I don't know if it's true that Wild chimpanzees exchange meat for sex but I know some vegetarians who may find it interesting.
Wild female chimpanzees copulate more frequently with males who share meat with them over long periods of time, according to a study led by researchers from the Max Planck Institute for Evolutionary Anthropology in Germany, published in the open-access, peer-reviewed journal PLoS ONE April 8.It probably works for humans as well.
I'm going out to buy some steaks for dinner.
The original paper is Gomes and Boesch (2009)
Gomes, C.M. and Boesch, C. (2009) Wild Chimpanzees Exchange Meat for Sex on a Long-Term Basis. PLoS ONE 4(4): e5116. DOI:10.1371/journal.pone.0005116