True altruism seen in chimpanzees, giving clues to evolution of human cooperation

True altruism seen in chimpanzees, giving clues to evolution of human cooperation
A pair of studies suggests the evolutionary roots of humanlike cooperation can be seen in chimpanzees, albeit in rudimentary forms.


Both studies provide powerful evidence for forms of cooperation in our closest relatives that have been difficult to demonstrate in other animals besides humans, says Brian Hare, an evolutionary anthropologist at Duke University in Durham, North Carolina, who was not involved with the research.

In the first study, psychologists Martin Schmelz and Sebastian Grneisen at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, trained six chimps at the Leipzig Zoo to play a sharing game. Each chimp was paired with a partner who was given a choice of four ropes to pull, each with a different outcome: give just herself a banana pellet; give just the subject a pellet; give both of them pellets; or forgo her turn and let her partner make the decision instead.

Unbeknownst to these partner chimpanzees, the chimp that always started the gamea female named Taiwas trained to always choose the last option, giving up her turn. From the partners point of view, this was a risky choice, Grneisen says, as Tai risked losing out entirely on the banana pellets. Over dozens of trials, after Tai gave up her turn, the six partners pulled the rope that rewarded both themselves and Tai with a treat 75% of the time, indicating they valued her risking her own treats to help them.

But the researchers also wanted to see whether the subjects were willing to give up some of their own reward to repay Tai for her perceived kindness. That kind of reciprocity is often claimed to be a landmark of human cooperation, and we wanted to see how far we could push it with the chimps, Grneisen says.

The team repeated the experiment, except this time when Tai passed the turn to the subjects, the subjects had the option of either giving themselves four banana pellets and Tai none, or giving both themselves and Tai only three banana pellets. The subjects chose the sacrifice option 44% of the time, compared with 17% of the time when the experimenters, not Tai, made the initial decision. This suggests that the chimps frequently felt compelled to reward Tai for her perceived unselfishness , even at their own expense, the researchers report today in the
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