Sunday, February 28, 2010
Graur, D. and W. Martin. 2004. Reading the entrails of chickens: molecular timescales of evolution and the illusion of precision. TRENDS in Genetics. 20(2): 80-86.
The purpose of this paper was to mostly make fun of some other papers (mainly by Hedges). While I agree that the science was bad in those papers and Graur and Martin were kind of funny in their paper, I felt it was also kind of unprofessional and I think there may have been a more diplomatic way to make it clear that the science was bad. I don't know, maybe that's just me. Science is supposed to be objective after all, not emotional.
Here are the main points:
-the findings summarized in a Trends in Genetics review are all based on a single calibration point and tenous methodology
-the calibration point is a supposedly well-constrained fossil divergence time between the ancestor of birds (diapsid reptiles) and mammals (synapsid reptiles) at precisely 310 ma
-the first problem is that this calibration has no errors associated with it. The second is Graur and Martin could not find the original reference to this calibration
-the authors suggest that a solution to the single-calibration conundrum would be to use multiple primary calibrations
-the use of standard errors as error bars in highly misleading, it is more appropriate to calculate the 95% or 99% confidence intervals
-the authors state that the appearance of these outlandish reviews have resulted in hundreds of citations in which such dates were accepted as factual, but they don't actually cite any. Was it really in the hundreds? I have my doubts.
Although this paper is mostly bashing another paper(s), it does get the point across that you have to be really careful with this methodology and not base your calibrations on someone else's calibrations. This paper is getting a bit old now and hopefully most researchers who work with divergence dating know this already and would never take calibrations from someone else's work. I mean, seriously. I do appreciate that the authors sate that molecular estimates of divergence times are useful when based on solid statistical methodology and multiple fossil calibrations. See, it's not all bad! :)