London, October 29 : Chimpanzees very closely observe who all are grooming them, and ultimately return favours to them while freezing out others, according to a new study.
Cristina Gomes, a behavioural ecologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, came up with this finding after observing wild chimpanzees living in Tai National Park in Cote D'Ivoire for about 3000 hours.
She says that grooming, in a way, works like currency in chimpanzees.
"If you don't have a set price, then you're susceptible to being cheated and cooperation would probably break down," New Scientist magazine quoted her as saying.
She revealed that among chimps, grooming seemed to be a hygienic practice to pluck parasites off fur, as well as a social glue between related and unrelated apes.
For her study, Gomes spent several years recording the daily behaviour of 44 chimps. Each day, she tracked an individual chimpanzee, recording whom it groomed, who groomed it, and the length of each session on a handheld computer.
The researcher finally accrued 87 hours of grooming.
While the animals were found to forgo a "you scratch my back, I'll scratch yours approach" on a day-to-day basis and many debts remained unsettled, the researchers did observe that a tit-for-tat payback system emerged about a week later.
"Most of their reciprocity is going on over a longer period of time," Gomes said.
She further said that hormones were a likelier explanation for the behaviour of chimpanzees, and that the same could apply to humans.
According to her, primates could be made to learn to associate generosity with some animals and meanness with others by finely tweaking the levels of endorphins.
"I think that this is the basis of human friendships," she said.
A research article on the study has been published by the journal Proceedings of the Royal Society B.