Department of Anthropology, Buffalo Human Evolutionary Morphology Lab, University at Buffalo, Buffalo, New York, USA.
Am J Phys Anthropol. 2021 Apr;174(4):744-751. doi: 10.1002/ajpa.24219. Epub 2021 Jan 4.
The Giles hypothesis posits that differences in the cranial morphology of Pan troglodytes and Gorilla gorilla are largely the result of allometric scaling. However, previous support for the Giles hypothesis was based on bivariate plots of linear measurements. This investigation uses geometric morphometric methods to retest this hypothesis and its prediction that extending the ontogenetic trajectory of a chimpanzee would produce an adult gorilla-like cranial morphology.
Forty-three 3D cranial landmarks were collected from an ontogenetic series of 76 Pan troglodytes and 58 Gorilla gorilla specimens. Ontogenetic trajectories of cranial shape change were computed via multivariate regression of Procrustes aligned coordinates against LnCS (size vector) and molar eruption stage (developmental vector). These two vectors were then used in developmental simulations to extend the ontogenetic trajectories of adult chimpanzees. Allometric trajectories of chimpanzees and gorillas were also directly compared using Procrustes ANOVA.
Pan and Gorilla significantly differ in their allometric trajectories, and none of the Pan developmental simulations resembled actual adult gorillas. Additionally, the more the Pan developmental vector was extended, the more morphologically distinct the simulations became from actual adult gorillas.
Taken together, these results do not support the Giles hypothesis that allometric scaling is primarily responsible for observed morphological differences between chimpanzee and gorilla crania. This investigation demonstrates that neither "growing" a chimpanzee to the size of a gorilla, nor extending a chimpanzee's developmental shape trajectory will result in an adult gorilla-like cranial morphology as they differ in their patterns of allometry.
Giles 假说认为，黑猩猩和大猩猩颅骨形态的差异主要是由异速生长导致的。然而，之前对 Giles 假说的支持是基于线性测量的双变量图。本研究使用几何形态测量方法重新检验了这一假说及其预测，即延长黑猩猩的个体发育轨迹会产生类似于成年大猩猩的颅骨形态。
从 76 个黑猩猩和 58 个大猩猩的个体发育系列中采集了 43 个 3D 颅骨标志点。通过多元回归分析，将颅骨形状变化的个体发育轨迹与 LnCS（大小向量）和磨牙萌出阶段（发育向量）进行了计算。然后，利用这两个向量在发育模拟中扩展了成年黑猩猩的个体发育轨迹。还使用 Procrustes ANOVA 直接比较了黑猩猩和大猩猩的异速生长轨迹。
黑猩猩和大猩猩在其异速生长轨迹上存在显著差异，并且没有一个黑猩猩发育模拟与实际的成年大猩猩相似。此外，随着黑猩猩发育向量的延伸，模拟与实际成年大猩猩的形态差异变得越来越大。
综上所述，这些结果不支持 Giles 假说，即认为异速生长是导致黑猩猩和大猩猩颅骨形态差异的主要原因。本研究表明，无论是将黑猩猩“生长”到大猩猩的大小，还是延伸黑猩猩的发育形状轨迹，都不会导致成年大猩猩般的颅骨形态，因为它们的异速生长模式不同。
