title: Sex ratio effects on reproductive strategies in humans.
abstract: Characterizations of coy females and ardent males are rooted in models of sexual selection that are increasingly outdated. Evolutionary feedbacks can strongly influence the sex roles and subsequent patterns of sex differentiated investment in mating effort, with a key component being the adult sex ratio (ASR). Using data from eight Makushi communities of southern Guyana, characterized by varying ASRs contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men's and women's investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women. Our results support the behavioural ecological tenet that reproductive strategies are predictable and contingent on varying situational factors.
authors.affiliation: Department of Anthropology , University of Utah , Salt Lake City, UT 84112, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Schacht
authors.affiliation: Department of Anthropology , University of California-Davis , Davis, CA 95616, USA ; Graduate Group in Ecology , University of California-Davis , Davis, CA 95616, USA ; Center for Population Biology , University of California-Davis , Davis, CA 95616, USA.
authors.forename: Monique
authors.initials: M
authors.lastname: Borgerhoff Mulder
keywords: Makushi–Guyana; competition; sex ratio; sex roles; sexual selection