Hofman M A
Brain Behav Evol. 1985;27(1):28-40. doi: 10.1159/000118718.
The evolution of the brain in mammals has been accompanied by a progressive enlargement of the cerebral cortex. Allometric analysis of the volume, surface and convolutedness of this cortex shows that among mammals two major groups can be distinguished: (1) species with lissencephalic brains, where surface-volume relationships are determined by linear geometric laws, and (2) species with gyrencephalic brains, where strict geometric similarity no longer applies. Different mathematical models are required to describe the brain morphology in these groups. It has been shown, moreover, that among species with convoluted brains, marine mammals (Cetacea) form a subgroup in that the cerebrocortical surface in these animals is more folded than in terrestrial mammals of similar brain size. Thus it appears that the use of a single allometric relation in studying the effect of size increase on the geometry of the brain - irrespective of convolutedness or ecological strategy - as has been done in previous studies, is unjustified and obscures the differences in the structural organization of mammalian brains. Finally, a dimensionless index of cortical folding is proposed, which indicates that the degree of cortical folding depends not only on the volume of the brain or cortex but on cortical thickness as well.
哺乳动物大脑的进化伴随着大脑皮层的逐渐扩大。对该皮层的体积、表面积和卷曲程度进行的异速生长分析表明，在哺乳动物中可区分出两大类：（1）无脑回的物种，其表面积与体积的关系由线性几何定律决定；（2）有脑回的物种，严格的几何相似性不再适用。需要不同的数学模型来描述这些类群中的大脑形态。此外，研究表明，在有脑回的物种中，海洋哺乳动物（鲸目）形成一个亚群，因为这些动物的脑皮质表面比脑大小相似的陆生哺乳动物的更褶皱。因此，正如先前研究中所做的那样，在研究大脑大小增加对大脑几何形状的影响时使用单一的异速生长关系——无论是否有脑回或生态策略——是不合理的，并且掩盖了哺乳动物大脑结构组织的差异。最后，提出了一个皮层折叠的无量纲指数，该指数表明皮层折叠程度不仅取决于大脑或皮层的体积，还取决于皮层厚度。
