Can evidence from bioarchaeology and human genetics support the aforementioned archaeological and linguistic interpretations for the expansion of the Fertile Crescent agro-pastoral complex, at least to western Europe, on the one hand, and northern India, on the other? During the early 2000s, mtDNA phylogeographers were using molecular clock calculations to claim that most living Europeans carry indigenous Paleolithic or Mesolithic mtDNA haplogroups. This finding rendered insignificant the impact of any Neolithic migration from Anatolia or the Levant, and much emphasis was placed on postglacial colonization from the presumed refuges in southern Europe that were discussed in Chapter 5.54 It was also widely assumed, as explained by Barbujani and Chikhi (2006), that the molecular clock mutation dates calculated for these haplogroups corresponded to the actual migration dates for the ancestral carriers. No firm reason was ever given to support this assumption, and the molecular clock dates in themselves carried very large ranges of error.
Contrary to these mtDNA molecular clock interpretations, other perspectives have since led to a more favorable approach towards the importance of Neolithic migration into Europe. Mathematical modeling of Mesolithic and Neolithic population histories has generally supported its significance.55 Ancient DNA analysis is allowing geneticists to examine the genetic profiles of ancient people, a very important development since they are no longer entirely dependent on samples from the living, many millennia after the events in question. The Y-chromosome has also come into prominence in recent years as a champion for Neolithic immigration, at least by males, from western Asia into Europe and North Africa.56
Christopher Gignoux and colleagues (2011) have also examined the density of mutation events through time in the whole genomes of mtDNA haplogroups, using the assumption that a major increase in population will increase the frequency of mutation. Their results imply considerable population growth amongst ancestral agricultural as opposed to hunter-gatherer populations, especially during the spreads of food production through Europe, Southeast Asia and sub-Saharan Africa. For Europe, rapid population growth commenced in molecular clock terms around 5700 bc, close to the beginning of the LBK Neolithic in the Carpathian Basin. Although this approach does not necessarily identify the growing populations as immigrant or indigenous, it does reveal that haplogroups identified specifically as descending from Late Paleolithic and Mesolithic populations declined in numbers during and after the cold conditions of the Younger Dryas (11,000-9600 bc).
Perhaps the most thought-provoking observations on human genetic history in recent years have come from the study of ancient DNA.57 In European prehistory, this approach came to prominence in 2005, when mtDNA results from a central European
Neolithic (LBK) population were published with the unexpected conclusion that the lineages represented were neither derived entirely from preceding local Mesolithic populations, nor were they directly ancestral to the majority of modern Europeans. Mystery reigned for a short time, but more ancient DNA results are now available from Spain, France, Germany, Sweden, Austria and Hungary that help to clarify the situation. Unfortunately, none have yet come from the Fertile Crescent itself. But the recent European analyses reinforce the deep separation between Mesolithic and Neolithic populations in Europe, and in most cases between Neolithic and modern populations, with the interesting proviso that a small degree of Paleolithic and Mesolithic mtDNA heritage is still represented in the modern European population as a whole. How to explain this?
Marie-France Deguilloux and collaborators (2012a) interpret these new ancient DNA results as indicating leap-frog migration by small Neolithic populations, emanating in the first instance from the Fertile Crescent or Anatolia, hopping through and over existing European Mesolithic groups, with rather little initial mixing between the two. Most initial Neolithic populations were therefore immigrants, extending along both the Danube and Mediterranean routes westwards and continuing into northwestern Europe. Strontium analyses of the bones of LBK people indicate that they were highly mobile, although this does not mean they or their immediate ancestors all traveled hundreds or thousands of kilometers during their lifetimes directly from the Fertile Crescent. Given that the temperate European Neolithic took over 3000 years to unfold, it is not surprising that a number of mtDNA haplogroups common in the LBK population were not necessarily drawn directly from the contemporary Near East at all, although the absence of ancient DNA from this region must mean uncertainty. However, these mtDNA lineages were not Mesolithic in origin, and it is very unlikely from modern genome studies that they came from the Eurasian steppes. Instead, the Neolithic pioneers of Europe, with their rapidly increasing population sizes,58 probably generated several new haplogroups themselves within European territory as they paused, grew in numbers, and reformulated, often for several centuries, between migratory pulses.
