Some Problems in Proving the Existence of the Universal Common Ancestor of Life on Earth

Although overwhelming circumstantial evidence supports the existence of the universal common ancestor of all extant life on Earth, it is still an open question whether the universal common ancestor existed or not. Theobald (Nature 465, 219–222 (2010)) recently challenged this problem with a formal statistical test applied to aligned sequences of conservative proteins sampled from all domains of life and concluded that the universal common ancestor hypothesis holds. However, we point out that there is a fundamental flaw in Theobald's method which used aligned sequences. We show that the alignment gives a strong bias for the common ancestor hypothesis, and we provide an example that Theobald's method supports a common ancestor hypothesis for two apparently unrelated families of protein-encoding sequences (cytb and nd2 of mitochondria). This arouses suspicion about the effectiveness of the “formal” test

Rooting the eutherian tree: the power and pitfalls of phylogenomics

In an attempt to root the eutherian tree using genome-scale data with the maximum likelihood method, a concatenate analysis supports a putatively wrong tree, whereas separate analyses of different genes reduced the bias