"We believe the males may be using crop-raids as a way to advertise their prowess to other group-members, especially the opposite sex. Such daring behaviour certainly seems to be an attractive trait and possessing a sought-after food item, such as papaya, appears to draw even more positive attention from the females," said Dr Kimberley Hockings from the University of Stirling's Department of Psychology, the lead researcher.
The study was carried out in the West African village of Bossou in the Republic of Guinea. According to the researchers, it is the only recorded example of sharing of plant food by unrelated, non-provisioned wild chimpanzees.
"It is unusual behaviour as even though the major part of chimpanzees' diets consists of plant foods, wild plant food sharing (defined as an individual holding a food item but allowing another individual to consume part of that item) occurs infrequently. However, in chimpanzee communities that engage in hunting, meat is frequently used as a 'social tool' for nurturing alliances and social bonds," said Dr. Hockings.
"This research shows that chimpanzees at Bossou use crop-raiding as an opportunity to obtain and share desirable foods, providing further insights into the evolutionary basis of human food sharing. In humans, the pursuit of certain foods is also strongly sex-biased; for example, it has been proposed that men in hunter-gatherer societies acquire large and risky-to-obtain food packages for social strategising and to garner attention," the researcher added.
The study showed that adult males mainly shared the spoils of their crop-raids with females of reproductive age, particularly with a female within the group who took part in most consortships.
"The male who shared the most food with this female engaged in more consortships with her and received more grooming from her than the other males, even the alpha male. Therefore the male chimpanzees appear to be 'showing off' and trading their forbidden fruit for other currencies, i.e. 'food-for-sex and -grooming'," Dr. Hockings said.
The study has been published in open-access journal PLoS One.