New research suggests that the more competition a fellow has to deal with, the more flamboyant he gets. Or at least that’s the case in primates, according to an international group of researchers led by The University of Western Australia’s Dr Cyril Grueter.
In a paper published online in Evolution and Human Behavior, Dr Grueter and his colleagues investigate the hypothesis that in big, multilevel societies, male primates have developed more ostentatious ‘ornaments’ or ‘badges’.
These include the elongated noses of proboscis monkeys, cheek flanges in orang-utans, capes of white and silvery hair in hamadryas baboons, reddened chests in geladas, upper-lip warts in golden snub-nosed monkeys – and beards in humans.
At least some of these badges may enhance male sexual attractiveness to females – male rhesus macaques with darker red faces receive more ‘come-ons’ from more females during the mating season.
And, male-male competition could even be a stronger reason for the evolution of badges than female choice. For instance, men with beards could be seen as more aggressive and dominant than those without beards – and might also be attractive to women drawn to seemingly powerful men.
In their investigation of 154 species of primates representing 45 genera, the authors found more conspicuous badges in males of species in multilevel social organisations where social and physical conflict were common and individual recognition was limited.
The authors suggest the flamboyant badges were of benefit to males in large and complex social organisations to signal their identity, rank, dominance and attractiveness.
Species that live in smaller groups, on the other hand, had less need of badges as individual recognition and more frequent interactions allowed animals to better assess the social status, strength and quality of their contemporaries.
“When you live in a small group where everyone knows everyone because of repeated interactions, there is no need to signal quality and competitiveness via ornaments,” he said. “In large groups where individuals are surrounded by strangers, we need a quick reliable tool to evaluate someone’s strength and quality, and that’s where these elaborate ornaments come in. In the case of humans, this may also include phenotypic extensions such as body decoration, jewellery and prestige items.”
The authors explain that primate group-sizes vary dramatically: Bornean orang-utans are non-gregarious, whereas mandrills move in hordes of up to 800 animals.
In their paper, the authors argue that the popularity of moustaches and beards among British men from 1842 -1971 rose when there were more males in the marriage pool and beards were judged to be more attractive.
Dr Grueter is the lead author of Are badges of status adaptive in large complex primate groups? The co-authors are Dr Karin Isler from the University of Zurich and Dr Barnaby Dixson of the University of New South Wales.
Video and audio available here.
Dr Cyril Grueter (UWA School of Anatomy, Physiology and Human Biology) (+61 8) 6488 8643 / (+61 4) 06 619 556
David Stacey (UWA Media and Public Relations Manager) (+61 8) 6488 3229 / (+61 4) 32 637 716