Department of Biological Sciences, The University of Tokyo, , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Proc Biol Sci. 2013 Apr 17;280(1760):20130338. doi: 10.1098/rspb.2013.0338. Print 2013 Jun 7.
The extremely small endocranial volume (ECV) of LB1, the type specimen of Homo floresiensis, poses a challenge in our understanding of human brain evolution. Some researchers hypothesize dramatic dwarfing of relative brain size from Homo erectus presumably without significant decrease in intellectual function, whereas others expect a lesser degree of brain diminution from a more primitive, small-brained form of hominin currently undocumented in eastern Asia. However, inconsistency in the published ECVs for LB1 (380-430 cc), unclear human intraspecific brain-body size scaling and other uncertainties have hampered elaborative modelling of its brain size reduction. In this study, we accurately determine the ECV of LB1 using high-resolution micro-CT scan. The ECV of LB1 thus measured, 426 cc, is larger than the commonly cited figure in previous studies (400 cc). Coupled with brain-body size correlation in Homo sapiens calculated based on a sample from 20 worldwide modern human populations, we construct new models of the brain size reduction in the evolution of H. floresiensis. The results show a more significant contribution of scaling effect than previously claimed.
极度缩小的 LB1 （弗洛里斯人模式标本）的内颅容量（ECV），对我们理解人类大脑进化构成了挑战。一些研究人员假设，相对大脑尺寸从直立人显著缩小，而智力功能没有明显下降，而另一些人则期望大脑缩小程度较小，来自目前在东亚尚未记录的更原始、脑容量较小的原始人形式。然而，LB1 的已发表的 ECV 不一致（380-430 cc），人类种内大脑-身体大小比例的不明确以及其他不确定性，阻碍了对其大脑缩小的详细建模。在这项研究中，我们使用高分辨率微 CT 扫描准确确定 LB1 的 ECV。因此，测量得到的 LB1 的 ECV 为 426 cc，大于之前研究中常用的数值（400 cc）。结合从 20 个全球现代人类群体中计算的智人大脑-身体大小相关性，我们构建了弗洛里斯人进化过程中大脑缩小的新模型。结果表明，与之前声称的相比，缩放效应的贡献更为显著。
