Data from: Larger brain size indirectly increases vulnerability to extinction in mammals

Although previous studies have addressed the question of why large brains evolved, we have limited understanding of potential beneficial or detrimental effects of enlarged brain size in the face of current threats. Using novel phylogenetic path analysis, we evaluated how brain size directly and indirectly, via its effects on life-history and ecology, influences vulnerability to extinction across 474 mammalian species. We found that larger brains, controlling for body size, indirectly increase vulnerability to extinction by extending the gestation period, increasing weaning age, and limiting litter sizes. However, we found no evidence of direct, beneficial or detrimental, effects of brain size on vulnerability to extinction, even when we explicitly considered the different types of threats that lead to vulnerability. Order-specific analyses revealed qualitatively similar patterns for Carnivora and Artiodactyla. Interestingly, for Primates, we found that larger brain size was directly (and indirectly) associated with increased vulnerability to extinction. Our results indicate that under current conditions the constraints on life-history imposed by large brains outweigh the potential benefits, undermining the resilience of the studied mammals. Contrary to the selective forces that have favoured increased brain size throughout evolutionary history, at present, larger brains have become a burden for mammals.

尽管既往研究已围绕大脑体积演化的动因展开探讨，但我们对当前威胁下脑体积增大可能带来的利弊仍知之甚少。本研究采用新颖的系统发育路径分析（phylogenetic path analysis）方法，针对474种哺乳动物，探究脑体积如何通过影响生活史与生态特征，进而对物种灭绝脆弱性产生直接与间接影响。研究发现，在控制体型变量的前提下，脑体积更大的物种会通过延长妊娠期、推迟断乳年龄以及降低窝仔数，间接提升灭绝脆弱性。然而，即便我们明确纳入了导致脆弱性的各类威胁类型，仍未发现脑体积对灭绝脆弱性存在直接的利弊影响。目级特异性分析显示，食肉目（Carnivora）与偶蹄目（Artiodactyla）呈现出相似的定性结果模式。值得注意的是，针对灵长目（Primates）的分析显示，脑体积更大的物种的灭绝脆弱性提升同时存在直接与间接关联。本研究结果表明，在当前环境下，大脑体积增大对生活史施加的约束，远超其潜在收益，进而削弱了所研究哺乳动物类群的恢复力。与演化史上推动脑体积增大的选择压力相悖，如今更大的脑体积已成为哺乳动物的生存负担。