Bonobo societies are unique among the apes. Rather than living in a male dominated world – such as those of chimpanzees, gorillas, and humans – bonobos (Pan paniscus) exist in one where the females hold most of the power. In the communities, despite living in social structures similar to their close cousins the chimpanzees in which the males keep control through fighting and conflict, male bonobos instead derive their status from their mothers. How this has been achieved has long baffled researchers.
A new study suggests that the females may keep control by creating uncertainty as to when they she is ovulating, and thus who fathers her offspring. By maintaining what are known as “sexual swellings”, which usually indicate when a female is at her most receptive and therefore most likely to get pregnant, for a period as long as a month, it makes it almost impossible for a single male to guard her for the entire time. This means that the males have to come up with other tactics to get her to mate, namely spending time socially interacting with and grooming her.
The females were found to display their sexual swellings for up to 31 days, much longer than the period for which they are fertile. Pamela Heidi Douglas/LKBP
“The sexual swellings of female bonobos appear to send mixed messages to males, making it much harder for males to successfully time their mating effort,” explains Pamela Heidi Douglas, who led the research published in BMC Evolutionary Biology. “We found that sometimes females would advertise they were fertile when they were not ovulating and thus unlikely to conceive. During other cycles, females did not display that they were fertile even though they were ovulating.”