Even if they have nothing to lose, chimpanzees opt not to help strangers, according to a team that studied unrelated chimps at two research facilities.
The new findings complement earlier studies indicating that chimps cooperate mainly with close relatives and partners in tit-for-tat exchanges, say Joan B. Silk of the University of California, Los Angeles and her colleagues. Even if chimps, like some monkeys (SN: 9/20/03, p. 181: Unfair Trade: Monkeys demand equitable exchanges), detest getting a lesser reward from experimenters than other chimps do, they show no desire to spread their own wealth with unrelated chimps, the scientists report in the Oct. 27 Nature.
They studied 18 adult chimps, 7 housed together at a Louisiana site and 11 living at a Texas center. Individual chimps first visited testing areas at the two facilities, where they learned to deliver food either to their own tray and that of another animal by, say, pulling a rope, or only to their own tray by, say, pulling a hose.
When put in pairs, individual chimps given the chance to get food showed no special altruistic bent, distributing a goodie to their comrades only about half the time in a series of trials. The same chimps put food in the other tray—which they had no access to—just as often when they were alone.