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Monkeynomics

February 7, 2011

Eva Gusnowski

Ah, the law of supply and demand. Economics has always been a subject that has thwarted me, and I could never quite get a handle on it. Yet this one law was one that I always thought that I could understand. Higher supply levels means a lower price; low supply levels means a higher price. It all seemed so straightforward. And then I got into science and thought that I had left it all behind. Little did I know that science has a law of supply and demand all its own, called the biological market.

Animal economics is a difficult thing to study. There are no verbal negotiations or contracts; so only the trading of goods and services can be analyzed. In primates, one service, grooming, is exchanged as a sort of currency. Grooming is altered in quantity and quality depending on the laws of supply and demand, and is exchanged for other goods or services. The grooming currency is exchanged for tolerance at food sites, access to newborns, support in conflicts as well as the compliance of females during mating season.

 

          Eva Gusnowski, monkeynomics, supply and demand

 

So how is the “grooming currency rate” changed in different monkey markets? Let’s take a look at a few examples.

1) It's the Monopoly guy!
Food was provided to either one vervet monkey (monopoly) or two vervet monkeys (duopoly) to give to the other members of the group. When there was a monopoly, the single food provider received high levels of grooming (based on time). However, when a second food provider was introduced, the amount of grooming time given to provider #1 was reduced.

2) Be my baby
Female primates are often attracted to infants in their group, even when they are not the biological mothers. However, they seem to have to pay the mother (in grooming time, of course) in order to increase their chances of handling the infant. A study in 2007 found that in long-tailed macaques, the amount of time a female had to spend grooming the mother increased when the supply of infants was low. When the number of infants in the group increased, the grooming payment correspondingly decreased.

3) Sexy time
Male-to-female grooming in long-tailed macaques tended to occur only when females were sexually active. These male-to-female grooming sessions also tended to increase in length when the females were higher ranking, mating was involved, or the female presented its hindquarters to the male. Additionally, an increase in female sexual activity was found when these grooming sessions occurred. However, when more sexually active females were present, the amount of time a male spent grooming a female decreased.

4) Who’s the boss?
It’s not Charles, it’s the high ranking females. Apparently you are worth more when you’re the CEO of the monkey group. Although female primates offer grooming to other females in reciprocation, grooming also follows a bottom-up pattern. Low-ranking females will groom high-ranking females more often in order to gain agonistic support and other rank-related benefits.

 

        Eva Gusnowski, monkeynomics, supply and demand



So there you have it. Economics; so simple that a monkey can understand it. Except for me. I still don’t really get it, even though I’ve just had it explained to me by a monkey.

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