Out of Eden: The Peopling of the World (47 page)

Are the various geographical sources of the first Americans suggested by the anthropologists consistent with those indicated by the genetic story? The stories told by mtDNA and the Y chromosome should have more power to resolve such questions. We can now look at all the American founder lines in terms of their individual Asian genetic homelands discussed in
Chapter 6
.

Two or three Asian sources?

In the last chapter I presented a tale of the Great Freeze driving Asians east, south-east, and north-east out of the increasingly inhospitable Mammoth Steppe, the Central Asian upland region north of the Himalayas. I also suggested that there were at least three different sets of peoples in East Asia, with different genes and technologies. First, already resident on the eastern coastline of Asia, and in particular in Japan, were the descendants of the old beachcombers. Second, there would have been the Mongoloids: the Southern Mongoloids in Southeast Asia, and the Northern Mongoloids to the north of the Yangtzi and most likely also inland on the Tibetan-Qinghai Plateau. Finally there were likely to have been North Eurasians spreading over from the Russian Altai and sharing gene types with North and Eastern Europeans. In terms of geographical locations of potential sources for migrations into America, there were correspondingly at least three (see
Figure 7.6
). In Central Asia there were two potential source regions. They overlapped extensively before the ice age, but were roughly represented in the south by the Tibetan-Qinghai Plateau and in the north by the Russian Altai and the southern Siberian steppe. So, there were two genetically, culturally, and physically different groups: mammoth-hunting Upper Palaeolithic West Eurasians to the north-west, and microblade-making, probably incipient Mongoloids to the south. As I mentioned in
Chapter 6
, the former would most likely have made their way east down the Uda River to the Sea of Okhotsk, and then and down the Amur River to Sakhalin, to the north of Japan. The
latter might have moved down the two great rivers of China, the Yangtzi and the Yellow River, towards the coast.

These three Eurasian peoples, with their three sets of genetic markers, stone tools, and distinctive physiognomies, mingled or staked out their territory before the LGM in the relatively temperate Asian coastal region stretching from Japan and Korea north-east to Okhotsk. They were all candidates for the next step into Beringia, and thence to America, before the ice caps slammed the door shut. The question is whether the evidence of the genetic trail supports that sequence. We can take the story of the male line first because it is relatively clear cut.

A north Eurasian source for American males?

Is the picture of regionally diverse genetic origins supported by the Y chromosome story? The answer is no and yes. No, because as far as the Y chromosome is concerned, one line dominates all the Americas. And yes, because, when we look more closely, we shall find that line and its geographical origin injecting a strong element of Asian regional differences into the parallel mtDNA picture, thus supporting multiple sources (see
Figure 7.6
). Furthermore, there are several curious interlopers. The most striking aspect of the male line in the Americas is that over 90 per cent of all modern Native American Y chromosomes derive from one North Eurasian line, Polo (
Figure 7.7
), and that Polo’s branch, as a whole, also accounts simultaneously for 50 per cent of Europeans, has a scattered Siberian tribal representation, and is virtually absent from East Asia and elsewhere.
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Not surprisingly, given the passage of time, most of the subtypes of the Polo line present in Europe are not the same as the American subtypes. This distinction is close to what is found with the mitochondrial X line, in that the split was a long time ago, maybe more than 25,000 years, and the two separated lines have each gone their way, generating more differences as time has gone on. The position is not quite the same as with X, however, since the Polo line is still common in North Asia, was also the main American founder, and is also found in Europe. These findings support a common origin for European and American members of this male line somewhere in North or Central Asia, and a northern route of entry into the Americas. Having looked at the tribal distribution in Siberia, Russian geneticist Tatiana Karafet and colleagues suggested that the Lake Baikal region is the homeland source of the American migration of this marker (although of course high frequency in itself does not identify a homeland). (
Figure 7.6
.) The European–American links do not stop there. The dominant European subgroup of the Polo line, Ruslan, accounting for 30 per cent of Europeans, is also found among Native Americans at a rate of 12 per cent, higher than could be explained by recent European admixture. North Asia also holds the Ruslan root type, and thus could have been the source of the American Ruslan founder.
⁶⁵

Figure 7.6
   Possible Asian sources of American founder lines. The ‘Venn’ approach rather than precise mapping is used to emphasise the ultimate genetic sources of American lines from three overlapping ancient ethnic groups, the original Pacific Rim beachcombers, the Mongoloids and the Upper Palaeolithic Eurasian hunter-gatherers.

Figure 7.7
   The American Y-chromosome tree. While the bulk of Native American Y chromosomes derive from Polo’s son Quetzalcoatl, scattered other North Eurasian Seth offspring are represented. In contrast to the mtDNA picture, the solitary Cain founder is the only male hint of any provenance from further south or east in Asia.

