The oldest profession: older then we thought

Last week’s film about sex and evolution raised questions about the similarities and differences between money, ape, and human sexuality. The issue has been in the news of late, too. According to news reports, a recent study suggests that male macaques pay for sex with grooming:

Selling sex is said to be humankind’s oldest profession but it may have deep evolutionary roots, according to a study into our primate cousins which found that male macaques pay for intercourse by using grooming as a currency.

Michael Gumert of Nanyang Technological University in Singapore made the discovery in a 20-month investigation into 50 long-tailed macaques in Kalimantan Tengah, Indonesia, New Scientist reports on Saturday.

On average, females had sex 1.5 times per hour.

But this rate jumped to 3.5 times per hour immediately after the female had been groomed by a male — and her partner of choice was likely to be the hunky monkey that did the grooming.

The report also suggests that the cost of obtaining sex varied with supply and demand. If females were abundant, males could woo a potential mate with just eight minutes of grooming. But if no other females were in the area, the male would have to spend twice as long grooming.

This example highlights one of the points of last week’s film—the importance of competition for mates in the evolutionary process. For more, see excerpts of the film on sexual selection in peacocks, polyandry in jacanas, and sex and social organization among chimps and bonobos.