School of Biology, University of St Andrews, St Andrews, UK.
Nature. 2018 May;557(7706):554-557. doi: 10.1038/s41586-018-0127-x. Epub 2018 May 23.
The human brain is unusually large. It has tripled in size from Australopithecines to modern humans and has become almost six times larger than expected for a placental mammal of human size . Brains incur high metabolic costs and accordingly a long-standing question is why the large human brain has evolved . The leading hypotheses propose benefits of improved cognition for overcoming ecological, social or cultural challenges. However, these hypotheses are typically assessed using correlative analyses, and establishing causes for brain-size evolution remains difficult. Here we introduce a metabolic approach that enables causal assessment of social hypotheses for brain-size evolution. Our approach yields quantitative predictions for brain and body size from formalized social hypotheses given empirical estimates of the metabolic costs of the brain. Our model predicts the evolution of adult Homo sapiens-sized brains and bodies when individuals face a combination of 60% ecological, 30% cooperative and 10% between-group competitive challenges, and suggests that between-individual competition has been unimportant for driving human brain-size evolution. Moreover, our model indicates that brain expansion in Homo was driven by ecological rather than social challenges, and was perhaps strongly promoted by culture. Our metabolic approach thus enables causal assessments that refine, refute and unify hypotheses of brain-size evolution.
人类大脑异常庞大。从南方古猿到现代人类，它的体积增加了两倍，与人类大小的胎盘哺乳动物相比，大脑的体积几乎增加了六倍。大脑需要消耗大量的代谢能量，因此长期以来人们一直想知道，为什么人类的大脑会进化得如此之大。主流假说提出，改善认知能力有助于人类克服生态、社会或文化方面的挑战。然而，这些假说通常是通过相关分析来评估的，因此要确定大脑大小进化的原因仍然很困难。在这里，我们引入了一种代谢方法，使我们能够从大脑代谢成本的经验估计出发，对大脑大小进化的社会假说进行因果评估。我们的方法基于形式化的社会假说，对大脑和身体的大小进行了定量预测。我们的模型预测，当个体面临 60%的生态挑战、30%的合作挑战和 10%的群体间竞争挑战时，智人大小的大脑和身体就会进化，这表明个体间的竞争对驱动人类大脑大小的进化并不重要。此外，我们的模型还表明，人类大脑的扩张是由生态挑战而不是社会挑战驱动的，也许是受到了文化的强烈推动。因此，我们的代谢方法能够进行因果评估，从而完善、反驳和统一大脑大小进化的假说。