Far commoner in America than the Ruslan line is a direct branch derivative of the Polo root, Q – which I shall call Quetzalcoatl after the mythical feathered serpent. Quetzalcoatl and his sons account for 64 per cent of American Y chromosomes and are almost unique to the Native Americans. The only exceptions to this last statement found so far are three Siberian Inuits; and one individual each from a neighbouring Siberian group, the Chukchis; the ‘Even’ tribe, an isolated group farther south on the Siberian Pacific coast; the Manchu (of Manchuria); and the Uzbeks from Central Asia. The exceptions all share the special American Y-chromosome type Quetzalcoatl. Since Quetzalcoatl is found among the Na-Dene and the Inuit-Aleut, it is most likely that this American Y marker arose very early on, perhaps even before the founding colonists entered North America before the last ice age. In other words, Quetzalcoatl is a true founder line and not a first-generation derivative. Such a view is supported by dating of the Quetzalcoatl marker in America, which comes out at 22,000 years ago.
⁶⁶

Another North Eurasian Y line that is found very rarely in Native Americans is the TAT type. Although it could have been a post-Columbian European admixture, a North Asian source is still statistically more likely.
⁶⁷

This overwhelming dominance of North Eurasian Y lines in America might seem to point to a single southern Siberian source of Native Americans, and knock multiple migrations out of play. But we should remember that the Y chromosome is much more prone to drift than is mtDNA. Another way of putting this is to say that in many traditional societies, a few of the men tend to father many of the children, whereas the women tend to have more equal numbers of children. This enhanced drift effect is most likely why American Y-line types seem so lopsided.

There is, however, a remaining American Y founder who is more likely to have come from farther east than southern Siberia, and from a beachcomber rather than a Central Asian hunter source. This is the Cain beachcomber line, which spread round the Indo-Pacific coast soon after the movement out of Africa and is identified by an extra mutation, M217. While this Cain line is present throughout North and East Asia, his highest frequencies are found nearer the Pacific coast, in Manchuria and Okhotsk, around the lower Amur River. He is present at 10 per cent or more right down to Southeast Asia (see
Figure 4.5
). With his beachcombing history, this Cain could be the Y type that matches the B mtDNA marker in its more southerly Asian origin (see below).
⁶⁸

Maternal lines from other parts of Asia

The geographical origins of the maternal American founders are more diverse than the male lines, particularly with respect to the mtDNA B group, which is derived from Southeast Asia and is absent from the regions of North Asia most favoured for American Y sources. This spread of geographical sources of migrants supports the view that there were several founding sources for the New World.

In the last chapter I mapped the distribution in Asia of the five American maternal genetic founder lines. Group C is found north of the Himalayas in Asia, and A is far commoner in north-east Asia than further south, so we should look north of the Himalayas for source populations for the peopling of the Americas with these two lines. Group C is widespread in this region, extending from Tibet in the south nearly as far west as the Urals, where it has its highest frequency among the Sel’kups, hunters and fishers who live near the lower Yenisei River, within the Arctic Circle. On the Asian Pacific coast and farther south, C has a much lower frequency. As I explained in
Chapter 6
, the effects of the last ice age would have produced bottlenecks and re-expansions, so gene frequency on its
own may not tell us the exact site of a homeland. However, given that the only parts of northern Central Asia we are certain remained occupied throughout the last ice age were Lake Baikal and the Upper Yenisei River areas of southern Siberia, this seems as likely a region as any for the homeland source of the American Group C (see
Figure 7.6
).
⁶⁹
Group A, on the other hand, coming ultimately from South China, perhaps up the Yangtzi to the Qinhai Plateau, is uncommon in Central and North Asia, with the exception of the extreme northeast of Siberia, where it is the main type. Since this part of Siberia was also part of Beringia, and closest to North America, and since it was A that re-expanded in Beringia after the LGM, north-east Siberia seems to be the most likely immediate Asian source of American Group A. As we saw in
Chapter 5
, the ultimate origin of C was probably India and Pakistan, via the western end of the Himalayas. Group C is a key candidate for the eastern maternal marker of the Upper Palaeolithic peoples who ranged from France to Manchuria before the last ice age. Those hunters may have contributed their skills to the pre-glacial ancestors of the big-game, Clovis-point hunting cultures of North America, which expanded after the ice age.

Like C, the American X line is also likely to have a more northerly Eurasian origin (
Chapter 5
), but because of the large X-free gap between Europe and America, where she is absent, her actual source regions for the peopling of the Americas is a puzzle. The X line has recently been unambiguously identified in North Asia among Altaic peoples of southern Siberia, suggesting a possible homeland (see
Figure 7.6
). The 30,000-year-old link with Europe strongly suggests that X moved across the Asian steppe with Upper Palaeolithic hunters as a low-frequency shared Caucasoid component in the peopling of the Americas, and subsequently nearly became extinct in Asia. Group D is another of the five American maternal founder lines which is common in north-east Asia today. Group D’s ancestor, on the other hand, could have come into North Asia from Southeast
Asia, south of the Himalayas. Its present distribution all along the East Asian Pacific coast, as far south as southern China, suggests a mainly coastal route north.
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