Interpreting hominid behavior on the basis of sexual dimorphism

doi:10.1006/jhev.1996.0096

Journal of Human Evolution

Volume 32, Issue 4, April 1997, Pages 345-374

https://doi.org/10.1006/jhev.1996.0096 Get rights and content

Abstract

Numerous studies use estimates of sexual dimorphism in canine tooth size and body weight to support speculation about the behavior of australopithecines. However, the range of mating systems inferred for australopithecines encompasses virtually the entire spectrum of mating systems seen among extant anthropoid primates, from monogamy to polygyny characterized by intense male–male competition. This variety of opinion can be attributed partly to the unusual combination of high body size dimorphism and reduced canine dimorphism in australopithecines. Here we provide a joint comparison of recent models for the behavioral correlates of both canine dimorphism and body size dimorphism, and apply this to published estimates of dimorphism in body size and canine tooth size in hominids. Among extant species, body weight dimorphism and canine dimorphism are strongly correlated with estimates of intrasexual competition. Canine crown height dimorphism provides the best discrimination between taxa that show high degrees of male–male competition, and those that do not. Relative male maxillary canine tooth size offers additional evidence about male–male competition. On the other hand, canine occlusal dimorphism offers little discrimination among species of different male–male competition levels. Estimates of canine dimorphism, relative canine size, and body weight dimorphism in australopithecines provide little definitive information about male–male competition or mating systems. Dimorphism ofAustralopithecus africanusandAustralopithecus robustuscan be reconciled with a mating system characterized by low-intensity male–male competition. The pattern of dimorphism and relative canine size inAustralopithecus afarensisandA. robustusprovides contradictory evidence about mating systems and male–male competition. We review a number of hypotheses that may explain the unusual pattern of dimorphism ofA. afarensisandAustralopithecus boiseibut non-satisfactorily resolves the problem given current data.

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Sexual dimorphism of body size in an African fossil ape, Nacholapithecus kerioi

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Citation Excerpt :

Sexual dimorphism of BM and canine size is actually influenced by multiple factors in addition to social structure, such as predation, substrate preference, phylogeny, reproductive strategy, foraging, and diet (Leutenegger and Kelley, 1977; Leutenegger and Cheverud, 1982; Gaulin and Sailer, 1984; Plavcan and van Schaik, 1992; Plavcan, 2001, 2011, 2012). For example, terrestrial primates are generally more dimorphic than closely related arboreal species, which has been explained as a consequence of selection for larger male size associated with male predation-defence (Clutton-Brock et al., 1977; Harvey et al., 1978; Leutenegger and Cheverud, 1982; Cheverud et al., 1985; Plavcan and van Schaik, 1997). Females are generally more responsive to nutritional resource insufficiency than males owing to the higher energetic burden of reproduction (Ralls, 1976; Emlen and Oring, 1977; Wrangham, 1980; van Schaik, 1989; Isbell, 1991; Mitchell et al., 1991; van Hooff and van Schaik, 1992; Isbell and Pruetz, 1998) and such pressure would also influence female body size evolution (Gordon, 2004).

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Citation Excerpt :

This low level of dental size variation does not hint at a high degree of size dimorphism and is consistent with observations from other hominin samples (e.g., Leutenegger and Shell, 1987; Suwa et al., 2009). This is unlike the pattern observed in Australopithecus, where low canine size dimorphism is coupled with high body size dimorphism (Plavcan and van Schaik, 1997; Kimbel and Delezene, 2009; Plavcan, 2012a). Although both the ISD and CV estimates calculated for H. naledi are influenced by small samples and the sex composition of the Dinaledi sample, their combined results conservatively indicate that there is no evidence for strong body size or dental size dimorphism in this assemblage of H. naledi.

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^f1: J. Michael Plavcan

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Regular Article Interpreting hominid behavior on the basis of sexual dimorphism

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Regular Article
Interpreting hominid behavior on the basis of sexual dimorphism