The big picture….

Hypothesised dispersal route of coastal people from Africa to southern Asia (and eventually Australia and Melanesia) around 60,000 years ago. We call this "The Southern Dispersal Route". There isn't much evidence for it, but we are working on it!!!

Why a southern dispersal route?

The last decade of research into the origins of modern humans has produced much data in support for a last common ancestral population in Africa in the recent past - within the last 150.000 years. These data derive from both traditional palaeoanthropology - fossils and stone tools, and anthropological genetics - largely based on mtDNA and Y-chromosome studies of living individuals, but also on the basis of human fossils (Stringer, 1989; Klein, 1995; Hammer et al., 2000; Stoneking et al., 2001). Our own work contributed to this growing consensus view of a recent African origin of all humans (Foley and Lahr, 1997; Lahr, 1994, 1996; Lahr and Foley, 1998, 2001; Underhill et al., 2001).

However, since 1992, we have also argued that accepting this model requires a re-consideration of the patterns and processes by which human diversity evolved (Foley and Lahr, 1992, 1997; Lahr, 1994, 1996; Lahr and Foley, 1994, 1998). In other words, if all humans were a single genetic and cultural population 150.000 years ago, how, why, and at what rate did differences evolve. Although differences at the individual level are important, and genetically represent the bulk of human variation (Cavalli-Sforza et al., 1994), the clearest structure to human diversity is at the level of populations - be it in terms of physique (Relethford and Harpending, 1994), or genetic clustering (Watson et al., 1997). Therefore, it is in terms of the evolution of human populations that the questions on human diversification have to be addressed. The literature on the global evolution of human populations, or the mechanisms by which it could have happened, is surprisingly small (Cavalli-Sforza et al. 1994; Fix, 2000; Lahr, 1996), and either focused on one central source of evidence, or on micro-evolutionary issues.

Human populations, specially in the prehistoric past, are intimately linked to their ecology, which in turn is linked to broader biogeographic patterns and processes. Through the integration of the available palaeoanthropological and genetic record of human origins into a biogeographic model of the last 150.000 years, we suggested that the evolution of modern human diversity was strongly shaped by the fact that there could have been more than one dispersal of modern humans out of Africa. This proposal differs from traditional and generally held views on this issue by suggesting that, before the large expansion of modern humans into Eurasia from the Levant, an East African population dispersed by way of the coast along the Indian Ocean Rim, into southeast Asia and from there to Melanesia (Lahr, 1996; Lahr & Foley, 1994, 1998).

What explanatory power does such a Multiple Dispersals Model have? We believe that this model accounts for the timing of first colonisation of Australia/Melanesia (Roberts et al., 1994); that it explains an aspect of southern Asian and Southeast Asian diversity that is shared with Melanesian populations and not other Asian groups (Howells, 1989; Lahr, 1996); it explains the differences between the early Upper Palaeolithic fossil and archaeological record and that of the early Australians (Davidson & Noble, 1991; Foley & Lahr, 1997); and finally, that it explains the degree of diversity, both at a genetic and a linguistic level, observed in island Melanesia.

Where is the evidence for an early Southern Dispersal Route out of Africa? At the time we proposed the model all we had was a biogeographic pattern and lack of evidence linking living and fossil aboriginal Australians and Melanesians to the modern human population that left Africa via the Levant around 48.000 years ago. Since then, two genetic studies have found exclusive links between African and Australo-Melanesian populations (Maca-Meyer et al., 2001; Quintana-Murci et al., 1999).

Why should the evidence be so rare? We believe that these early southern Asian populations, and to some extent also Melanesian ones, would have been assimilated or replaced by later historic events. Furthermore, the rise in sea-levels in the last 10.000 years would have erased much of the record of an early coastal population along the Indian Ocean Rim. Although later dispersals and demographic processes, as well as climatic ones, make it more difficult to find traces of early events in human history, we should be able to find some (because otherwise the model would not have any explanatory power towards a current pattern of diversity).

