Cooperation beyond consanguinity: post-marital residence, delineations of kin and social support among South Indian Tamils

Abstract

Evolutionary ecologists have shown that relatives are important providers of support across many species. Among humans, cultural reckonings of kinship are more than just relatedness, as they interact with systems of descent, inheritance, marriage and residence. These cultural aspects of kinship may be particularly important when a person is determining which kin, if any, to call upon for help. Here, we explore the relationship between kinship and cooperation by drawing upon social support network data from two villages in South India. While these Tamil villages have a nominally male-biased kinship system (being patrilocal and patrilineal), matrilateral kin play essential social roles and many women reside in their natal villages, letting us tease apart the relative importance of genetic relatedness, kinship and residence in accessing social support. We find that people often name both their consanguineal and affinal kin as providing them with support, and we see some weakening of support with lesser relatedness. Matrilateral and patrilateral relatives are roughly equally likely to be named, and the greatest distinction instead is in their availability, which is highly contingent on post-marital residence patterns. People residing in their natal village have many more consanguineal relatives present than those who have relocated. Still, relocation has only a small effect on an individual's network size, as non-natal residents are more reliant on the few kin that they have present, most of whom are affines. In sum, marriage patterns have an important impact on kin availability, but the flexibility offered by the broadening of the concept of kin helps people develop the cooperative relationships that they rely upon, even in the absence of genetic relatives. This article is part of the theme issue 'The evolution of female-biased kinship in humans and other mammals'.

Keywords: kinship; networks; post-marital residence; relatedness; social support.

Figure 1.

The kinship networks of Aṉakāpuram ((a) N = 440) and Teṉpaṯṯi ((b) N = 344). Nodes (individuals) are coloured by caste. Edges are coloured by the nature of the kinship relationship.

Figure 2.

Distributions of the number of resident kin and of the number of kin named as providing support, for four groups of kin (consanguineal, affinal, matrilateral and patrilateral) broken out by gender and natal/non-natal residency, for all survey respondents in Aṉakāpuram and Teṉpaṯṯi. Numbers in the upper right of the plots give the mean and per cent of zeroes for the overall distribution in each plot.

Figure 3.

The social support networks of Aṉakāpuram ((a) N = 440) and Teṉpaṯṯi ((b) N = 344). Nodes (individuals) are coloured by caste. Edges are directed, with arrows pointing to the individual asked for support. Node position is determined by the Fruchterman–Reingold algorithm.

Figure 4.

(a) Odds ratios (with 95% confidence intervals) for natal versus non-natal ever-married residents for having relatives of various types residing in the same village (‘co-resident’ kin type), for having named others as support partners (named support), and for having named relatives of various types as support partners (‘named’ kin type), for each village, based on simple Poisson and binomial regressions (see electronic supplementary material, tables S10 and S11). (b) Violin and dot plots showing the number of co-resident consanguineal relatives (top), named support partners (middle) and named affinal kin (bottom, specifically spouse’s consanguineal relatives) for natal and non-natal ever-married residents of Aṉakāpuram.

Figure 5.

Odds ratios (with 95% confidence intervals) for the variables of interest across each of the main ERG models, for each village.