Mitochondrial DNA variation is an indicator of austronesian influence in Island Melanesia

Past studies have shown a consistent association of a specific set of mitoc hondrial DNA 9 base pair (bp) deletion haplotypes with Polynesians and thei r Austronesian-speaking relatives, and the total lack of the deletion in a short series of New Guinea Highlanders. Utilizing plasma and DNA samples fr om various old laboratory collections, we have extended population screenin g for the 9-bp deletion into "Island Melanesia," an area notorious for its extreme population variation. While the 9-bp deletion is present in all Aus tronesian, and many non-Austronesian-speaking groups, it is absent in the m ore remote non-Austronesian populations in Bougainville and New Britain. Th ese results are consistent with the hypothesis that this deletion was first introduced to this region about 3,500 years ago with the arrival of Austro nesian-speaking peoples from the west, but has not yet diffused through all populations there. The pattern cannot be reconciled with the competing hyp othesis of a primarily indigenous Melanesian origin for the ancestors of th e Polynesians. Although selection clearly has operated on some other geneti c systems in this region, both migration and random genetic drift primarily account for the remarkable degree of biological diversity in these small S outhwest Pacific populations. (C) 1999 Wiley-Liss, Inc.