Institute of Cognitive and Evolutionary Anthropology, University of Oxford, Oxford OX2 6PN, United Kingdom.
Proc Natl Acad Sci U S A. 2010 Dec 14;107(50):21582-6. doi: 10.1073/pnas.1005246107. Epub 2010 Nov 22.
Evolutionary encephalization, or increasing brain size relative to body size, is assumed to be a general phenomenon in mammals. However, despite extensive evidence for variation in both absolute and relative brain size in extant species, there have been no explicit tests of patterns of brain size change over evolutionary time. Instead, allometric relationships between brain size and body size have been used as a proxy for evolutionary change, despite the validity of this approach being widely questioned. Here we relate brain size to appearance time for 511 fossil and extant mammalian species to test for temporal changes in relative brain size over time. We show that there is wide variation across groups in encephalization slopes across groups and that encephalization is not universal in mammals. We also find that temporal changes in brain size are not associated with allometric relationships between brain and body size. Furthermore, encephalization trends are associated with sociality in extant species. These findings test a major underlying assumption about the pattern and process of mammalian brain evolution and highlight the role sociality may play in driving the evolution of large brains.
进化性脑化，即大脑相对于身体大小的增长，被认为是哺乳动物的普遍现象。然而，尽管现存物种的大脑绝对和相对大小存在广泛的变异证据，但对于进化过程中大脑大小变化的模式还没有明确的测试。相反，大脑大小与身体大小之间的比例关系一直被用作进化变化的替代指标，尽管这种方法的有效性受到广泛质疑。在这里，我们将 511 种化石和现存哺乳动物的大脑大小与出现时间相关联，以检验相对大脑大小随时间的变化。我们表明，在不同的群体中，脑化斜率存在广泛的差异，并且哺乳动物的脑化并不是普遍的。我们还发现，大脑大小的时间变化与大脑和身体大小之间的比例关系无关。此外，现存物种中脑化趋势与社会性有关。这些发现检验了关于哺乳动物大脑进化模式和过程的一个主要假设，并强调了社会性在推动大脑进化中的作用。
