South Asia

The debate for this region is really only just starting, compared to Europe. In 1996, Giuseppe Passarino and colleagues published evidence for a "dilution" of an ancient mtDNA marker in northern India by Caucasoid populations coming in from western Asia, thus supporting a demic spread of Indo-Europeans into India. In 2001, Lluis Quintana-Murci and colleagues carried this perspective further with an analysis of Ychromosomes, suggesting two episodes of demic diffusion from the northwest. The first, represented by Y-chromosome haplogroup 9, accounts for 30 to 60 percent of Southwest Asian lineages and -20 percent of those in Pakistan and northern India. This haplogroup is stated to relate to Elamo-Dravidian movement from Iran. The second, represented by Y- chromosome haplogroup 3, is common in central Asia and northern India, and is stated to record the movement of Indo-European speakers. The spread of haplogroup 9 occurred between 4,000 and 6,000 years ago, haplogroup 3 between 3,500 and 4,500. The authors conclude "The geographical distributions, observed clines, and estimated ages of Hg-9 and Hg-3 chromosomes in southwestern Asia all support a model of demic diffusion of early farmers from southwestern Iran - and nomads from western and central Asia - into India, bringing the spread of genes and cultures (including language)" (Quintana-Murci et al. 2001:541).

Support for cultural diffusion models is not lacking in this region, however. Toomas Kivisild and colleagues (2003) claim that the northern Indian Y- chromosome lineages could be more ancient than Quintana-Murci and colleagues suggest, indeed much older than the Neolithic. They allow an estimate of only -8 percent of "Neolithic" lineages in South Asia, thus arguing for only a very small amount of population movement from the west associated with early farmers and Indo-Aryans.

This rather brief review indicates that the conclusions for Asia are no firmer than those for Europe. Can we add more from skeletal anthropology? Brian Hemphill and colleagues (1991) have summarized a great deal of data on Harappan and related skeletal populations, noting a progressive decline in dental health since the early Neolithic, and the possibility of a population

change in terms of non-metric dental characters between 6000 and 4500 BC. They also note that the population resident at Mohenjo-Daro during the Harappan was morphologically different from other Harappan populations. The Harappans as a whole resembled Iranian populations in cranial terms, whereas the older Neolithic population at Mehrgarh resembled that from Chalcolithic Inamgaon in Maharashtra. It is not clear if such observations can be related usefully to questions of Indo-Aryan and Elamo-Dravidian origins, but they certainly do not support any total isolation of the subcontinent since the Paleolithic.

Africa

In 1987, Laurent Excoffier and colleagues noted close relationships between African major linguistic populations and the genetic geography of the Rhesus blood group system, protein systems, and DNA molecules. Bantu-speakers were stated to be fairly homogeneous genetically, and distinct from Afroasiaticspeakers. Southern Bantu populations revealed evidence for past admixture with Khoisan populations. In 1996, Hirnla Soodyall and colleagues suggested that a distinctive mtDNA 9-base-pair deletion, different in origin from a similar deletion found in many East Asian populations, spread widely during Bantu expansion, also being found through admixture in Pygmy populations. The deletion, however, does not occur in other Niger-Congo speakers in West Africa, and so probably originated after Bantu expansion had commenced.

Genetic support for demic diffusion as part of the Bantu spread is thus quite firm. In 1996, Elizabeth Watson and colleagues analyzed African mtDNA sequences to indicate much greater nucleotide sequence variability amongst hunter-gatherer populations than amongst farmers and pastoralists. The results were interpreted to suggest that the farmers and pastoralists (including Bantuspeakers) have increased their population sizes relatively recently, whereas the hunter-gatherers have had stable population sizes. In 1997, Estella Poloni and colleagues showed that Y-chromosome lineage variation is well correlated with language family distributions in Africa and Eurasia. Their Y-chromosome molecular clock calculations suggested that speakers of Niger-Congo languages began to spread around 4,000 years ago, Afroasiatic speakers around 8,900 years ago, and Indo-European speakers around 7,400 years ago.

Poloni et al. also showed that Afroasiatic-speakers in Ethiopia share Y- chromosome haplotypes with people in Southwest Asia, but have essentially local mtDNA lineages. Some Khoisan populations in the south have admixtures of Niger-Congo Ychromosome lineages with Khoisan mtDNA. Both these situations suggest a tendency for males to disperse further than females, and consequently to have a wider genetic impact. This view was given further support in 2001, when Peter Underhill and colleagues (2001 a) indicated that Bantu migration is strongly marked by the distribution of Y-chromosome

haplogroup III, but Bantu mtDNA haplogroups are more localized.

The African genetic data thus seem to agree closely on the significance of Bantu population expansion. For other populations, including Afroasiaticspeakers, the data are not so clear (Barbujani et al. 1994), and research still has rather a long way to go.