Premasticated food transfer, when an individual partially breaks down food through chewing and feeds it to another individual, usually mouth-to-mouth, is described widely across human cultures. This behavior plays an important role in modern humans' strategy of complementary feeding, which involves supplementing maternal milk in infant diets with processed, easily digestible versions of adult foods. The extent to which other primates engage in premasticated food transfer with infants is unclear, as premasticated food transfers have been only occasionally reported in other ape species. We investigated premasticated food transfers in 62 mother-infant pairs of wild chimpanzees at Ngogo, Uganda, as well as unresisted food taking, when mothers passively allow infants to seize food. We evaluated the presence or absence and rates of premasticated food transfer and unresisted food taking relative to maternal parity and infant age and sex and assessed the food species and part used. We found that chimpanzee mothers regularly shared premasticated food with their infants aged between 6 months and 4 years, but they were more likely to share, and more frequently shared, with younger infants. The frequency with which females shared premasticated food may relate to maternal experience, as multiparous females shared premasticated food more often than did first-time mothers, which we did not find with unresisted food taking. Both easy-to-chew, commonly eaten foods and tougher, rarely eaten foods were shared. Premasticated food transfer and unresisted food taking may be infant-rearing strategies to facilitate the transition from a diet of exclusive maternal milk to solid food during early infancy. Premasticated food transfer in particular may provide energetic, immune, or growth benefits to infants through reduced chewing effort and maternal saliva. Given our findings in chimpanzees and earlier reports in other ape species, we suggest that the foundation of complementary feeding, a uniquely hominin strategy, might have been present in a common ancestor shared with the other great apes in the form of premasticated, mouth-to-mouth food transfer by mothers with their offspring.

中文翻译：

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野生黑猩猩母亲及其婴儿的过早熟食物转移：产妇对产，婴儿年龄和性别以及食物特性的影响。

当一个人通过咀嚼将食物分解成一部分并将其喂给另一个人（通常是口对口）时，过早咀嚼食物的转移在整个人类文化中得到了广泛描述。这种行为在现代人的补充喂养策略中起着重要作用，该策略涉及以加工，易消化的成人食品形式补充婴儿饮食中的母乳。尚不清楚其他灵长类动物与婴儿进行过咀嚼食物转移的程度，因为在其他猿类中仅偶尔报道过咀嚼食物转移。我们调查了乌干达恩哥戈（Ngogo）的62对母婴野生黑猩猩的过早摄入食物的转移，以及当母亲被动地允许婴儿抓住食物时未抵抗的食物摄取。我们评估了母体平价，婴儿年龄和性别相对而言，过早摄入食物和不抵抗食物摄入的存在与否和发生率，并评估了所使用的食物种类和部分。我们发现，黑猩猩的母亲经常与年龄在6个月至4岁之间的婴儿分享食用过咀嚼的食物，但黑猩猩的母亲更容易与年龄较小的婴儿分享食物，而且分享频率更高。女性分享过咀嚼食物的频率可能与孕产妇的经历有关，因为与初次母亲相比，不同性别的女性分享过咀嚼食物的频率更高，这在我们坚持不吃食物的情况下并没有发现。容易咀嚼，通常食用的食物和较硬，很少食用的食物都被共享。过早的食物转移和不加选择的食物摄取可能是育婴策略，以促进婴儿期早期从纯母乳饮食向固体食物的过渡。特别地，过早咀嚼食物的转移可能会通过减少咀嚼力度和减少产妇唾液而为婴儿提供能量，免疫或生长方面的好处。鉴于我们在黑猩猩中的发现以及在其他猿类中的早期报道，我们建议，与其他大猩猩共享的共同祖先可能以过早咀嚼，嘴巴到嘴的形式存在补充喂养的基础，这是一种独特的人参战略。母亲及其后代的口粮转移。通过减少咀嚼力度和产妇唾液，对婴儿的成长或生长有益。鉴于我们在黑猩猩中的发现以及在其他猿类中的早期报道，我们建议，与其他大猩猩共享的共同祖先可能以过早咀嚼，嘴巴到嘴的形式存在补充喂养的基础，这是一种独特的人参战略。母亲及其后代的口粮转移。通过减少咀嚼力度和产妇唾液，对婴儿的成长或生长有益。鉴于我们在黑猩猩中的发现以及在其他猿类物种中的早期报道，我们建议，与其他大猿类共有的共同祖先，可能以过早熟化，嘴巴到嘴的形式出现了补充喂养的基础，这是一种独特的人参战略。母亲及其后代的口粮转移。