Dossiers Sexologiques special: Prostitution in animals

31 January 2008

We call it the oldest profession; it now appears it might even be older than we think-older than our evolutionary split from the monkeys!

A recent research published in the journal Animal Behaviour reports on monkeys paying for sex. That’s right, monkeys paying for sex. Longtailed macaque males use grooming to pay for sexual access to females. Just as in human markets, the more limited the commodity (here number of sexually receptive females available) the higher the prices. When there are many females present males pay less to buy sex, when there are a few, males pay more. The preferred payment method is grooming. The price equals the length of grooming bout before sex is provided: the longer the grooming bout, the higher the price. The availability of sexual partners (relative abundance of the resource) is not the only biological market force that determines the price in this trade of social commodities. The quality of the sexual partner (value of the resource) also determines the price. Higher quality females, usually higher ranking ones, set their price higher: males need to groom them longer if they want to buy sex from them.

So basically, what seems to be happening here is that females do not just go around offering sex to any odd male that might be passing by. Males have to put a lot of effort into foreplay in order to get sex. Sounds familiar enough: isn’t this what happens in human couples? One doesn’t just jump straight into bed with someone else; there’s the first base, the second base, the third base and only then, if one is able to get that far, does the home run occur. One might conclude monkeys are not all that different from us when it comes to sex. What’s in it for females though? Well, the assumption is they are forming alliances with males by getting groomed. This may then provide them with more stable environment for their offspring and protection from the males they formed alliances with. There’s also the immediate pleasure of being groomed. The act of grooming has beneficial physiological effects such as stress relief and increase in tolerance and cooperation. This may “make the male more at ease to attempt a sexual act and the female more tolerant of his sexual advances”Dr Gumert reports in Animal Behaviour.

Now, this scenario may occur in Longtailed macaques and humans alike, but another, less pleasant chain of effects also occurs in both species. In the macaques, males sometimes assume an alternative mating strategy of ‘consortship’ where they monopolize the female. Such males fight with other males for their self-proclaimed rights to female’s body and force the female into sexual activities. Not very cultured…

Another support for the notion that prostitution occurs in nature comes from report of prostitution in Adelaide penguins, published in 1998 in journal The Auk. Females exchanged sex for nest material: small pebbles. They use these pebbles to build nests on which they lay eggs. Since pebbles are in high demand during nesting season, stealing and prostitution are commonly used to acquire these worthy objects. The more pebbles the better for penguins, because come spring, with melted snow arrive the floods and only the biggest nests survive. Otherwise monogamous, these penguin females approach, seduce and copulate with other unmated males while their unsuspecting partner stays at the nest. Females come back to their customers up to ten times, taking a pebble each time. The valued pebbles are otherwise rigorously defended by the males against other penguins, but not when sex is used to pay for the precious stones. In fact, some males were so vain that they let females take pebbles even after only flirting with them. One male was observed losing 62 pebbles in an hour this way!

What such males may gain is paternity over female’s offspring, offspring that they do not have to invest in any further. It is still unclear exactly what the females are after in this extraordinary behaviour: are the pebbles or the sex with another male more important resource for females? Pebbles are important for nest survival, but sperm from other males may affect the paternity of their offspring. Maybe, they choose to have sex with other, better quality males and only pick up the pebbles to fool their long-term partners, effectively signalling to them “I was just out collecting some pebbles darling, no funny business, honestly.” Future research may determine if the pebbles are these ladies’ payment or alibi.