Female Solicitation and Male Rejection During Mating Events in Wild Chimpanzees

Humans are seemingly unique among the great apes with regard to their monogamous mating behavior. Since chimpanzees (Pan troglodytes) are humans closest living relative, understanding their actions may give insight into the evolutionary development of certain behaviors. In this paper, the mating behavior of chimpanzees will be evaluated in hopes of better understanding any similarities or differences compared to that of humans. Wild male chimpanzees have shown to reject solicitations from females at full swelling. The hypothesis being tested was that a male chimpanzee will reject a female who solicits a mating event due to age, rank, and parity. Long term data from Gombe National Park in Tanzania, Africa was used to test this. As expected, parous females were less likely to be rejected than nulliparous females, rejection was more likely if several other swollen females were present, and rejection was less likely if the female was higher-ranking/older. Surprisingly, it was found that younger males were more likely to reject females than prime males were. This was most likely due to the fact that almost always, higher-ranking males were also present, which may have deterred young males from mating. The results also showed that there was no effect of male rank and female reproductive state on the probability of rejection. The findings of this study may help to show a potential evolutionary step towards conscious mate selection as seen in humans.