Spontaneous Altruism by Chimpanzees and Young Children

People often act on behalf of others. They do so without immediate personal gain, at cost to themselves, and even toward unfamiliar individuals. Many researchers have claimed that such altruism emanates from a species-unique psychology not found in humans' closest living evolutionary relatives, such as the chimpanzee. In favor of this view, the few experimental studies on altruism in chimpanzees have produced mostly negative results. In contrast, we report experimental evidence that chimpanzees perform basic forms of helping in the absence of rewards spontaneously and repeatedly toward humans and conspecifics. In two comparative studies, semi�Cfree ranging chimpanzees helped an unfamiliar human to the same degree as did human infants, irrespective of being rewarded (experiment 1) or whether the helping was costly (experiment 2). In a third study, chimpanzees helped an unrelated conspecific gain access to food in a novel situation that required subjects to use a newly acquired skill on behalf of another individual. These results indicate that chimpanzees share crucial aspects of altruism with humans, suggesting that the roots of human altruism may go deeper than previous experimental evidence suggested.

人类常为他人行事，此类行为不求即时个人回报，且需自身付出代价，甚至施助于陌生个体。诸多研究者认为，此类利他行为源自人类独有的心理机制，而在与人类现存亲缘关系最近的进化近亲（如黑猩猩）身上并未发现该机制。为支持这一观点，现有少量针对黑猩猩利他行为的实验研究大多得出了否定性结果。与之相反，本研究报告的实验证据表明，黑猩猩会自发且反复地向人类及同种个体提供基础形式的帮助，且无需任何奖励。在两项对照研究中，半自由放养的黑猩猩对陌生人类的帮助程度与人类婴儿相当，且该行为不受是否存在奖励（实验1）或帮助是否需付出代价（实验2）的影响。在第三项研究中，黑猩猩会在全新情境下帮助无亲缘关系的同种个体获取食物，该情境要求实验对象为了他人而运用新习得的技能。上述结果表明，黑猩猩与人类共享利他行为的关键特征，这意味着人类利他主义的演化根源或许比此前实验证据所暗示的更为深远。