Extraordinary Population Structure among the Baining of New Britain

This chapter examines with four unlinked loci the extent of divergence between two linguistically related Baining groups in New Britain. Although they are linguistically related and are less than 100 km apart, they are, by a number of measures, surprisingly different genetically. This difference is explained in terms of male and female demographic distinctions. Early comparisons in global and regional mtDNA and NRY diversity indicate comparatively greater overall mtDNA variability, but greater among-group NRY variation. The chapter suggests that the key factor is the larger effective population size of women (since relatively few men contribute to following generations). This distinction could cause an acceleration in the effects of genetic drift, leading to less overall variation, but proportionately more among-group variation. In the Baining study, evidence is found for a much smaller male effective population size. However, the proportion of males who migrate and successfully reproduce appears to be greater than for females. In considering the surprising degree of overall differentiation between these two Baining groups, the effects of drift are paramount, but there remains the question of whether the differences may be due to the residue of ancient lineage sorting.