JohnTheLutheran

Debunking monkey prostitution

So I tweeted a link to this story on how capuchin monkeys “developed prostitution” once human scientists had introduced them to money. This was based on research by Keith Chen (an economist) and Laurie Santos (an evolutionary psychologist).

This has ended up becoming my most retweeted tweet ever. Which is unfortunate, because it seems the research is (to put it politely) questionable.

Rose Dawn posted an extended series of tweets on Sunday dismantling Chen’s and Santos’s claims. Here those tweets are, lightly edited for the purposes of turning into a linear text:

I believe you cannot separate science from the scientists, so let’s have a look at the scientist. Keith Chen is not a primatologist. He is an economist employed by the Cowles Foundation. Chen’s research was substanially funded by a hedge fund, the Whitebox Advisors. Laurie Santos is an evolutionary psychologist, a promoter of just-so stories so loved by right-wing economists.

Capuchin monkeys live in social groups of up to 40 (av. 25) This experimental group was only 7 strong & all unrelated. Chen claimed that capuchins live in a male hierarchy social structure, they do not. it is a female hierarchy based social structure. Chen said his “control” for the social effects of the experiments was to raise the capuchins in captivity (!!!)

Capuchins all have unique faces. They seek faces to look at. Human caregivers are treated as members of the troop. Chen shouldn’t have used human experimenters. Results would have some validity if no humans were present when foodstuffs exchanged for tokens.

Chen claimed he had taught to use money when in reality this was just an extension of tool use coupled with simple counting. What Chen calls “trading” may be just an example of social interaction.

When Chen increased the “price” (number of tokens needed) 1 out of the 3 capuchins in this experiment refused to participate.This capuchin known as AG threw the tokens (money) & food at the experimenter. It was dropped from the study for being “unresponsive”. We do not know what sex AG was or what role it played in the dominance hierarchy of this small social group of capuchins.

AG threw shit at them. Chen said it failed the price test because it is “maximising Cobb-Douglas preferences or is inattentive to prices”. Then did not include the data from capuchin AG in their results. You have to obey the market, even if you are a monkey.

The monkey experimenters then varied the amount of fruit that was given for each token in a predictable manner. One experimenter showed the capuchin 2 pieces of fruit but randomly sometimes only gave 1. Another experimenter showed the capuchin 1 piece of fruit but randomly sometimes gave 2 pieces. Both experiments gave the SAME total pieces. The capuchins chose the experimenter who only displayed 1 piece of fruit but sometimes gave two.

Chen described this preference for a 50% bonus over a 50% loss as an innate “loss aversion” that is also shared by humans when trading.

There is another interpretation of the results. Capuchins are very good at deception and spotting it too. If an experimenter shows two pieces of fruit but only gives one they will be shunned in future interactions.

Capuchins are highly social. A capuchin has been filmed giving hoax predator warning calls, then whilst the others flee, it stashes extra food, now hidden from others.

Capuchins are good tool users.They guard the best tools and fight over them. The tokens (money) used in this experiment could be just tools.

Capuchins live in extended female family groups, males arrive from outside. They have a propensity for violence, so they must learn to trust.

Capuchins do strange things with each other. They’re often seen putting their fingers into eachother’s nose, ears, mouth & touching eyeballs. These potentially dangerous behaviours may be about group bonding: http://www.emory.edu/LIVING_LINKS/vcontact.html. Building trust between troop members. The greatest threat to a capuchin is another capuchin, or rather another troop of capuchins. They frequently make contact with other troops. Troops of capuchins will fight each other violently. Death & severe injury is common. It’s important that capuchins recognise their friends.

Capuchins see human care givers as capuchins. An experimenter offering 2 pieces of fruit yet only giving one will be rejected.

When one capuchin finds a large food source or tool there is great excitement & a propensity for violence. They mediate it with sex. Capuchins have to be violent to protect their troop, but they must avoid intra-troop violence, hence the trust games like eye poking.

In white faced Capuchins, Cebus capucinus, 50% of all sexual mounting is same sex, that is male/male and female/female. The dominant male often displays his erect penis to other males who stroke it. Sex in capuchin troops may reduce stress, facilitate bonding, strengthen friendships & increase group cohesion.