TRENDS in Genetics Vol.20 No.2 February 2004
Reading the entrails of chickens: molecular timescales of evolution and the illusion of precision
Dan Graur 1 and William Martin 2
1 Department of Biology and Biochemistry, University of Houston, Houston, TX 77204-5001, USA
2 Institut für Botanik III, Heinrich-Heine Universität Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany
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For almost a decade now, a team of molecular evolutionists has produced a plethora of seemingly precise molecular clock estimates for divergence events ranging from the speciation of cats and dogs to lineage separations that might have occurred, 4 billion years ago. Because the appearance of accuracy has an irresistible allure, non-specialists frequently treat these estimates as factual. In this article, we show that all of these divergence-time estimates were generated through improper methodology on the basis of a single calibration point that has been unjustly denuded of error. The illusion of precision was achieved mainly through the conversion of statistical estimates (which by definition possess standard errors, ranges and confidence intervals) into errorless numbers. By employing such techniques successively, the time estimates of even the most ancient divergence events were made to look deceptively precise. For example, on the basis of just 15 genes, the arthropod–nematode divergence event was ‘calculated’ to have occurred 1167 more or less 83 million years ago (i.e. within a 95% confidence interval of ~350 million years). Were calibration and derivation uncertainties taken into proper consideration, the 95% confidence interval would have turned out to be at least 40 times larger (~14.2 billion years).
‘We demand rigidly defined areas of doubt and uncertainty.’ Douglas Adams
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