Reconsidering the null hypothesis: Is maternal rank associated with birth sex ratios in primate groups?

Gillian R. Brown, Joan B. Silk

Research output: Contribution to journalArticle

96 Scopus citations

Abstract

Trivers and Willard hypothesized that vertebrates adaptively vary the sex ratio of their offspring in response to the mother's physical condition [Trivers, R. L. & Willard, D. (1973) Science 179, 90-92]. This hypothesis has produced considerable debate within evolutionary biology. Here we use meta-analysis techniques to evaluate claims that nonhuman primate females facultatively adjust the sex ratio of their progeny in relation to their own dominance rank in a uniform way. The magnitude of the difference in birth sex ratios of high- and low-ranking females declines as sample sizes increase, and the men difference in birth sex ratios of high- and low-ranking females is zero. These results suggest that the observed effects could be the product of stochastic variation in small samples. These findings indicate that presently we cannot reject the null hypothesis that maternal dominance rank is unrelated to birth sex ratios.

Original languageEnglish (US)
Pages (from-to)11252-11255
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Volume99
Issue number17
DOIs
StatePublished - Aug 20 2002

ASJC Scopus subject areas

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