Monkeys also express affection and make peace with others by grooming each other. Although grooming helps monkeys keep their fur clean of dirt, dead skin, and parasites, it also helps them to build and maintain good social relationships. Grooming seems to be a way to make up after fighting or to make friends with other troop members.
http://www.sandiegozoo.org/animalbytes/t-monkey.html
Male macaque monkeys pay for sex by grooming females, according to a recent study that suggests the primates may treat sex as a commodity.... [Dr. Michael] Gumert found after a male grooms a female, the likelihood that she will engage in sexual activity with the male was about three times more than if the grooming had not occurred.
And as with other commodities, the value of sex is affected by supply and demand factors: A male would spend more time grooming a female if there were fewer females in the vicinity.
"And when the female supply is higher, the male spends less time on grooming ... The mating actually becomes cheaper depending on the market," Gumert said.
http://www.msnbc.msn.com/id/22516331/
