Abstract # 177:

Scheduled for Monday, September 21, 2009 09:15 AM-09:25 AM: Session 16 (Mission Bay Ballroom AB) Oral Presentation


J. Rogers1,2, P. Kochunov3, K. Zilles4, W. Shelledy5, J. Lancaster3, P. M. Thompson6, R. Duggirala5, J. Blangero5, P. T. Fox3 and D. C. Glahn3
1Baylor College of Medicine, Human Genome Sequencing Center, Houston, TX 77030, USA, 2Southwest National Primate Research Center, San Antonio TX, 3Research Imaging Center, UTHSC-SA, San Antonio TX, 4Institute of Neuroscience and Medicine, Research Centre Julich Germany, 5Dept. of Genetics, Southwest Foundation, San Antonio TX, 6Laboratory of Neuro Imaging, UCLA School of Medicine, Los Angeles CA

Understanding the evolutionary forces that produced the nonhuman primate and human brains is a central problem in comparative biology, biological anthropology and neuroscience. Comparisons across primate species show both brain volume and gyrification (degree of folding in the cerebral cortex) have increased dramatically during primate evolution and there is a strong positive correlation between these two traits across species. Prior studies demonstrated that brain volume is significantly heritable. Here we show that individual variation in gyrification measured from MRI scans exhibits significant additive genetic heritability in pedigrees of both humans [Homo sapiens, n=242, h2=0.30, p=0.018] and baboons [Papio hamadryas, n=97, h2=0.71, p=0.002]. We also find that, contrary to expectations from the positive phenotypic correlation across species, genetic correlations between cerebral volume and gyrification within both humans and baboons are negative [baboons: ρG=-0.77; humans: ρG=-0.73]. This demonstrates that the positive relationship between cerebral volume and cortical folding observed across primate species cannot be explained by a single set of selective pressures or genetic changes. We conclude that one set of selective pressures produced the progressive increase in brain volume observed during primate evolution, and a different selective process, possibly related to parturition and limitations on neonatal brain size, favored brains with progressively greater cortical folding. These results provide new perspective on the mechanisms underlying long-term evolutionary changes in nonhuman primate and human brains.