Common ancestry put to the test

Abstract

The question of whether or not all life on Earth has an ultimate common origin is a subtle one, complicated by the phenomenon of lateral gene transfer. It has now been tackled with a formal statistical analysis. Universal common ancestry (UCA), the idea that all terrestrial life is genetically related, from some “warm little pond” as Darwin put it, has become central to modern evolutionary theory. The classic evidence for UCA is extensive, but largely qualitative, and the theory is rarely subjected to a formal, quantitative test. And the UCA view has been called into question by the existence of extensive horizontal gene transfer in many organisms. Douglas Theobald has framed the UCA view as a formal hypothesis and put it to the test using Bayesian statistical analysis of the sequences of universally conserved proteins and contrasting the results with alternative models where genetic similarity is not assumed to reflect phylogenetic relatedness. The UCA view wins out: a single origin of life is overwhelmingly more likely than any competing hypothesis.