Digit ratios predict polygyny in early apes, Ardipithecus, Neanderthals and early modern humans but not in Australopithecus
Emma Nelson1,*, Campbell Rolian2, Lisa Cashmore3 and Susanne Shultz4
Author Affiliations
1School of Archaeology, Classics and Egyptology, University of Liverpool,Hartley Building, Brownlow Street, Liverpool L69 3GS, UK
2Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, 3330 Hospital Drive Northwest, Calgary, Alberta, Canada T2N 4N1
3Centre for the Archaeology of Human Origins (CAHO), Archaeology, School of Humanities, University of Southampton, Highfield, Southampton SO17 1BF, UK
4Institute of Cognitive and Evolutionary Anthropology, University of Oxford,64 Banbury Road, Oxford OX2 6PN, UK
*Author for correspondence (enelson@liv.ac.uk).
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 pair-bonded 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 approach for elucidating the social systems of fossil hominins.
pair-bonded, polygyny, prenatal androgens, hominin, social system, second-to-fourth digit length ratio
Received August 12, 2010.Accepted October 14, 2010.
This Journal is © 2010 The Royal Society
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Emma Nelson1,*, Campbell Rolian2, Lisa Cashmore3 and Susanne Shultz4
Author Affiliations
1School of Archaeology, Classics and Egyptology, University of Liverpool,Hartley Building, Brownlow Street, Liverpool L69 3GS, UK
2Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, 3330 Hospital Drive Northwest, Calgary, Alberta, Canada T2N 4N1
3Centre for the Archaeology of Human Origins (CAHO), Archaeology, School of Humanities, University of Southampton, Highfield, Southampton SO17 1BF, UK
4Institute of Cognitive and Evolutionary Anthropology, University of Oxford,64 Banbury Road, Oxford OX2 6PN, UK
*Author for correspondence (enelson@liv.ac.uk).
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 pair-bonded 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 approach for elucidating the social systems of fossil hominins.
pair-bonded, polygyny, prenatal androgens, hominin, social system, second-to-fourth digit length ratio
Received August 12, 2010.
Accepted October 14, 2010.
This Journal is © 2010 The Royal Society
+++++
