Table of Contents
This paper commences with a survey of genetic markers thought to give protection from malaria, in connection with the issue of differentiation between An and NAn populations in Oceania. The closely-linked, highly polymorphic human leukocyte antigen (HLA) class II genes, HLA-DR and -DQ, are then examined for evidence of in situ evolution in some Austronesian-speaking populations of Oceania. The authors define the evolutionary forces of founder effect, genetic drift, mutation, migration and selection and look for evidence that these evolutionary forces shaped the genetic profiles seen in contemporary populations of Austronesian speakers. Genetic data confirm an ultimate East Asian origin for Polynesians but also indicate some degree of past gene flow from island Melanesian populations.
Homo sapiens is an evolving species. We make this point because the archaeological debate relating to the development of Lapita pottery in Melanesia has focused on whether it represents an intrusive culture (Spriggs, this volume) or an indigenous development (Allen and White 1989). This debate has been carried over to the question of whether the pre-Polynesians were a colonizing group from Island Southeast Asia, or a group that evolved within Melanesia. The genetic record shows that contemporary Polynesians do indeed share many genetic features with Island Southeast Asians, but they have also undergone further and probably rapid evolution in the past two or three millennia. That is, in the same way that red-slip decoration of early pottery and vessel forms was shared between Island Southeast Asia and Melanesia (Bellwood, this volume), with a local evolution of Lapita decoration in Melanesia (Spriggs, this volume), contemporary Polynesians have ancestral ties with other Mongoloid populations but also have unique genetic features suggesting further evolution.
In the case of Polynesians, much of the evolution appears to have taken place east of Melanesia, in contrast to Lapita decoration, with the population continuously losing genes on the voyage through the Pacific; not many Polynesian genes have been acquired from Melanesians. This was pointed out 30 years ago by the late Roy Simmons of the Commonwealth Serum Laboratories in Melbourne who noted that Eastern Polynesians lacked the B antigen of the ABO blood group system (Simmons 1962). Those early Austronesians who remained in Fiji and New Caledonia have evolved also, of course, in the sense that the original genetic repertoire has been overlain by Melanesian genetic elements. Western Melanesians in coastal areas have also evolved through genetic admixture with early Austronesian settlers (Serjeantson et al. 1983).
The debate on the origin of the Polynesians has polarized viewpoints, so that the concept of continuing evolution may have been trivialized inadvertently. This has led to criticisms that the geneticists have been studying the wrong populations. That is, if only geneticists would look at the right contemporary populations the missing links would be found. We doubt this. While agreeing there is a frustrating dearth of genetic information for Island Southeast Asia and for the Lapita homeland area in the Bismarck Archipelago, there is substantial evidence that the evolutionary forces of selection, mutation and genetic drift have resulted in the unique genetic profile seen in contemporary Polynesians. Further, the populations from whom the pre-Polynesians derived were also subject to evolutionary forces, as well as to inward migration by other groups. The missing link may not exist and we may need to accept that if, for example, the nine base-pair deletion in mitochondrial DNA (mtDNA) that is almost universally present in Polynesians (Hertzberg et al. 1989) is found also in 18 per cent of East Asians (Stoneking and Wilson 1989), then that is as good a link as we are likely to get. There is simply not going to be an as-yet-undetected population, somewhere in Island Southeast Asia, where everyone tests positive for the mtDNA deletion and negative for blood group B!