Department of Psychology, Franklin and Marshall College, Lancaster, Pennsylvania, USA.
Biological Foundations of Behavior Program, Franklin and Marshall College, Lancaster, Pennsylvania, USA.
Am J Phys Anthropol. 2021 May;175(1):268-281. doi: 10.1002/ajpa.24267. Epub 2021 Mar 13.
The prolonged juvenile period exhibited by primates is an evolutionary conundrum. Here we examine wild chimpanzee feeding development in the context of two hypotheses regarding prolonged development in primates: the needing-to-learn hypothesis and the expensive brain hypothesis.
We studied wild chimpanzee (Pan troglodytes schweinfurthii) offspring at Gombe National Park, Tanzania. We analyzed 41 years of observational behavioral data collected between 1975 and 2016 from 81 offspring. We characterized feeding development in the first 10 years of life via four different measures: (1) proportion of observation time spent feeding; (2) diet composition; (3) diet breadth; and (4) diet maturity as measured by similarity to maternal diet. We used mixed effects models to examine changes with age and by sex, while controlling for season.
Feeding time, diet breadth, and diet maturity exhibited the most substantial increases with age in the first 6 years, with no significant change thereafter. Males and females showed different patterns of change in diet breadth by age, but did not differ by age 10. Diet composition did not change significantly with age and did not differ by sex.
We found that chimpanzee offspring attained adult-like feeding behaviors between 4 and 6 years of age, concomitant with the completion of weaning. Thus, our data do not support the needing-to-learn feeding skills hypothesis of a prolonged juvenile period, but additional data are needed to evaluate how and when adolescent chimpanzees are able to make foraging decisions independent of their mothers. Existing data on growth provides support for the expensive brain hypothesis, however, these hypotheses are not necessarily mutually exclusive. As more studies across taxa accumulate sufficient datasets on a range of developmental metrics, we will be able to achieve a more robust understanding of prolonged development in primates.
灵长类动物表现出的漫长幼体期是一个进化难题。在这里，我们在两个关于灵长类动物发育延长的假说的背景下检查野生黑猩猩的喂养发育：需要学习假说和昂贵大脑假说。
我们在坦桑尼亚的贡贝国家公园研究了野生黑猩猩（Pan troglodytes schweinfurthii）的后代。我们分析了 1975 年至 2016 年间从 81 只后代收集的 41 年观测行为数据。我们通过以下四种不同的措施来描述生命前 10 年的喂养发育：（1）观察时间中用于喂养的比例；（2）饮食组成；（3）饮食广度；（4）饮食成熟度，用与母系饮食的相似性来衡量。我们使用混合效应模型来检查年龄和性别随年龄的变化，同时控制季节因素。
在生命的前 6 年中，喂养时间、饮食广度和饮食成熟度随年龄增长而显著增加，此后没有显著变化。雄性和雌性在年龄的饮食广度变化模式不同，但在 10 岁时没有差异。饮食组成随年龄没有显著变化，也不因性别而异。
我们发现，黑猩猩后代在 4 到 6 岁之间就获得了类似成年的喂养行为，同时也完成了断奶。因此，我们的数据不支持需要学习喂养技能的漫长幼体期假说，但需要更多的数据来评估青少年黑猩猩何时以及如何能够独立于其母亲做出觅食决策。现有的关于生长的资料支持昂贵大脑假说，然而，这些假说不一定相互排斥。随着更多的跨类群研究积累足够的关于一系列发育指标的数据集，我们将能够更深入地了解灵长类动物的延长发育。
