Chimpanzees try to catch a matza thrown towards them at the Ramat Gan Safari, near Tel Aviv April 7, 2009. REUTERS/Amir Cohen

WASHINGTON (Reuters) - Human females may get offended at dates who expect a little something extra after they buy a steak dinner, but for chimpanzees, the exchange may be a fair one, German researchers reported on Tuesday.

They found that female chimpanzees mate more frequently with males who often share meat with them.

“Our results strongly suggest that wild chimpanzees exchange meat for sex, and do so on a long-term basis,” Cristina Gomes of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany said in a statement.

“Males who shared meat with females doubled their mating success, whereas females, who had difficulty obtaining meat on their own, increased their caloric intake without suffering the energetic costs and potential risk of injury related to hunting.”

Writing in the Public Library of Science journal PLoS ONE, Gomes and colleague Christophe Boesch said they watched chimps living in the Tai National Park in Ivory Coast.

"The meat for-sex hypothesis is a plausible explanation for male-female meat sharing in this species, as chimpanzees are highly promiscuous, they have a certain degree of female choice and hunters can usually control the sharing of their catch," they wrote in their report, published onlinehere.

Males were more likely to share meat with females whose bodies showed they were in a fertile period, but even excluding these couplings, it was clear that mating behavior occurred more often between males and the females they were regularly sharing meat with.

“Our findings add to the ever-growing evidence suggesting that chimpanzees can think in the past and the future and that this influences their present behavior,” Boesch said.

“These findings are bound to have an impact on our current knowledge about relationships between men and women; and similar studies will determine if the direct nutritional benefits that women receive from hunters in human hunter-gatherer societies could also be driving the relationship between reproductive success and good hunting skills,” Gomes added.