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http://www.newscientist.com/article/dn17394-monkey-stock-market-prone-to-fluctuations-too.html

Monkey 'stock market' prone to fluctuations too 

10:06 30 June 2009 by Colin Barras 

Monkeys might not deal in stocks and shares, but they do trade commodities, 
and now it seems that monkey exchange rates are influenced by supply and 
demand.

Grooming acts as a common currency among non-human primates, says Ronald Noë 
at the University of Strasbourg, France. It is exchanged for food, greater 
tolerance from dominant members of the group – and even for sex.

To see how the exchange system works, Noë's team created an artificial market 
in groups of vervet monkeys by introducing a plastic box filled with food 
that only one subordinate female was trained to open.

An hour after the female opened the box, the biologists noted that she was 
rewarded by being groomed more often and for longer by other group members, 
and that she could afford to groom dominant group members less often.

Next, the team halved the importance of the female's ability to provide food, 
by introducing a second lunch box that only a second female could open. The 
first female's grooming "stock value" decreased, while the second monkey's 
rose, until both arrived at roughly the same value and were groomed for the 
same amount of time.

"One can say that the second provider was groomed at a cost of the first 
provider," says Noë.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 
10.1073/pnas.0812280106)