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Tuesday, October 21, 2008

Method used determines which evolution story is told

Genetic sequence comparisons are used to try to establish relationships in evolution. But as Robert Deyes, writing over at Access Research Network, shows, the molecular "clock" can conflict wildly with the traditional "tree of life":
Writing over a decade ago, UCLA biologists Laura Maley and Charles Marshall noted how genetic sequence comparisons carried out between different animal phyletic groups can lead to significantly different interpretations of evolutionary relationships depending on which species is chosen to represent each group (Ref 1). Such a finding should raise concern amongst protagonists of molecular systematics who today use sequence data to determine evolutionary relationships. Yale University's Gavin Naylor showed just how inaccurate such comparisons could be in the context of the vertebrate evolutionary tree (Ref 2). Mitochondrial DNA sequence analyses of 19 different taxa generated an astounding result- frogs and fish were clustered in the same clade as chickens even though "strong morphological and fossil evidence" did not show these as being in any way related by a common ancestor (Ref 2). The same mitochondrial DNA sequences placed echinoderms- which include starfish and sea urchins- in closer proximity to the vertebrates than amphioxus even though, being a chordate, we would expect amphioxus to be closer (Ref 2). That is, if we give the evolutionary tree any credibility.

Given such anomalies, one should be cautious about stating what we really do know about the evolutionary relationships between different classes of vertebrates. Nevertheless molecular biologist Thomas Sakmar and his colleagues from the Rockefeller University seemingly threw caution to the wind several years later when they redesigned the rhodopsin molecule- a visual, light perceiving pigment that is ubiquitous throughout nature (Ref 3).

Find out why there is an intelligent design controversy:

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