The use of strontium isotopes as an indicator of migration in human and pig Lapita populations in the Bismarck Archipelago, Papua New Guinea

This paper examines the potential use of strontium isotopes (⁸⁷Sr/⁸⁶Sr) for identifying migration within Lapita populations and their commensal animals, specifically the pig (Sus scrofa). Lapita people (ca. 3300-2200 BP) were the initial colonists of the island groups to the east of the Solomon Islands, spreading from Papua New Guinea to Tonga and Samoa within a few centuries. Mobility is assumed to have been an important mechanism for maintaining cultural solidarity between Lapita communities. It has been previously argued that Lapita populations became progressively more sedentary over time after the initial colonising events. Two Lapita sites, Kamgot and Balbalankin, from the Anir Islands in the Bismarck Archipelago are included in the analysis and fall within the Early (ca. 3300-3000/2900 BP) and Middle (ca. 3000/2900-2700 BP) Lapita periods respectively. Ten tooth enamel samples from Lapita human and pig teeth as well as modern teeth were analysed for strontium isotopes. The mean values for the individuals from both sites were higher than the geological value obtained for the Anir Islands reflecting the incorporation of marine-derived strontium into their tooth enamel taken up in their diet. Although the sample sites have similar environments there was a difference between the local ranges of the strontium isotopic data. One Lapita age pig and one potentially modern pig from Kamgot fell well outside the local distribution for the site and were considered to be non-local. The extreme distribution of the two outliers suggests they came from two geographically separate locations. The results from the Anir Islands when compared with strontium results from other prehistoric Pacific Island populations suggest there is sufficient variation between island groups in terms of the biologically available strontium to justify further research. The present results are discussed in terms of using pigs as a proxy for human mobility as well as an indicator for the 'local' range of an archaeological population by treating human and pigs as separate populations. Strontium isotopes therefore provide the opportunity to investigate migration in Lapita populations on a finer scale than was previously possible.