Refs:
Cavalli-Sforza LL, Piazza A, and Menozzi P (1994) History and Geography of Genes. Princeton: Princeton University Press.
Davidson I, and Noble W (1991) The evolutionary emergence of modern human behaviour: language and its archaeology. Man 26:223-254.
Fix A (2000) Migration and Colonisation in Human Evolution. Cambridge: Cambridge University Press.
Foley RA, and Lahr MM (1992) Beyond out of Africa: reassessing the origins of Homo sapiens. Journal of Human Evolution 22:523-529.
Foley RA, and Lahr MM (1997) Mode 3 technologies and the evolution of modern humans. Cambridge Archaeological Journal 7:3-36.
Hammer MF, Horai S, Kim W, Omoto K, Stoneking M, Park H, and Karafet T (2000) A Y-chromosome perspective on the Jomonese component of the contemporary Japanese gene pool. American Journal of Physical Anthropology:171-171.
Howells WW (1989) Skull shapes and the map. Cambridge, MA: Harvard University Press.
Klein RG (1995) Anatomy, behaviour and modern human origins. Journal of World Prehistory 9:167-198.
Lahr MM (1994) The Multiregional Model of modern human origins: a reassessment of its morphological basis. Journal of Human Evolution 26:23-56.
Lahr MM (1996) The evolution of human diversity. Cambridge: Cambridge University Press.
Lahr MM, and Foley RA (1994) Multiple dispersals and modern human origins. Evolutionary Anthropology 3:48-60.
Lahr MM, and Foley RA (1998) Towards a theory of modern human origins: Geography, demography, and diversity in recent human evolution. Yearbook of Physical Anthropology, Vol 41 - 1998 41:137-176.
Lahr MM, and Foley RA (2001) Genes, fossils and behaviour: when and where do they fit? In P Donnelly and RA Foley (eds.): Genes, Fossils and Behaviour: an integrated approach to modern human origins. Brussels: NATO, pp. 13-48.
Maca-Meyer N, González AM, Larruga JM, Flores C and Cabrera VM (2001) Major genomic mitochondrial lineages delineate early human expansions. BMC Genetics 2: 13.
Quintana-Murci L, Veitia R, Santachiara-Benerecetti S, McElreavey K, Fellous M, and Bourgeron T (1999) Mitochondrial DNA, Y chromosome and human population history. M S-Medecine Sciences 15:974-982.
Relethford J, and Harpending HC (1994) Craniometric variation, genetic theory, and modern human origins. American Journal of Physical Anthropology 95:249-270.
Roberts RG, Jones r, Spooner NA, Head MJ, Murray AS, and Smith MA (1994) The human colonisation of Australia: optical dates of 53,000 and 60,000 years bracket human arrival at Deaf Adder Gorge, Northern Territory. Quaternary Science Reviews 13:575-586.

Was the population that colonised Australia the same that colonised New Guinea and adjacent archipelagos?

The answer is that we do not know. Two models are possible - [a] one population moves from Sunda to Sahul (the two mega continents formed by the glacial drop in sea-levels) very early (~60,000 years), and from there later to NG and Melanesia; [b] the colonisation of southern (Australia) and northern (NG) Sahul occurred through separated events from Sunda, possibly separated in time quite substantially (60,000 versus 40,000 ?). These populations, however, would still share an ancestor in southeast Asia, making them seem closer to each other today than to surrounding Asians.

Early agriculture in New Guinea

Evidence of early irrigation structures has been found in PNG, dating to ~ 9,000 years ago. These are in the Kuk Swamp Tea Plantation with abandoned agricultural field networks evident from air photography (a). The two prehistoric paddle-shaped wooden spades (b) were found during the archaeological excavations at Kuk. The spades are about 300 to 400 years old and are similar to paddle-shaped spades that are still being used in te Baliem Valley of Irian Jaya to scoop out drainage ditches.

Bellwood has argued that there are characteristics in the pots found in the eastern islands of Southeast Asia that allow linking the Lapita pottery (really an Island Melanesia thing) to the ones originally from Taiwan.

Various possibilities of dispersals or periods of increased connectivity in NG!!!!

1. Australian-related languages (60-40 ky BP), now extinct
2. Introduction of Papuan languages
3. Important migration and re-distribution of Papuan languages (10-5/4 ky BP ???)
4. Introduction of Austronesian languages from the west
5. Re-distribution of Austronesian languages from the East towards northwestern New Guinea