Ugly Monkey's foreplay lasts longer

Male macaques exchange grooming for the right to mate with females whose fur they have cleaned, a study has found.The researchm by Michael Gumert, of the Division of Psychology at Nanyang Technological University in Singapore, and colleagues, has been accepted for publication in the journal Animal Behaviour.
"I found that the amount of grooming a male performs on a female during a sexual interaction is related to the supply/demand ratio of females per male around the male-female pair at the time of the grooming," says Gumert.
Put another way, male monkeys - especially lower status ones - have to groom more to get more action when fewer females are around.The activity often sexually excites the monkeys, particularly the males, so many scientists suspect it evolved into foreplay in humans.(more on monkey sex)