Money for monkeys
This week's paper is "Do capuchin monkeys (Cebus apella) use tokens as symbols?" by E. Addessi and coauthors, published in Proceedings of the Royal Society.
Humans use symbols in various ways, from drawings that somewhat resemble the object represented to national flags and religious symbols that represent complex ideologies (or at least group identity). Is symbolic reasoning a uniquely human trait, at least on this planet?
Chimps have been shown to use symbols, correctly choosing between previously learned symbols for "food" and "tool" when presented with a new tool or food item, while another chimp learned numbers well enough to pick the higher one when that resulted in more food. But what about monkeys?
The authors trained capuchin monkeys to exchange tokens (poker chips, metal nuts, etc.) for food. "Denominations" were assigned to each of two tokens so that one could be exchanged for 3 times as much food as the other. After the monkeys had some opportunity to learn the exchange-value of each token, through repeated exchange sessions, they were given opportunities to choose between one 3-treat token B versus 1 to 5 1-treat tokens A. A smart monkey would pick one B token over 2 A tokens but not over 4 A tokens.
Actual performance varied among monkeys. Four of ten followed the optimum strategy. Four monkeys learned to prefer the high-value token B, but apparently didn't count how many low-value token A's were available as an alternate choice.
Only one monkey consistently chose correctly between several B versus several A tokens. The question is, could that monkey find a girlfriend?
In other words, to what selective forces, operating on our ancestors, can we attribute the ability of some of us to compose music or prove mathematical theorems?
Also this week: