Abstract Friendship naturally leads to treating some people differently from the way we treat everyone else. One manifestation of such preferential treatment is in the domain of prosociality: we are more likely to extend favors towards our friends. Little is known about the developmental and evolutionary roots of such preferential prosociality. Here, we investigate whether young children and chimpanzees show partiality towards friends in helping contexts. Results show that young children at the age of three – when they first form preferential peer relationships – already bias their helping decisions in favor of their friends, both when they have to make a choice whether to help a friend or a neutral peer (Study 1) and when measuring their overall motivation to help (Study 2). In Study 3, by combining observational and experimental methods, we demonstrate similar though less robust motivations to provide help preferentially to friends in our closest living relatives, chimpanzees. Taken together, these studies suggest that partiality towards friends is grounded early in ontogeny and human evolution.

中文翻译：

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帮助幼儿和黑猩猩表现出对朋友的偏爱

摘要 友谊自然会导致对待某些人的方式与我们对待其他人的方式不同。这种优惠待遇的一种表现是在亲社会领域：我们更有可能向我们的朋友伸出援手。人们对这种优先亲社会性的发展和进化根源知之甚少。在这里，我们调查幼儿和黑猩猩是否在帮助环境中对朋友表现出偏袒。结果表明，三岁的幼儿——当他们第一次建立优先同伴关系时——已经使他们的帮助决定偏向于有利于他们的朋友，无论是在他们必须做出选择是帮助朋友还是中立的同伴时（研究 1 ) 以及衡量他们提供帮助的整体动机时（研究 2）。在研究 3 中，通过结合观察和实验方法，我们表现​​出类似但不那么强烈的动机，优先向我们最亲近的亲戚黑猩猩的朋友提供帮助。综上所述，这些研究表明，偏爱朋友的根源在于个体发育和人类进化的早期。