasonable 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.

The people of the Andaman Islands have also been the subject of a study which has been reported as “supporting the ‘out of Africa.’”11 The data, considered by itself, may not contradict it, 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, was hybridized, and existed in an isolated condition until the present. Not surprisingly, they show genetic affinities to central Africans, because (like them and the S. E. Asians) they preserve substantial portions of the pre-human genome. It is a 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.

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 display a higher level of cognitive function than all 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. Thence we would expect that the 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 Eurasians are cognitively advantaged in comparison to high-diversity populations (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 speak it openly. Only those few whose livelihood is not subject to the fiats of “wimmin and minorities” can openly state the truth on this subject, and even then their views are ruthlessly censored.




Notes


1. Harpending, et al. (1998); see especially the conclusions.

2. & 3. Tishkoff, S. A., from a report in the Science Daily of 25 January 1999 of a presentation at the annual meeting of the American Association for the Advancement of Science in Anaheim on 22 January.

4. Eyre-Walker, ‘Recent Finds in Paleoanthropology’ in Athena Review vol. 2, no. 2 (10 March 2000).

5. See p. 1395 and p. 1399, and generally, to account for the observed diversity clines, which intuitively support radiation out of Eurasia by low-diversity s. sapiens, gaining diversity as they interbred with pre-human populations subsequent to their speciation.

6. Tishkoff, as quoted in Science Daily (above).

7. Tishkoff et al. (1998). On page 1399, she postulates a “dramatic” founder effect and genetic drift.

8. Wolpoff and Milford H. submitted a post entitled “No Homo erectus at Ngandong” to Human Origins News (http://www.proam.com/origins/news/article19.html) on 16 March 2000. He is perhaps the best known proponent of the view that there is continuity between the ancient and modern populations; saying, for instance, that the population represented by the Ngandong specimens is “incontrovertably” ancestral to some Australian fossils and living people.

9. Chang et al. 1996, p. 98 notes the way Melanesians are genetically differentiated from other Pacific islanders and Asians (citing Flint et al. (1993)). Their figures 3 & 5 are somewhat pertinent. Mountain, op. cit., p. 6516, notes clustering of pygmies and S. E. Asians. Figure 1 shows how representative global populations cluster: the pattern is consistent (in the author’s interpretation) with Eurasian hybridization of a species whose genome subsumed the diversity of the current (also hybridized) Africans. Kidd, op. cit. p. 225, cites Harding (1997) concerning variation of betaglobin in S. E. Asians. Jorde, op. cit., Figure 2 shows S. E. Asians clustering with pygmies. Hagelberg (as cited in 11, below) finds affinities between pygmies and Andaman Islanders.

10. Wolpoff’s post (8, above) seems to be in response to the statement of Philip Rightmire (cited as “an expert on the species”) in the 15 December 1996 issue of Human Origins News that “They [Ngandong specimens] are unequivocally H. erectus.”

11. Hagelberg, E. & Fox, C. L. in an unpublished study, quoted in Scientific American, ‘Science and the Citizen,’ January 1999.




References


Awadalla P., Eyre-Walker A., Smith J. M. (1999) ‘Linkage Disequilibrium and Recombination in Hominid Mitochondrial DNA,’ Science vol. 286, pp. 2524-2525 (24 December).

Chang F-M., Kidd J. R., Livak K. J., Pakstis A. J., Kidd K. K. (1996) ‘The world-wide distribution of allele frequencies at the human dopamine D4 receptor locus,’ Human Genetics, 98: 91-101.

Destro-Bisol G., Maviglia R., Caglia A., Boschi I., Spedini G., Pascali V., Clark A., Tishkoff S. (1999) ‘Estimating European admixture in African Americans by using microsatellites and a microsatellite haplotype (CD4/Alu),’ Human Genetics 104: 149-157.

Eyre-Walker A., Smith N. H., Smith J. M. (1999) Proceedings of the Royal Society, London Series B. Biological Sciences 266, 477.

Hagelberg E. et al. (1999) Proceedings of the Royal Society, London, Series B. Biological Sciences 266, 485.

Hammer M. F., Karafet T., Rasanayagam A., Wood E. T., Altheide T. K., Jenkins T., Griffiths R. C., Templeton A. R., Zegura S. L. (1998) ‘Out of Africa and Back Again: Nested cladistic analysis of human Y chromosome variation,’ Molecular Biological Evolution, April 15 (4): 427-41.

Harding R. M., Fullerton S. M., Griffiths R. C., Bond J., Cox M. J., Schneider J. A., Moulin D. S., Clegg J. B. (1997) ‘Archaic African and Asian lineages in the genetic ancestry of modern humans,’ American Journal of Human Genetics, April 60(4): 772-89.

Harpending H. C., Batzer M. A., Gurven M., Jorde L.B., Rogers A. R., and Sherry S. T. (1998) ‘Genetic traces of ancient demography,’ Proceedings of the National Academy of Science, USA, vol. 95, pp. 1961-1967.

Herrnstein, R. J. and Murray, C. The Bell Curve, (1994) Simon and Schuster (The Free Press) Also: Lynn (1991), Zindi (1994), Lynn (1994), Snyderman & Rothman (1987), Jensen (1993), Jensen & Whang (1993).

Jorde L. B., Rogers A. R., Bamshad M., Watkins W. S., Krakowiak P., Sung S., Kere, J. and Harpending H. C. (1997) ‘Microsatellite diversity and the demographic history of modern humans,’ Proceedings of the National Academy of Sciences, USA, vol. 94, pp. 3100-3103.

Kidd K. K., Bharti M., Castiglione C. M., Zhao H., Pakstis A. J., Speed W. C., Bonne-Tamir B., Lu R-B., Goldman D., Lee C., Nam Y.S., Grandy D. K., Jenkins T., Kidd J. R. (1998) ‘A global survey of haplotype frequencies and linkage disequilibrium at the DRD2 locus,’ Human Genetics 103: 211-227.

Mountain J. L. and Cavalli-Sforza L. L. (1994) ‘Inference of human evolution through cladistic analysis of nuclear DNA restriction polymorphisms,’ Proceedings of the National Academy of Sciences, USA, vol. 91, pp. 6515-6519.

Swisher III C. C., Rink W. J., Anton S. C., Schwarcz H. P., Curtis G. H., Suprijo A., & Widiasmoro (1996) Science, 274 (5294), 1870-1874.

Tishkoff S. A., Dietzsch E., Speed W., Pakstis A. J. et al. (1996) ‘Global patterns of linkage disequilibrium at the CD4 locus and modern human origins,’ Science, Washington, March 8.

Tishkoff S. A., Goldman A., Calafell F., Speed W. C., Deinard A. S., Bonne-Tamir B., Kidd J. R., Pakstis A. J., Jenkins T., and Kidd K. K. (1998) ‘A Global Haplotype Analysis of the Myotonic Dystrophy Locus; Implications for the Evolution of Modern Humans and for the Origin of Myotonic Dystrophy Mutations,’ American Journal of Human Genetics, 62: 1389-1402.

Wolpoff, Milford H. A post entitled: “No Homo erectus at Ngandong” to Human Origins News (http://www.pro-am.com/origins/news/article19.html) on 16 March 2000.




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