Institute of Psychology, University of São Paulo, São Paulo, Brazil.
School of Arts, Sciences and Humanities, University of São Paulo, São Paulo, Brazil.
Am J Primatol. 2021 May;83(5):e23251. doi: 10.1002/ajp.23251. Epub 2021 Mar 5.
Tufted capuchin monkeys (Sapajus spp.) are the only Neotropical Primates that regularly use tools in the wild, but only one population of bearded capuchin monkeys (Sapajus libidinosus) is known to habitually use sticks as probes. In this population, males are typically the only sex to use stick tools, something unexpected, since there are no obvious physical constraints, and females do use stone tools in the wild and sticks in experimental conditions. We investigated the development of probe tool use in eight infants to clarify whether social influences on learning varied between the sexes, as tool use learning by capuchin monkeys is a socially biased process. We found that in the first 10 months of age, females manipulate sticks as much as males, but after 10-12 months of age, males begin to manipulate them at higher frequencies. We examined if social connections-as opportunities for social learning-could explain this difference and verified that, on close distance social networks, infant males and females have similar connections with older males. However, males observe probe tool use events more often than females when close to such events. The higher frequency of manipulation of sticks, as well as the higher rates of probe tool use observation, appear to be the key to understand why only males are probe tool users in this population. Since there are only male potential models of probe use, a sex motivational bias could explain the sex difference in observation; a bias in observation could explain the differences in manipulation-and manipulation rates would certainly influence the chances of individual, trial-and-error learning (a case of "local/stimulus enhancement").
卷尾猴（Sapajus spp.）是唯一一种在野外经常使用工具的新热带灵长类动物，但已知只有一个髯猴种群（Sapajus libidinosus）习惯性地使用树枝作为探针。在这个种群中，只有雄性通常会使用树枝工具，这是出乎意料的，因为没有明显的身体限制，而且雌性在野外会使用石器，在实验条件下也会使用树枝。我们研究了 8 只幼猴探针工具使用的发展情况，以明确性别之间的社会影响是否存在差异，因为卷尾猴的工具使用学习是一个具有社会偏见的过程。我们发现，在 10 个月大之前，雌性和雄性一样经常摆弄树枝，但在 10-12 个月大之后，雄性开始更频繁地摆弄树枝。我们研究了社会联系（即社会学习的机会）是否可以解释这种差异，并证实，在近距离的社会网络中，幼猴雄性和雌性与年长雄性的联系相似。然而，当靠近这些事件时，雄性观察探针工具使用事件的频率比雌性更高。更频繁地摆弄树枝，以及更高的探针工具使用观察率，似乎是理解为什么只有雄性是该种群探针工具使用者的关键。由于只有雄性是潜在的探针使用者模型，性别动机偏见可能可以解释观察到的性别差异；观察到的偏见可能可以解释操作的差异，而操作的频率肯定会影响个人、试错学习的机会（即“局部/刺激增强”的情况）。
