National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA.
Biol Direct. 2010 Nov 18;5:64. doi: 10.1186/1745-6150-5-64.
It is common belief that all cellular life forms on earth have a common origin. This view is supported by the universality of the genetic code and the universal conservation of multiple genes, particularly those that encode key components of the translation system. A remarkable recent study claims to provide a formal, homology independent test of the Universal Common Ancestry hypothesis by comparing the ability of a common-ancestry model and a multiple-ancestry model to predict sequences of universally conserved proteins.
We devised a computational experiment on a concatenated alignment of universally conserved proteins which shows that the purported demonstration of the universal common ancestry is a trivial consequence of significant sequence similarity between the analyzed proteins. The nature and origin of this similarity are irrelevant for the prediction of "common ancestry" of by the model-comparison approach. Thus, homology (common origin) of the compared proteins remains an inference from sequence similarity rather than an independent property demonstrated by the likelihood analysis.
A formal demonstration of the Universal Common Ancestry hypothesis has not been achieved and is unlikely to be feasible in principle. Nevertheless, the evidence in support of this hypothesis provided by comparative genomics is overwhelming.
地球上所有的生命形式都有共同的起源，这是一种普遍的观点。这种观点得到了遗传密码的普遍性和多个基因的普遍保守性的支持，特别是那些编码翻译系统关键组件的基因。最近一项引人注目的研究通过比较共同祖先模型和多祖先模型预测普遍保守蛋白序列的能力，声称提供了对普遍共同祖先假说的正式、同源无关的检验。
我们在普遍保守蛋白的串联比对上进行了计算实验，结果表明，所声称的普遍共同祖先的证明是分析蛋白之间显著序列相似性的一个简单结果。该相似性的性质和来源对于模型比较方法预测“共同祖先”的能力并不重要。因此，同源性（共同起源）仍然是从序列相似性推断出来的，而不是由似然分析证明的独立特性。
普遍共同祖先假说的正式证明尚未实现，从原则上讲也不太可能实现。然而，比较基因组学提供的支持这一假说的证据是压倒性的。
