"If the misery of the poor be caused not by the laws of nature, but by our institutions, great is our sin."
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Feb 26, 2007

American Journal of Physical Anthropology, 2007, 132(S34): 137

Lack of inbreeding avoidance and reduction of alliance formation in matrilineally-housed bonobos (Pan paniscus).

E.M. Johnson
Evolutionary Anthropology Graduate Program
Washington State University


Wild bonobo females transfer at sexual maturation into groups without kin. Non-related females perform GG rubbing and grooming to form alliances, and females may mate indiscriminately without risk of incest. The present study investigated social dynamics of a captive bonobo group with a matrilineal core: three adult sisters, their offspring, and an unrelated adult male. It was predicted that these females might demonstrate reduced alliance formation with one another as measured through time spent in proximity and GG rubbing, and that incest might occur because females were housed with their sister's adult sons. 79 hours of 10-minute focal animal samples were collected at San Diego Wild Animal Park in January and June 2006. GG rubbing was absent between sisters, as well as between mother-daughter pairs. Maternal females divided their time equally between their sons (28% of total focal observation time) and their sisters (27%). The largest percentages of total grooming time were between the dominant maternal female and the unrelated male (19%) and between the lower ranking mother and her son (17%), suggesting that alliances were strongest between male-female pairs. Adults sons of two of the sisters formed extended sexual relationships with their own aunts (n1=22, n2=16). Sexual interactions also occurred between males (n=8 bouts), father and daughter (n1=6, n2=4) and brother and sister (n1=12). These findings suggest that matrilineal groupings result in reduced sociosexual interaction between females, and that female bonobos may lack behavioral incest avoidance mechanisms for males other than their own sons.

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