Chimpanzees sometimes smile from pleasure, as when baby chimps play with each other.

当小黑猩猩互相嬉戏时，黑猩猩有时会因为高兴而微笑。

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Since young male chimps were less inclined to play dollies, the authors say their study presents the first evidence of an animal species in the wild in which play differs between males and females.

由于年轻的雄性黑猩猩并不倾向于玩洋娃娃，所以研究者称他们的研究第一次证实了野生动物物种在玩耍方面，雌性和雄性是不同的。

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To find out if chimpanzees share this sense of fairness, Keith Jensen and his colleagues at the Max Planck Institute for Evolutionary Anthropology, in Leipzig, designed a way for chimps to play the ultimatum game.

ECONOMIST: Evolution

The abnormal behaviour declined and the chimps began to play together.

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The chimps are fed a good diet of vegetables, have toys and plenty of space in which to play.

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