Department of Genetics, Southwest Foundation for Biomedical Research, 7620 N.W. Loop 410, San Antonio, TX 78227, USA.
Neuroimage. 2010 Nov 15;53(3):1103-8. doi: 10.1016/j.neuroimage.2010.02.020. Epub 2010 Feb 20.
Understanding the evolutionary forces that produced the human brain is a central problem in neuroscience and human biology. Comparisons across primate species show that both brain volume and gyrification (the degree of folding in the cerebral cortex) have progressively increased during primate evolution and there is a strong positive correlation between these two traits across primate species. The human brain is exceptional among primates in both total volume and gyrification, and therefore understanding the genetic mechanisms influencing variation in these traits will improve our understanding of a landmark feature of our species. Here we show that individual variation in gyrification is significantly heritable in both humans and an Old World monkey (baboons, Papio hamadryas). Furthermore, contrary to expectations based on the positive phenotypic correlation across species, the genetic correlation between cerebral volume and gyrification within both humans and baboons is estimated as negative. These results suggest that the positive relationship between cerebral volume and cortical folding across species cannot be explained by one set of selective pressures or genetic changes. Our data suggest that one set of selective pressures favored the progressive increase in brain volume documented in the primate fossil record, and that a second independent selective process, possibly related to parturition and neonatal brain size, may have favored brains with progressively greater cortical folding. Without a second separate selective pressure, natural selection favoring increased brain volume would be expected to produce less folded, more lissencephalic brains. These results provide initial evidence for the heritability of gyrification, and possibly a new perspective on the evolutionary mechanisms underlying long-term changes in the nonhuman primate and human brain.
理解产生人类大脑的进化力量是神经科学和人类生物学的核心问题。对灵长类物种的比较表明，大脑体积和脑回（大脑皮层的折叠程度）在灵长类进化过程中逐渐增加，并且在灵长类物种之间这两个特征之间存在强烈的正相关关系。人类大脑在总体积和脑回方面都在灵长类中是特殊的，因此，了解影响这些特征变化的遗传机制将提高我们对我们物种标志性特征的理解。在这里，我们表明，脑回的个体变异在人类和一种旧大陆猴（狒狒，Papio hamadryas）中均具有显著的遗传性。此外，与跨物种表型相关性的预期相反，人类和狒狒内部大脑体积和脑回之间的遗传相关性估计为负相关。这些结果表明，跨物种大脑体积和皮质折叠之间的正相关关系不能仅用一组选择压力或遗传变化来解释。我们的数据表明，一组选择压力有利于在灵长类化石记录中记录的大脑体积的逐步增加，而第二个独立的选择过程可能与分娩和新生儿大脑大小有关，可能有利于具有更大皮质折叠的大脑。如果没有第二个独立的选择压力，自然选择有利于增加大脑体积，预计会产生较少折叠、更平滑的大脑。这些结果为脑回的遗传性提供了初步证据，并为非人类灵长类动物和人类大脑长期变化的进化机制提供了新的视角。
