The allometry of brain size in mammals

Why some animals have big brains and others do not has intrigued scholars for millennia. Yet, the taxonomic scope of brain size research is limited to a few mammal lineages. Here, we present a brain size dataset compiled from the literature for 1,552 species with representation from 28 extant taxonomic orders. The brain–body size allometry across all mammals is (Brain) = −1.26 (Body)^0.75. This relationship shows strong phylogenetic signal. Thus, we conducted additional allometries using median species values for each order, family, and genus to ensure evolutionary independence. Slopes from these analyses at different taxonomic levels all approximate ~0.75 scaling. Why brain size scales to the 3/4 power to body size across mammals is to our knowledge unknown. Slopes within taxonomic orders, exhibiting smaller size ranges, are generally shallower than 0.75 and range from 0.24 to 0.81 with a median slope of 0.64. Published data on brain size are lacking for the majority of extant mammals ...数千年来，为何部分动物拥有较大脑容量而其余动物没有，这一问题一直令学界学者着迷。然而，当前脑容量研究的分类学范畴仅局限于少数哺乳动物支系。本研究构建了一份基于文献汇编的脑容量数据集，涵盖28个现存分类目、共计1552个物种。所有哺乳动物的脑-身体大小异速生长（allometry）关系为：脑容量 = −1.26 × 身体质量^0.75，该关系表现出显著的系统发育信号（phylogenetic signal）。因此，为确保进化独立性，我们针对每个目、科、属的物种中位值开展了额外的异速生长分析。不同分类层级的分析所得斜率均近似于0.75的缩放比例。据我们所知，哺乳动物脑容量为何会以3/4次方的比例随身体大小缩放，目前仍是未解之谜。针对单个分类目开展的分析，由于类群尺寸范围更小，所得斜率通常小于0.75，取值区间为0.24至0.81，中位斜率为0.64。现存绝大多数哺乳动物的脑容量公开数据仍有待补充……