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. 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
