Testing for universal common ancestry

A phylogenetic model selection test to quantify the evidence for the Universal Common Ancestry (UCA) of life forms was proposed recently (Theobald 2010a), based on the comparison of the statistical support, using likelihoods, the Akaike Information Criterion (AIC), or Bayes factors, for two different phylogenetic models representing the UCA and the independent origins (IOs) hypotheses (Sober and Steel 2002). In this test, the former is represented by a single phylogeny connecting all sequences, whereas the latter is depicted by several, independent phylogenetic trees (Fig. 1). Importantly, in the original UCA test, the same alignment was used to represent both hypotheses. When applied to a particular data set of 23 universally conserved proteins, the test strongly favored a UCA scenario.