Invitation Ulrich Reichard : Presentation in HOPE Symposium 2007: Primate Origins of Human Evolution
Date:2007/11/15 - 2007/11/21
He argued that gibbon social arrangements are more flexible than commonly acknowledged, and that this potential closely allies them with great apes. He presented demographic data of fourteen habituated groups and spanning more than two decades, at Khao Yai National Park, Thailand. Social change occurs regularly for common reasons, i. e. birth, dispersal, and disappearance/death; however in addition, group composition is also impacted by male immigration leading to: (i) a resident male's replacement without altering the group's structure, or (ii) a socio-sexually polyandrous group in which the resident male stays as the female's secondary partner, while the incoming male becomes her primary partner. Investigations of sexual relationships show that females are polyandrous, which is in agreement with recent descriptions of genital swellings that functionally resemble the exaggerated swellings of chimpanzees and some Old World monkeys. These observations reveal important similarities in the social organization and mating system of white-handed gibbons when compared to the flexible association patterns of other apes. Thus, it may be argued that a significant predisposition for social flexibility was a trait already present in the last common ancestor of all apes. His presentation brought about a kind of wonder in a general concept and yielded fruitful discussion on gibbon's social structure.