Jonathan Wells on the contemporary state of Evo-Devo
|April 2, 2007||Posted by William Dembski under Evolution, Biology, Darwinism|
I asked Jonathan Wells to put together the following brief update on evo-devo.
A March 30 press release from the University of Bath quoted evolutionary biologist Ronald A. Jenner as saying: Ã¢â‚¬Å“Since its inception, some workers feel that evo-devo hasnÃ¢â‚¬â„¢t quite lived up to its early expectations.Ã¢â‚¬Â
This is an understatement, since evo-devo has not provided an experimentally confirmed explanation of even a single case of macroevolutionary change. Yet JennerÃ¢â‚¬â„¢s sober assessment contrasts sharply with the extravagant boasting of Darwinist Sean B. Carroll: Ã¢â‚¬Å“Evo Devo reveals that macroevolution is the product of microevolution writ large… We now have a very firm grasp of how development is controlled. We can explain how tool kit proteins shape form, that tool kit genes are shared by all animals, and that differences in form arise from changing the way they are used.Ã¢â‚¬Â (Endless Forms Most Beautiful: The New Science of Evo Devo, Norton 2005, pp. 291, 295)
Maybe Jenner and Carroll should talk…
Most research in animal development focuses on six model systems: fruit flies, roundworms, frogs, zebrafish, chicks and mice. According to the Bath press release, Jenner doesnÃ¢â‚¬â„¢t think these are enough: Ã¢â‚¬Å“Whilst this is generally fine in the context of development research, the benefits to evo-devo as a subject are limitedÃ¢â‚¬Â¦ Instead, we urge workers to select new models specifically to illuminate hitherto neglected general themes within evo-devo.Ã¢â‚¬Â JennerÃ¢â‚¬â„¢s co-worker, evolutionary biologist Matthew A. Wills, agrees: Ã¢â‚¬Å“Establishing criteria for choosing model organisms is important in this field, especially given the pressure on available funding sources. We encourage evo-devo workers to communicate with funding agents so that the limited resources available will not be disproportionately channelled to the Ã¢â‚¬Ëœbig six,Ã¢â‚¬â„¢ which, while important, cannot illuminate all evo-devoÃ¢â‚¬â„¢s central themes.Ã¢â‚¬Â
It is clear from statements by Jenner and Wills that Ã¢â‚¬â€œ like other Darwinists Ã¢â‚¬â€œ they assume that all animals are descended from a common ancestor. Yet the very focus on a few models systems that they decry has discredited evidence for this assumption.
Darwinists have been telling us for years that some of the best evidence for the common ancestry of insects and vertebrates is their Hox genes, which affect the character of body segments during embryo development. For example, a mutation in one Hox gene can cause a fruit fly to sprout a leg from its head in place of an antenna. Remarkably, vertebrates possess Hox genes that are very similar to a fruit flyÃ¢â‚¬â„¢s Ã‚Â¬Ã¢â‚¬â€œ so similar that a mouse Hox gene can enable normal development in a fly embryo that lacks its corresponding Hox gene. More remarkably, the order in which Hox genes are lined up on the chromosome is the same as the order in which theyÃ¢â‚¬â„¢re expressed along the embryoÃ¢â‚¬â„¢s body axis Ã¢â‚¬â€œÃ‚Â¬ a feature known as colinearity. And most remarkably, colinearity is the same in the four Hox gene complexes of vertebrates as it is in the Hox gene complex of the fruit fly Drosophila melanogaster.
This striking similarity in Hox gene colinearity is often cited as evidence for common ancestry. For example, according to a widely used college textbook, Ã¢â‚¬Å“The ordering of the genes within each vertebrate Hox complex is essentially the same as in the insect Hox complex, suggesting that all four vertebrate complexes originated by duplications of a single primordial complex and have preserved its basic organization.Ã¢â‚¬Â (Bruce Alberts et al., Molecular Biology of the Cell, Fourth Edition, Garland Science 2002, p. 1194)
Last year, however, seven different arrangements of Hox genes were reported in various species of Drosophila Ã¢â‚¬â€œ all fruit flies, in only one of the six model systems mentioned by Jenner and Wills. Apparently, the arrangement in Drosophila melanogaster that so strikingly resembles the arrangement in vertebrates has not been inherited from a common ancestor but is a relatively recent acquisition. (B. Negre and A. Ruiz, Ã¢â‚¬Å“HOM-C evolution in Drosophila: Is there need for Hox gene clustering?Ã¢â‚¬Â Trends in Genetics 2006, doi:10.1016/j.tig.2006.12.001)
So this showcase piece of evidence for the common ancestry of animals Ã¢â‚¬â€œ one of Ã¢â‚¬Å“evo-devoÃ¢â‚¬â„¢s central themesÃ¢â‚¬Â Ã¢â‚¬â€œ turns out to be false, disproved by analysis of only one of the Ã¢â‚¬Å“big sixÃ¢â‚¬Â model systems.
I guess if I were a Darwinist I would want funding to look at other systems, too.
Jonathan Wells, Ph.D.