An interesting observation that follows on from this leap-frogging scenario is that, after the Neolithic populations themselves became established, so the rate of admixture with surrounding formerly Mesolithic populations increased. This is perhaps because some of the latter were adopting agriculture and so increasing their own populations around the fringes of the agricultural expansion, hence increasing the all-round likelihood of population contact. The structure here probably resembled that of recent colonial instances of migration in Australia or the Americas, albeit with less adverse initial impact on the indigenous groups. As noted previously, a very similar trajectory occurred with the import of Neolithic domesticated pigs from the Near East into Europe. The first domestic pigs, according to ancient DNA analysis, carried mtDNA haplogroups of Near Eastern origin. But by at least the fourth millennium bc their DNA had become swamped by that of local and formerly wild European pigs.59
The aforementioned reconstruction of European Neolithic prehistory from ancient DNA is supported by recent developments in yet another branch of human biology,
The study of the skeletons of the actors themselves. The most recent and informative of these studies, using craniometric data, suggest again that European Neolithic populations spread from a southeast European or Near Eastern origin by processes of demic diffusion and leap-frogging, initially with little gene flow with Mesolithic populations.60 But, as suggested by the ancient DNA, populations with Mesolithic genetic heritage continued to exist on the Baltic and Atlantic fringes of the continent, and the descendants of these populations eventually contributed to the genetic makeup of modern Europe.
The ancient DNA record of Neolithic expansion is so far confined mainly to Europe, at least within the limits of the Fertile Crescent agro-pastoral complex. Fewer detailed studies are available for regions east of the Fertile Crescent. In the case of South Asia, mtDNA data on living populations support a high degree of indigenous haplogroup origin, especially in the south of the subcontinent, whereas NRY data give stronger support to links with western Asia and Europe, especially for the Indic-speaking populations in the north.61 The NRY data also reveal a very sharp separation between Indian and East Asian populations, the latter including the Tibeto-Burman and Munda (Austroasiatic) speakers of northeastern India (discussed further in Chapter 8), who share with East and Southeast Asians a predominance of NRY haplogroup O.62 Few people crossed the rugged terrain between India and Burma in prehistoric times, apart from the Austroasiatic-speaking ancestors of the Munda and Khasi peoples of northeastern India, who entered that region from Southeast Asia. Even in the Palaeolithic (Chapter 3), this forested region appears to have formed a potential barrier during interglacial climatic phases. The Hindu-Buddhist traders who carried Indic cultural influences to Southeast Asia from 2500 years ago more likely traveled by sea, and only small numbers of these ever settled permanently in their trading locations.
The genetic history of South Asia has been revealed most clearly by whole genome research. As with the NRY and mtDNA data, this also shows very clearly that the modern populations of Pakistan and northern India, especially the Indic-speaking caste populations, are closely related to populations located in the Middle East and Europe. Southern Indian Dravidian-speaking populations, on the other hand, carry more indigenous genetic profiles, albeit with considerable influence from the north. For instance, autosomal SNP (single nucleotide polymorphism) data suggest that Indic speakers introduced between 50 and 70% of the modern genome of northern Indians from western Eurasian sources, but only ~40% of the southern (mostly Dravidian-speaking) genome. Likewise, identification of two major South Asian ancestry components from SNPs reveals one focused in northern India and linked to western Asia and the Caucasus, the other focused in southern India, essentially indigenous to the subcontinent.63 Both of these ancestry components have calculated ages greater than 1500 bc according to admixture modeling, and so predate the Rig-Veda and the end of the Mature Harappan.
Unfortunately, South Asia does not have a great deal of informative skeletal information that reflects on ancient migrations, but dental metric data suggest a degree of continuity in northwestern South Asia from Neolithic Mehrgarh through to Chalcolithic and early historical populations.64 While the craniometric and dental
Evidence is not strong, there is no obvious instance of significant population replacement in Pakistan and northwestern India from the time of Neolithic Mehrgarh (7000 bc) onwards.
World History
