Common ancestry of life – Q.E.D?

The proposition that “all the organic beings which have ever lived on this earth descended from some one primordial form”, first put forward by Darwin, and central to modern evolutionary theory, is a commonly held biological view.

An attempt by Douglas Theobald, described in a letter to Nature as a ‘formal test’ of the universal common ancestry (UCA) hypothesis, stirred considerable interest recently – whilst the universality of the genetic code and evidence from comparative genomics provide strong support for UCA, the discovery of widespread horizontal gene transfer in eukaryotes has  raised questions over the assumption of universal ancestry.

Theobald tested the UCA hypothesis against alternative ancestry models for the origin of Archaea, Eukarya and Bacteria using a Bayesian analysis of universally conserved protein sequences, and reported "conclusive" support for the common-ancestry hypothesis.

However, in a Commentary article published in Biology Direct, Eugene Koonin and Yuri Wolf report on a statistical procedure which demonstrates how the test results are an artifact of the investigation’s methods, and that if used to test any sufficiently similar sequences, they would yield results in support of ‘common ancestry’ irrespective of the actual evolutionary relatedness. The authors conclude that, although in general the evidence for the UCA hypothesis is effectively irrefutable, and sequence similarity among universal proteins resulting from convergent evolution is a virtual impossibility, a formal demonstration of the UCA independent of any assumptions might not be possible.

The discussion on the origin of life is one which features prominently in Biology Direct, with the journal’s policy of open peer review allowing for an interesting perspective on the discursive nature of this topic between researchers in this field. For more articles of interest please see the thematic series “Origin and early evolution of life”.

Ciaran O’Neill
Senior Journal Development Editor


Theobald, D. L. (2010). A formal test of the theory of universal common ancestry Nature, 465 (7295), 219-222 DOI: 10.1038/nature09014

Koonin, E., & Wolf, Y. (2010). The common ancestry of life Biology Direct, 5 (1) DOI: 10.1186/1745-6150-5-64

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