More genes underwent positive selection in chimpanzee evolution than in human evolution
More genes underwent positive selection in chimpanzee evolution than in human evolution
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DOI：
10.1073/pnas.0701705104
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发表时间：
2007-05-01
影响因子：
11.1
通讯作者：
Zhang, Jianzhi
中科院分区：
文献类型：
--
作者：
Bakewell, Margaret A.;Shi, Peng;Zhang, Jianzhi
在人类进化过程中观察到众多显著且可能是适应性的表型改变，这促使人们普遍认为，自600 - 700万年前人类与黑猩猩进化分异以来，人类谱系中经历达尔文正选择的基因比黑猩猩谱系中的要多。在此，我们通过分析人类和黑猩猩的近14000个基因来检验这一假设。为确保准确且无偏的比较，我们选择了合适的外类群，避免测序错误，并验证了统计方法。我们的结果显示，尽管人类的非同义替换率普遍较高，但人类中受到正选择的基因数量明显少于黑猩猩。这些观察结果可以通过人类由于长期有效种群规模较小而导致自然选择效力降低来解释，但反驳了以人类为中心的观点，即达尔文选择的大幅增强是人类起源的基础。尽管人类和黑猩猩的正选择基因具有不同的分子功能并参与不同的生物过程，但这些差异与人们普遍认为的这些物种的适应性并不明显相符，这表明目前对于哪些性状受到了正选择所知甚少。我们对已确定的正选择基因的分析支持了人类孟德尔疾病与过去适应性之间的关联，但没有为染色体物种形成假说或人类起源的广泛脑基因加速假说提供证据。
Observations of numerous dramatic and presumably adaptive phenotypic modifications during human evolution prompt the common belief that more genes have undergone positive Darwinian selection in the human lineage than in the chimpanzee lineage since their evolutionary divergence 6-7 million years ago. Here, we test this hypothesis by analyzing nearly 14,000 genes of humans and chimps. To ensure an accurate and unbiased comparison, we select a proper outgroup, avoid sequencing errors, and verify statistical methods. Our results show that the number of positively selected genes is substantially smaller in humans than in chimps, despite a generally higher nonsynonymous substitution rate in humans. These observations are explainable by the reduced efficacy of natural selection in humans because of their smaller long-term effective population size but refute the anthropocentric view that a grand enhancement in Darwinian selection underlies human origins. Although human and chimp positively selected genes have different molecular functions and participate in different biological processes, the differences do not ostensibly correspond to the widely assumed adaptations of these species, suggesting how little is currently known about which traits have been under positive selection. Our analysis of the identified positively selected genes lends support to the association between human Mendelian diseases and past adaptations but provides no evidence for either the chromosomal speciation hypothesis or the widespread brain-gene acceleration hypothesis of human origins.