Mahaney M C, Williams-Blangero S, Blangero J, Leland M M
School of Human Biology, University of Guelph, Ontario, Canada.
Hum Biol. 1993 Dec;65(6):991-1003.
Anthropoid phylogeny has been characterized by dramatic increases in relative brain size. Given the importance of genetic mechanisms in evolution, quantitative genetic analyses of the biological concomitants of relative brain size variation should greatly augment our understanding of this phylogenetic phenomenon. In humans the brain is often linked metabolically with three other organs--heart, kidneys, and liver--that together account for most of the total basal metabolic rate. Because the weights of these four organs are proportional to their individual organ metabolic rates, their summed weights have been used by previous researchers as a proxy measure for their composite organ metabolic rate. We have conducted a quantitative genetic analysis of variation in the relative weights of these four organs in a population of captive baboons from the Southwest Foundation for Biomedical Research. These analyses were performed on loge-transformed organ weights available for 601 animals, 307 of which were assigned to 25 pedigrees containing 2 to 49 members; the remaining 294 animals were treated as independent individuals. Moderate but statistically significant (p < 0.005) heritabilities were estimated for all four organ weights: h2brain = 0.409 +/- 0.147, h2heart = 0.386 +/- 0.184, h2kidneys = 0.468 +/- 0.152, and h2liver = 0.600 +/- 0.160. Significant (p < 0.05) additive genetic correlations were estimated between brain and liver weights (rho G = 0.568) and between liver and kidney weights (rho G = 0.858). Significant (p < 0.05) environmental correlations were identified for heart and kidney weights (rho E = 0.551) and for liver and kidney weights (rho E = 0.684). Our results clearly demonstrate that the four organ weights have substantial heritable components that, because of their similar magnitudes, are probably equally susceptible to selection. However, the patterns of intercorrelation revealed by our analyses of the genetic and environmental correlation matrices indicate that, of the four organs composing the proxy measure of organ metabolic rate, only the liver and the kidneys are likely to exhibit correlated responses to selection for increased relative brain size such as that observed in the anthropoid fossil record.
类人猿的系统发育以相对脑容量的显著增加为特征。鉴于遗传机制在进化中的重要性，对相对脑容量变化的生物学伴随特征进行数量遗传学分析，应能极大地增进我们对这一系统发育现象的理解。在人类中，大脑在代谢上常与其他三个器官——心脏、肾脏和肝脏——相关联，这三个器官共同构成了基础代谢率的大部分。由于这四个器官的重量与其各自的器官代谢率成正比，先前的研究人员已将它们的总重量用作其复合器官代谢率的替代指标。我们对西南生物医学研究基金会圈养的一群狒狒中这四个器官相对重量的变化进行了数量遗传学分析。这些分析是针对601只动物的对数转换后的器官重量进行的，其中307只被分配到25个家系中，每个家系包含2至49个成员；其余294只动物被视为独立个体。对所有四个器官重量均估计出中等但具有统计学意义（p < 0.005）的遗传力：h2脑 = 0.409 ± 0.147，h2心脏 = 0.386 ± 0.184，h2肾脏 = 0.468 ± 0.152，h2肝脏 = 0.600 ± 0.160。估计脑重量与肝脏重量之间（rho G = 0.568）以及肝脏重量与肾脏重量之间（rho G = 0.858）存在显著（p < 0.05）的加性遗传相关性。确定心脏和肾脏重量之间（rho E = 0.551）以及肝脏和肾脏重量之间（rho E = 0.684）存在显著（p < 0.05）的环境相关性。我们的结果清楚地表明，这四个器官的重量具有很大的遗传成分，由于它们的大小相似，可能同样容易受到选择的影响。然而，我们对遗传和环境相关矩阵的分析所揭示的相互关联模式表明，在构成器官代谢率替代指标的四个器官中，只有肝脏和肾脏可能会对相对脑容量增加的选择表现出相关反应，比如在类人猿化石记录中观察到的那样。
