Digit ratios predict polygyny in early apes, Ardipithecus, Neanderthals and early modern humans but not in Australopithecus

Emma Nelson, Campbell Rolian, Lisa Cashmore, Susanne Shultz

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Social behaviour of fossil hominoid species is notoriously difficult to predict owing to difficulties in estimating body size dimorphism from fragmentary remains and, in hominins, low canine size dimorphism. Recent studies have shown that the second-to-fourth digit ratio (2D: 4D), a putative biomarker for prenatal androgen effects (PAEs), covaries with intra-sexual competition and social systems across haplorrhines; non-pair-bonded polygynous taxa have significantly lower 2D: 4D ratios (high PAE) than pairbonded monogamous species. Here, we use proximal phalanx ratios of extant and fossil specimens to reconstruct the social systems of extinct hominoids. Pierolapithecus catalaunicus, Hispanopithecus laietanus and Ardipithecus ramidus have ratios consistent with polygynous extant species, whereas the ratio of Australopithecus afarensis is consistent with monogamous extant species. The early anatomically modern human Qafzeh 9 and Neanderthals have lower digit ratios than most contemporary human populations, indicating increased androgenization and possibly higher incidence of polygyny. Although speculative owing to small sample sizes, these results suggest that digit ratios represent a supplementary approachfor elucidating the social systems of fossil hominins. © 2010 The Royal Society.
    Original languageEnglish
    Pages (from-to)1556-1563
    Number of pages7
    JournalProceedings of the Royal Society B: Biological Sciences
    Volume278
    Issue number1711
    DOIs
    Publication statusPublished - 22 May 2011

    Keywords

    • Hominin
    • Pair-bonded
    • Polygyny
    • Prenatal androgens
    • Second-to-fourth digit length ratio
    • Social system

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