据新科学家网站报道，华盛顿大学的科学家新完成的一项研究表明，在250万年前现代人类从南方古猿中分离出来时，人类的某个基因发生了复制，改变了人类大脑进化的方式。这个复制出来的额外基因拷贝SRGAP2的作用是驱动新大脑皮层的发育，它降低了大脑的发育速度，从而使神经元有更充分的时间进行发育并彼此间建立连接。据报道，该研究团队发现，SRGAP2基因在350万年前对其自身进行了复制，正是人类与黑猩猩在进化上分开之后。在此100万年后，这个子代基因又对其自身进行了复制从而产生了第三代拷贝。所有的这三个基因共存在现代人类中。
人猿揖别时，SRGAP2基因也进行了复制
当研究人员将人类的该基因打入小鼠时，其所产生的蛋白质结合到初始的SRGAP2基因拷贝上，阻止该基因发挥功能。研究人员说：“不过这种遗传破坏的作用是让大脑有充分的时间进行发育。尽管小鼠的大脑本身就不会发育的太大，不过新皮层中的神经元变得更像是大脑细胞，长出粗大的棘突在彼此间进行信息交换。”现在，研究人员计划将复制的基因转到绒猴中，以研究这种动物的行为是否会因大脑持续的复杂化而发生改变。
Evolution of Human-Specific Neural SRGAP2 Genes by Incomplete Segmental Duplication
Megan Y. Dennis, Xander Nuttle, Peter H. Sudmant, Francesca Antonacci, Tina A. Graves, Mikhail Nefedov, Jill A. Rosenfeld, Saba Sajjadian, Maika Malig, Holland Kotkiewicz, Cynthia J. Curry, Susan Shafer, Lisa G. Shaffer, Pieter J. de Jong, Richard K. Wilson, Evan E. Eichler
Gene duplication is an important source of phenotypic change and adaptive evolution. We leverage a haploid hydatidiform mole to identify highly identical sequences missing from the reference genome, confirming that the cortical development gene Slit-Robo Rho GTPase-activating protein 2 (SRGAP2) duplicated three times exclusively in humans. We show that the promoter and first nine exons of SRGAP2 duplicated from 1q32.1 (SRGAP2A) to 1q21.1 (SRGAP2B) ∼3.4 million years ago (mya). Two larger duplications later copied SRGAP2B to chromosome 1p12 (SRGAP2C) and to proximal 1q21.1 (SRGAP2D) ∼2.4 and ∼1 mya, respectively. Sequence and expression analyses show that SRGAP2C is the most likely duplicate to encode a functional protein and is among the most fixed human-specific duplicate genes. Our data suggest a mechanism where incomplete duplication created a novel gene function—antagonizing parental SRGAP2 function—immediately “at birth” 2–3 mya, which is a time corresponding to the transition from Australopithecus to Homo and the beginning of neocortex expansion.
