It turns out that one of humanity's oldest professions may be even older than we thought: In a recent study of macaque monkeys in Indonesia, researchers found that male primates "paid" for sexual access to females — and that the going rate for such access dwindled as the number of available females went up.
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According to the paper, "Payment for Sex in a Macaque Mating Market," published in the December issue of Animal Behavior, males in a group of about 50 long-tailed macaques in Kalimantan Tengah, Indonesia, traded grooming services for sex with females; researchers, who studied the monkeys for some 20 months, found that males offered their payment up-front, as a kind of pre-sex ritual. It worked. After the females were groomed by male partners, female sexual activity more than doubled, from an average of 1.5 times an hour to 3.5 times. The study also showed that the number of minutes that males spent grooming hinged on the number of females available at the time: The better a male's odds of getting lucky, the less nit-picking time the females received. Though primates have been observed trading grooming for food sharing or infant care, this is the first time this kind of exchange has been observed between male and female primates in a sexual context, says lead researcher Michael Gumert of Singapore's Nanyang Technological University, demonstrating that the amount of time a male macaque "will invest in [its] partner" depends largely on how many options it has around.
