Department of Evolutionary Studies of Biosystems, Graduate University for Advanced Studies, Hayama, Kanagawa, Japan.
Mol Biol Evol. 2012 Jan;29(1):145-56. doi: 10.1093/molbev/msr172. Epub 2011 Sep 8.
There have been conflicting arguments as to what happened in the human-chimpanzee speciation event. Patterson et al. (2006, Genetic evidence for complex speciation of humans and chimpanzees. Nature 441:1103-1108) proposed a hypothesis that the human-chimpanzee speciation event involved a complicated demographic process: that is, the ancestral lineages of humans and chimpanzees experienced temporal isolation followed by a hybridization event. This hypothesis stemmed from two major observations: a wide range of human-chimpanzee nucleotide divergence across the autosomal genome and very low divergence in the X chromosome. In contrast, Innan and Watanabe (2006, The effect of gene flow on the coalescent time in the human-chimpanzee ancestral population. Mol Biol Evol. 23:1040-1047) demonstrated that the null model of instantaneous speciation fits the genome-wide divergence data for the two species better than alternative models involving partial isolation and migration. To reconcile these two conflicting reports, we first reexamined the analysis of autosomal data by Patterson et al. (2006). By providing a theoretical framework for their analysis, we demonstrated that their observation is what is theoretically expected under the null model of instantaneous speciation with a large ancestral population. Our analysis indicated that the observed wide range of autosomal divergence is simply due to the coalescent process in the large ancestral population of the two species. To further verify this, we developed a maximum likelihood function to detect evidence of hybridization in genome-wide divergence data. Again, the null model with no hybridization best fits the data. We conclude that the simplest speciation model with instantaneous split adequately describes the human-chimpanzee speciation event, and there is no strong reason to involve complicated factors in explaining the autosomal data.
关于人类与黑猩猩的物种形成事件究竟发生了什么，一直存在争议。Patterson 等人（2006 年，人类与黑猩猩物种形成的遗传证据。自然 441:1103-1108）提出了一个假设，即人类与黑猩猩的物种形成事件涉及一个复杂的人口过程：即人类和黑猩猩的祖先谱系经历了时间隔离，然后发生了杂交事件。这一假设源于两个主要观察结果：一是整个常染色体基因组中人类与黑猩猩核苷酸的差异范围很广，二是 X 染色体的差异非常低。相比之下，Innan 和 Watanabe（2006 年，基因流对人类-黑猩猩祖先群体合并时间的影响。分子生物学与进化 23:1040-1047）表明，在两个物种的全基因组分歧数据中，瞬时物种形成的零模型比涉及部分隔离和迁移的替代模型更适合。为了调和这两个相互矛盾的报告，我们首先重新检查了 Patterson 等人（2006 年）对常染色体数据的分析。通过为他们的分析提供一个理论框架，我们证明了他们的观察结果在大祖先种群的瞬时物种形成零模型下是理论上可以预期的。我们的分析表明，观察到的广泛的常染色体分歧仅仅是由于两个物种的大祖先种群中的合并过程。为了进一步验证这一点，我们开发了一个最大似然函数来检测全基因组分歧数据中杂交的证据。同样，没有杂交的零模型最适合数据。我们的结论是，最简单的瞬时分裂物种形成模型足以描述人类与黑猩猩的物种形成事件，没有强有力的理由用复杂的因素来解释常染色体数据。
