Alba David M
Institut Català de Paleontologia, Universitat Autònoma de Barcelona, Edifici ICP, Campus de la UAB s/n, Cerdanyola del Vallès, Barcelona, Spain.
J Anthropol Sci. 2010;88:11-48.
Paleobiological inferences on general cognitive abilities (intelligence) in fossil hominoids strongly rely on relative brain size or encephalization, computed by means of allometric residuals, quotients or constants. Th is has been criticized on the basis that it presumably fails to reflect the higher intelligence of great apes, and absolute brain size has been favored instead. Many problems of encephalization metrics stem from the decrease of allometric slopes towards lower taxonomic level, thus making it difficult to determine at what level encephalization metrics have biological meaning. Here, the hypothesis that encephalization can be used as a good neuroanatomical proxy for intelligence is tested at two different taxonomic levels. A significant correlation is found between intelligence and encephalization only at a lower taxonomic level, i.e. on the basis of a low allometric slope, irrespective of whether species data or independent contrasts are employed. This indicates that higher-level slopes, resulting from encephalization grade shifts between subgroups (including hylobatids vs. great apes), do not reflect functional equivalence, whereas lower-level metrics can be employed as a paleobiological proxy for intelligence. Thus, in accordance to intelligence rankings, lower-level metrics indicate that great apes are more encephalized than both monkeys and hylobatids. Regarding fossil taxa, encephalization increased during hominin evolution (particularly in Homo), but during the Miocene a significant shift towards higher encephalization (and inferred enhanced cognitive abilities) must have been also involved in the emergence of the great-ape-and-human clade (Hominidae). This is confirmed by the modern great-ape-like degree of encephalization displayed by the fossil great ape Hispanopithecus, which contrasts with the rather hylobatid-like degree of the stem hominoid Proconsul. The similarly low encephalization of Oreopithecus might result from secondary reduction under insularity conditions, but the australopith-like degree of encephalization of Homo floresiensis seems incompatible with the cognitive abilities inferred from the stone tools attributed to this taxon.
关于化石类人猿一般认知能力（智力）的古生物学推断，很大程度上依赖于通过异速生长残差、商数或常数计算得出的相对脑容量或脑化程度。这一方法受到了批评，因为它可能无法反映出类人猿较高的智力水平，因此有人更倾向于使用绝对脑容量。脑化程度指标的许多问题源于异速生长斜率朝着较低分类水平下降，从而难以确定脑化程度指标在何种水平上具有生物学意义。在此，我们在两个不同的分类水平上检验了脑化程度可作为智力良好神经解剖学指标的假设。仅在较低分类水平上，即基于低异速生长斜率，无论使用物种数据还是独立对比，都发现智力与脑化程度之间存在显著相关性。这表明，亚组之间脑化程度等级变化（包括长臂猿与类人猿之间）所产生的较高水平斜率并不能反映功能等效性，而较低水平指标可作为智力的古生物学指标。因此，根据智力排名，较低水平指标表明类人猿比猴子和长臂猿的脑化程度更高。关于化石分类群，在人类进化过程中脑化程度增加（特别是在智人中），但在中新世，类人猿和人类分支（人科）的出现肯定也涉及向更高脑化程度（以及推断的认知能力增强）的显著转变。这一点得到了化石类人猿西班牙古猿所显示的现代类人猿样脑化程度的证实，它与原康修尔猿这种原始类人猿相当类似长臂猿的脑化程度形成对比。奥氏猴类似的低脑化程度可能是岛屿环境下二次退化的结果，但弗洛勒斯人似南方古猿的脑化程度似乎与该分类群所制造石器推断出其认知能力不相符。
