Matrilocal residence is ancestral in Austronesian societies

Abstract

The nature of social life in human prehistory is elusive, yet knowing how kinship systems evolve is critical for understanding population history and cultural diversity. Post-marital residence rules specify sex-specific dispersal and kin association, influencing the pattern of genetic markers across populations. Cultural phylogenetics allows us to practise 'virtual archaeology' on these aspects of social life that leave no trace in the archaeological record. Here we show that early Austronesian societies practised matrilocal post-marital residence. Using a Markov-chain Monte Carlo comparative method implemented in a Bayesian phylogenetic framework, we estimated the type of residence at each ancestral node in a sample of Austronesian language trees spanning 135 Pacific societies. Matrilocal residence has been hypothesized for proto-Oceanic society (ca 3500 BP), but we find strong evidence that matrilocality was predominant in earlier Austronesian societies ca 5000-4500 BP, at the root of the language family and its early branches. Our results illuminate the divergent patterns of mtDNA and Y-chromosome markers seen in the Pacific. The analysis of present-day cross-cultural data in this way allows us to directly address cultural evolutionary and life-history processes in prehistory.

Figure 1

Map of the Pacific depicting locations of 135 Austronesian ethno-linguistic groups, colour-coded by their main residence pattern (blue circles, patrilocal; red circles, matrilocal; black circles, ambilocal). Outlines show the distribution of five high-order language subgroups, corresponding to groups indicated on phylogeny in figure 3.

Figure 2

(a) Posterior distributions of the probabilities (x-axis) of an ancestral state being matrilocal (grey bars) or patrilocal (white bars) for the four high-level subgroups corresponding in figure 3 ((i) PAN, (ii) PMP, (iii) CEMP, (iv) POc). Values given are the mean±s.d. for the distribution. Bars represent the 95% highest posterior density. (b) Posterior distribution of transition rates showing that transitions from matrilocality to patrilocality (qMP, grey bars) take values twice as high as the reverse (qPM, white bars).

Figure 3

Summary phylogeny of 135 Austronesian languages; this is a 50% majority rule consensus tree of all 1000 trees in the posterior (see §2; branch lengths not to scale). Taxa colour depicts a society's residence pattern (red, matrilocal; blue, patrilocal; black, ambilocal). Subgrouping bars (right) correspond to map in figure 1. Numbers above nodes are Bayesian posterior probabilities for that clade (phylogenetic uncertainty, only those above 0.5 shown). Nodes are colour-coded to reflect ancestral states of residence. Filled circles have probabilities of being matrilocal (red) or patrilocal (blue) above 0.7, taking into account both phylogenetic and trait uncertainty. Open circles are where trait reconstruction was above 0.7 matrilocal/patrilocal but when combined with the clade posterior probabilities were below 0.7. All other nodes are above 0.7 for both clade and trait. The four large nodes correspond to the distributions in figure 2 and show the combined probability for the ancestral state. An, Austronesian; MP, Malayo-Polynesian; Oc, Oceanic; SHWNG, South Halmahera–West New Guinea; W, Western; C, Central; E, Eastern; P, proto.