Kirk E Christopher
Department of Anthropology, University of Texas at Austin, 1 University Station C3200, 78712, USA.
J Hum Evol. 2006 Jul;51(1):76-90. doi: 10.1016/j.jhevol.2006.01.005. Epub 2006 Mar 27.
Primates differ from most other mammals in having relatively large brains. As a result, numerous comparative studies have attempted to identify the selective variables influencing primate encephalization. However, none have examined the effect of the total amount of visual input on relative brain size. According to Jerison's principle of proper mass, functional areas of the brain devoted primarily to processing visual information should exhibit increases in size when the amount of visual input to those areas increases. As a result, the total amount of visual input to the brain could exert a large influence on encephalization because visual areas comprise a large proportion of total brain mass in primates. The goal of this analysis is to test the expectation of a direct relationship between visual input and encephalization using optic foramen size and optic nerve size as proxies for total visual input. Data were collected for a large comparative sample of primates and carnivorans, and three primary analyses were undertaken. First, the relationship between relative proxies for visual input and relative endocranial volume were examined using partial correlations and phylogenetic comparative methods. Second, to examine the generality of the results derived for extant primates, a parallel series of partial correlation and comparative analyses were undertaken using data for carnivorans. Third, data for various Eocene and Oligocene primates were compared with those for living primates in order to determine whether the fossil taxa demonstrate a similar relationship between relative brain size and visual input. All three analyses confirm the expectations of proper mass and favor the conclusion that the amount of visual input has been a major influence on the evolution of relative brain size in both primates and carnivorans. Furthermore, this study suggests that differences in visual input may partly explain (1) the high encephalization of primates relative to the primitive eutherian condition, (2) the high encephalization of extant anthropoids relative to other primates, and (3) the very low encephalization of Eocene adapiforms.
灵长类动物与大多数其他哺乳动物不同，它们的大脑相对较大。因此，许多比较研究试图确定影响灵长类动物脑化的选择变量。然而，没有人研究过视觉输入总量对相对脑大小的影响。根据杰里森的适当质量原则，主要用于处理视觉信息的大脑功能区域，当输入这些区域的视觉信息量增加时，其大小应该会增加。因此，大脑的视觉输入总量可能对脑化有很大影响，因为在灵长类动物中，视觉区域在大脑总质量中占很大比例。本分析的目的是使用视神经孔大小和视神经大小作为总视觉输入的代理指标，来检验视觉输入与脑化之间存在直接关系的预期。收集了大量灵长类动物和食肉动物的比较样本数据，并进行了三项主要分析。首先，使用偏相关和系统发育比较方法，研究视觉输入的相对代理指标与相对颅内容积之间的关系。其次，为了检验从现存灵长类动物得出的结果的普遍性，使用食肉动物的数据进行了一系列平行的偏相关和比较分析。第三，将各种始新世和渐新世灵长类动物的数据与现存灵长类动物的数据进行比较，以确定化石分类群在相对脑大小和视觉输入之间是否表现出类似的关系。所有这三项分析都证实了适当质量的预期，并支持这样的结论，即视觉输入量对灵长类动物和食肉动物相对脑大小的进化都有重大影响。此外，这项研究表明，视觉输入的差异可能部分解释了：（1）灵长类动物相对于原始真兽类状况的高脑化；（2）现存类人猿相对于其他灵长类动物的高脑化；（3）始新世狐猴类的极低脑化。
