“普遍共同祖先”是说所有陆地生命在基因上都是相关联的，用达尔文的话说就是，都来自某种“温暖的小池塘”。这种观点已成为现代进化论的中心思想。关于“普遍共同祖先”的经典证据很多，但大都是定性的，而且该理论也很少接受正式的、定量的验证。
“普遍共同祖先”观点（简称“UCA观点”）因很多生物中大量横向基因转移的存在而受到质疑。Douglas Theobald将“UCA观点”称之为一个正式假设，并利用对普遍保守蛋白的序列所做的Bayesian统计分析对其进行了验证，同时还将所获得的结果与其他模型（在这些模型中，基因相似性并不被假设能够反映系统发生上的相关性）进行了对比。
最后的结果是，“UCA观点”胜出。生命的单一起源的可能性要远远大于任何其他假设。（生物谷Bioon.com）
生物谷推荐原文出处：
Nature doi:10.1038/nature09014
A formal test of the theory of universal common ancestry
Douglas L. Theobald 1
1 Department of Biochemistry, Brandeis University, Waltham, Massachusetts 01778, USA
Universal common ancestry (UCA) is a central pillar of modern evolutionary theory1. As first suggested by Darwin2, the theory of UCA posits that all extant terrestrial organisms share a common genetic heritage, each being the genealogical descendant of a single species from the distant past3, 4, 5, 6. The classic evidence for UCA, although massive, is largely restricted to ‘local’ common ancestry—for example, of specific phyla rather than the entirety of life—and has yet to fully integrate the recent advances from modern phylogenetics and probability theory. Although UCA is widely assumed, it has rarely been subjected to formal quantitative testing7, 8, 9, 10, and this has led to critical commentary emphasizing the intrinsic technical difficulties in empirically evaluating a theory of such broad scope1, 5, 8, 9, 11, 12, 13, 14, 15. Furthermore, several researchers have proposed that early life was characterized by rampant horizontal gene transfer, leading some to question the monophyly of life11, 14, 15. Here I provide the first, to my knowledge, formal, fundamental test of UCA, without assuming that sequence similarity implies genetic kinship. I test UCA by applying model selection theory5, 16, 17 to molecular phylogenies, focusing on a set of ubiquitously conserved proteins that are proposed to be orthologous. Among a wide range of biological models involving the independent ancestry of major taxonomic groups, the model selection tests are found to overwhelmingly support UCA irrespective of the presence of horizontal gene transfer and symbiotic fusion events. These results provide powerful statistical evidence corroborating the monophyly of all known life.
