Taylor Andrea B, van Schaik Carel P
Doctor of Physical Therapy Division, Department of Community and Family Medicine, Duke University School of Medicine, USA.
J Hum Evol. 2007 Jan;52(1):59-71. doi: 10.1016/j.jhevol.2006.07.010. Epub 2006 Aug 8.
Numerous hypotheses have been advanced to explain relative increases in brain size in primates and other mammals. However, notably less attention has been directed towards addressing the biological limits to increasing brain size. Here we explore variation in brain size in orangutans. We evaluated both raw and size-adjusted cranial capacity (CC) in adult Pongo pygmaeus pygmaeus (n=147), P. p. wurmbii (n=24), P. p. morio (n=14), and P. abelii (n=36). Results demonstrate significant variation in CC among orangutan taxa. Population differences in raw CC are significant for females (p=0.014) but not males. Post-hoc pairwise comparisons among females further reveal that raw CC is significantly smaller in P. p. morio compared to both P. abelii and P. p. pygmaeus. When evaluated for proportionality, geometric equivalence in CC is not maintained in orangutans, as P. p. morio has a significantly smaller CC when compared to one or more other orangutan groups. Even after statistically partitioning size and size-correlated shape, P. p. morio has a significantly smaller CC compared to most other orangutan groups. These observed differences in relative brain size are consistent with known variation in resource quality and life history amongst orangutan populations. Specifically, P. p. morio is characterized by the least productive habitat, the lowest energy intake during extended lean periods, and the shortest interbirth intervals. Our results, therefore, provide conditional support for the hypothesis that decreased brain size is related to prolonged episodes of food scarcity, and suggest a correlation between brain size, diet quality, and life history at the lowest macroevolutionary level. The association of a relatively small brain and poor diet quality in Pongo further suggests that ecological factors may plausibly account for such a reduction in brain size as observed in the recently recovered Homo floresiensis from Indonesia.
人们已经提出了许多假说，来解释灵长类动物和其他哺乳动物大脑尺寸的相对增加。然而，对于解决大脑尺寸增加的生物学限制，所给予的关注明显较少。在这里，我们探讨了红毛猩猩大脑尺寸的变化。我们评估了成年苏门答腊猩猩（Pongo pygmaeus pygmaeus，n = 147）、婆罗洲猩猩（P. p. wurmbii，n = 24）、达班努里猩猩（P. p. morio，n = 14）和阿比力猩猩（P. abelii，n = 36）的原始颅容量（CC）和经大小调整后的颅容量。结果表明，不同红毛猩猩分类群之间的颅容量存在显著差异。雌性红毛猩猩的原始颅容量存在显著的种群差异（p = 0.014），但雄性则没有。雌性红毛猩猩之间的事后两两比较进一步显示，达班努里猩猩的原始颅容量明显小于阿比力猩猩和苏门答腊猩猩。在评估比例关系时，红毛猩猩的颅容量并不保持几何等价，因为与一个或多个其他红毛猩猩群体相比，达班努里猩猩的颅容量明显更小。即使在对大小和与大小相关的形状进行统计划分之后，达班努里猩猩的颅容量仍明显小于大多数其他红毛猩猩群体。这些观察到的相对脑容量差异，与红毛猩猩种群中已知的资源质量和生活史变化相一致。具体而言，达班努里猩猩的特点是栖息地生产力最低、在漫长的食物匮乏期能量摄入最低，以及产仔间隔最短。因此，我们的结果为大脑尺寸减小与长期食物短缺有关这一假说提供了有条件的支持，并表明在最低的宏观进化水平上，脑容量、饮食质量和生活史之间存在相关性。红毛猩猩中相对较小的大脑与较差的饮食质量之间的关联，进一步表明生态因素可能合理地解释了在最近从印度尼西亚发现的弗洛勒斯人（Homo floresiensis）中观察到的大脑尺寸减小现象。
