When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants
When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants
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DOI：
10.3389/fevo.2021.742639
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发表时间：
2021-10-22
影响因子：
3
通讯作者：
Fannin, Luke D.
中科院分区：
文献类型：
--
作者：
DeSilva, Jeremy M.;Traniello, James F. A.;Fannin, Luke D.
自从人类最后一次与黑猩猩分享共同祖先以来，人类大脑的大小在600万年内几乎增加了四倍，但自上一次冰河时代结束以来，人类大脑的体积被认为是减少了四倍。这一下降的时间和原因是个谜。在这里，我们使用变点分析来估计人脑进化速度变化的时间。我们发现，人脑在210万年前和150万年前经历了正向变化，这与人类的早期进化和考古记录中明显的技术创新是一致的。但我们也发现，人类大脑的缩小出人意料地是最近的，发生在过去的3000年里。我们的测年结果不支持这样的假设，即大脑尺寸缩小是身体缩小的副产品，是转向农业饮食的结果，也不是自我驯化的结果。我们认为，我们的分析支持这样一种假设，即最近大脑大小的减少可能是由于知识的外化和群体层面决策的优势，部分原因是分布式认知的社会系统以及信息的存储和共享。人类生活在社会群体中，在这个群体中，多个大脑有助于集体智能的出现。虽然很难在人类的深层历史中进行研究，但可以用蚂蚁作为模型来阐明群体规模、社会组织、集体智力和其他潜在的选择性力量对大脑进化的影响。蚂蚁显著的生态多样性和物种丰富性包含了在人类社会性方面的趋同形式，包括大型群体规模、农业生活史、劳动分工和集体认知。蚂蚁提供了广泛的社会系统来生成和测试关于大脑大小扩大或缩小的假说，并帮助解释在人类中发现的大脑进化模式。虽然人类和蚂蚁在社会和认知进化方面代表着非常不同的路线，但蚂蚁提供的洞察力可以广泛地告诉我们影响大脑大小的选择性力量。
Human brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced positive rate changes at 2.1 and 1.5 million years ago, coincident with the early evolution of Homo and technological innovations evident in the archeological record. But we also find that human brain size reduction was surprisingly recent, occurring in the last 3,000 years. Our dating does not support hypotheses concerning brain size reduction as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest our analysis supports the hypothesis that the recent decrease in brain size may instead result from the externalization of knowledge and advantages of group-level decision-making due in part to the advent of social systems of distributed cognition and the storage and sharing of information. Humans live in social groups in which multiple brains contribute to the emergence of collective intelligence. Although difficult to study in the deep history of Homo, the impacts of group size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of labor, and collective cognition. Ants provide a wide range of social systems to generate and test hypotheses concerning brain size enlargement or reduction and aid in interpreting patterns of brain evolution identified in humans. Although humans and ants represent very different routes in social and cognitive evolution, the insights ants offer can broadly inform us of the selective forces that influence brain size.