Posted on 10/08/2009 2:40:05 AM PDT by chuck_the_tv_out
Nature has recently published an interesting paper which places severe limits on Darwinian evolution. The manuscript, from the laboratory of Joseph Thornton at the University of Oregon, is titled, “An epistatic ratchet constrains the direction of glucocorticoid receptor evolution.” The work is interpreted by its authors within a standard Darwinian framework, but the results line up very well with arguments I made in The Edge of Evolution. This is the second of several posts discussing it.
Using clever synthetic and analytical techniques, Bridgham et al (2009) show that the more recent hormone receptor protein that they synthesized, a GR-like protein, can’t easily revert to the ancestral structure and activity of an MR-like protein because its structure has been adjusted by selection to its present evolutionary task, and multiple amino acid changes would be needed to switch it back. That is a very general, extremely important point that deserves much more emphasis. In all cases - not just this one - natural selection is expected to hone a protein to suit its current activity, not to suit some future, alternate function. And that is a very strong reason why we should not expect a protein performing one function in a cell to easily be able to evolve another, different function by Darwinian means. In fact, the great work of Bridgham et al (2009) shows that it may not be do-able for Darwinian processes even to produce a protein performing a function very similar to that of a homologous protein.
Before reading their paper, even I would have happily conceded for the sake of argument that random mutation plus selection could convert an MR-like protein to a GR-like protein and back again, as many times as necessary. Now,
(Excerpt) Read more at evolutionnews.org ...
Evolution almost sounds... engineered!
” “An epistatic ratchet constrains the direction of glucocorticoid receptor evolution.” “
...
That’s all very well, but what are we going to do about the Eye-talian?
How did reproduction “evolve”?
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