German researchers have demonstrated chimpanzees make choices that protect their self-interest more consistently than do humans.

Researchers from the Max Planck Institute of Evolutionary Anthropology in Leipzig studied the chimp's choices by using an economic game with two players. In the game, a human or chimpanzee who receives something of value can offer to share it with another.

If the proposed share is rejected, neither player gets anything.

Humans typically make offers close to 50 percent of the reward. They also reject as unfair offers of significantly less than half of the reward, even though this choice means they get nothing.

The study, however, showed chimpanzees reliably made offers of substantially less than 50 percent, and accepted offers of any size, no matter how small.

The researchers concluded chimpanzees do not show a willingness to make fair offers and reject unfair ones. In this way, they protect their self interest and are unwilling to pay a cost to punish someone they perceive as unfair.

The study appeared in the Oct. 5 issue of the journal Science.