Cultural phylogenetics in lowland South America

Comparative phylogenetic analyses based on linguistic data are useful for reconstructing the cultural evolution of recent expansions of humans around the world. It is an exciting time for phylogenetic comparative studies in lowland South America given the emergence of more comprehensive ethnolinguistic datasets. Phylogenetic methods can now be applied to more lowland language families to facilitate the study of pre-historical population expansions and cultural variation. This chapter investigates phylogenetic relationships among the six major lowland South American language families using structural linguistic data. Two cultural traits that are likely to have deep evolutionary histories that extend back to last common ancestors of several large language families include uxorilocal postmarital residence (women continue to live near natal families after marriage) and partible paternity beliefs (conception belief that multiple men can be co-genitors of one child). The Carib-Pano-Tupi-Jê clade is mostly uxorilocal with partible paternity beliefs in thirty-eight of forty-three societies.

Kinship structures create persistent channels for language transmission

Languages are transmitted through channels created by kinship systems. Given sufficient time, these kinship channels can change the genetic and linguistic structure of populations. In traditional societies of eastern Indonesia, finely resolved cophylogenies of languages and genes reveal persistent movements between stable speech communities facilitated by kinship rules. When multiple languages are present in a region and postmarital residence rules encourage sustained directional movement between speech communities, then languages should be channeled along uniparental lines. We find strong evidence for this pattern in 982 individuals from 25 villages on two adjacent islands, where different kinship rules have been followed. Core groups of close relatives have stayed together for generations, while remaining in contact with, and marrying into, surrounding groups. Over time, these kinship systems shaped their gene and language phylogenies: Consistently following a postmarital residence rule turned social communities into speech communities.

A test of the intergenerational conflict model in Indonesia shows no evidence of earlier menopause in female-dispersing groups

Menopause remains an evolutionary puzzle, as humans are unique among primates in having a long post-fertile lifespan. One model proposes that intergenerational conflict in patrilocal populations favours female reproductive cessation. This model predicts that women should experience menopause earlier in groups with an evolutionary history of patrilocality compared with matrilocal groups. Using data from the Indonesia Family Life Survey, we test this model at multiple timescales: deep historical time, comparing age at menopause in ancestrally patrilocal Chinese Indonesians with ancestrally matrilocal Austronesian Indonesians; more recent historical time, comparing age at menopause in ethnic groups with differing postmarital residence within Indonesia and finally, analysing age at menopause at an individual-level, assuming a woman facultatively adjusts her age at menopause based on her postmarital residence. We find a significant effect only at the intermediate timescale where, contrary to predictions, ethnic groups with a history of multilocal postnuptial residence (where couples choose where to live) have the slowest progression to menopause, whereas matrilocal and patrilocal ethnic groups have similar progression rates. Multilocal residence may reduce intergenerational conflicts between women, thus influencing reproductive behaviour, but our results provide no support for the female-dispersal model of intergenerational conflict as an explanation of menopause.