THE ERECT PENIS IS A FLAG OF SUBMISSION IN A FEMALE-DOMINATED SOCIETY- GREETINGS IN SERENGETI SPOTTED HYENAS

In East Africa, spotted hyenas live in large clans in a highly structu red society dominated by females. A clan is a fission-fusion society w here members are often solitary or in small groups. Spotted hyenas hav e a ritualized greeting during which two individuals stand parallel an d face in opposite directions. Both individuals usually lift their hin d leg and sniff or lick the anogenital region of the other. The unique aspect of greetings between individuals is the prominent role of the erect 'penis' in animals of both sex. Female spotted hyenas have fused outer labiae and a 'pseudo-penis' formed by the clitoris which closel y resembles the male penis and can be erected. During greetings subord inates signalled submission with gestures which were not necessarily r eciprocated by the dominant participant. Asymmetries were most pronoun ced in greetings between adult females where the probability of asymme tries increased with the divergence in rank between partners. Greeting s between adult females and males were uncommon and restricted to male s above median rank, principally the alpha male. Models of primate aff iliative behavior assume that benefits derived from social relationshi ps with different individuals are not equal and that individuals are s elected to maximize the benefits they receive from social relationship s with others. The observed distribution of greetings between partners of different rank matched the predictions of these models. An examina tion of non-adaptive hypotheses on the evolution of the 'pseudo-penis' demonstrated that the conventional scenario linking (initial) viriliz ation of female genitalia with selection for female dominance does not explain either the initial virilization, nor the evolution of the 'ps eudo-penis' to its current form and use. We sketch a new scenario that links (1) initial virilization to the occurrence of neonatal siblicid e amongst members of a twin litter, and (2) costs of maintenance, 'pse udo-penile' control over copulation and male submission. Our analysis confirms previous adaptive hypotheses on the function of the 'pseudo-p enis' in greetings and suggests new hypotheses to account for hitherto unexplained features.