Lee James J, McGue Matt, Iacono William G, Michael Andrew M, Chabris Christopher F
Department of Psychology, University of Minnesota Twin Cities, 75 East River Parkway, Minneapolis, MN 55455, USA.
Geisinger Health System, 120 Hamm Drive Suite 2A, Lewisburg, PA 17837, USA.
Intelligence. 2019 Jul-Aug;75:48-58. doi: 10.1016/j.intell.2019.01.011. Epub 2019 May 7.
There exists a moderate correlation between MRI-measured brain size and the general factor of IQ performance (), but the question of whether the association reflects a theoretically important causal relationship or spurious confounding remains somewhat open. Previous small studies ( < 100) looking for the persistence of this correlation within families failed to find a tendency for the sibling with the larger brain to obtain a higher test score. We studied the within-family relationship between brain volume and intelligence in the much larger sample provided by the Human Connectome Project ( = 1,022) and found a highly significant correlation (disattenuated = 0.18, < .001). We replicated this result in the Minnesota Center for Twin and Family Research ( = 2,698), finding a highly significant within-family correlation between head circumference and intelligence (disattenuated = 0.19, < .001). We also employed novel methods of causal inference relying on summary statistics from genome-wide association studies (GWAS) of head size ( ≈ 10,000) and measures of cognition (257,000 < < 767,000). Using bivariate LD Score regression, we found a genetic correlation between intracranial volume (ICV) and years of education () of 0.41 ( < .001). Using the Latent Causal Variable method, we found a genetic causality proportion of 0.72 ( < .001); thus the genetic correlation arises from an asymmetric pattern, extending to sub-significant loci, of genetic variants associated with ICV also being associated with but many genetic variants associated with not being associated with ICV. This is the pattern of genetic results expected from a causal effect of brain size on intelligence. These findings give reason to take up the hypothesis that the dramatic increase in brain volume over the course of human evolution has been the result of natural selection favoring general intelligence.
磁共振成像测量的脑容量与智商表现的一般因素之间存在中等程度的相关性（），但这种关联反映的是理论上重要的因果关系还是虚假的混杂因素，这个问题在一定程度上仍未明确。之前一些规模较小的研究（样本量<100）试图探寻这种相关性在家庭内部是否持续存在，但未发现脑容量较大的兄弟姐妹有获得更高测试分数的倾向。我们利用人类连接组计划提供的更大样本（=1022）研究了家庭内部脑容量与智力之间的关系，发现了高度显著的相关性（校正衰减后=0.18，<.001）。我们在明尼苏达双胞胎与家庭研究中心（=2698）重复了这一结果，发现头围与智力之间在家庭内部存在高度显著的相关性（校正衰减后=0.19，<.001）。我们还采用了基于全基因组关联研究（GWAS）头围（≈10000）和认知测量（257000<<767000）汇总统计数据的新型因果推断方法。使用双变量LD评分回归，我们发现颅内体积（ICV）与受教育年限（）之间的遗传相关性为0.41（<.001）。使用潜在因果变量方法，我们发现遗传因果比例为0.72（<.001）；因此，遗传相关性源于一种不对称模式，即与ICV相关的遗传变异也与相关，但许多与相关的遗传变异与ICV不相关，这种模式延伸到了次显著位点。这是脑容量对智力产生因果效应所预期的遗传结果模式。这些发现为接受这样一种假设提供了理由，即人类进化过程中脑容量的急剧增加是自然选择青睐一般智力的结果。
