Abstract:

Kinship terminology is constrained by competing pressures imposed during cultural transmission: kinship systems optimally balance learnability with communicative usefulness. What structural features of kinship terminology evolved to enable this balance? One potential constraint on kinship systems is their lexicon size; fewer terms facilitate learning, more terms facilitate more precise communication. To test whether kinship lexicon size is constrained by evolutionary pressures, we compared the lexicons of 924 kinship systems to randomly permuted baselines. Overall, lexicons are not significantly different than we would expect by chance (z = 0.68): kinship systems have on average 24 terms per 50 relatives compared to 22 in the simulated baselines. However, analysing individual lexicons shows 12% are smaller than chance (e.g. Māori, with 17 terms) and 17% are larger (e.g. Burmese, with 26 terms). To explain why kinship lexicons are more variable than chance, we consider community structure. Languages spoken by larger populations are known to be more communicatively robust, therefore larger populations may have larger, more expressive kinship lexicons. We used phylogenetic comparative methods to explore whether kinship lexicon size co-evolves with community size. Our findings suggest that kinship lexicon size is constrained not by pressures imposed during language evolution, but by cultural change.

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