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By blocking two genes that are activated when chicken embryos grow their beaks, U.S. researchers caused their jaws to 'revert' to a velociraptor-like or reptile-like snout. Credit: Bhart-Anjan Bhullar/Yale University. |
It's more bad news for the Creationism and the Intelligent Design industry, and this one is going to take a lot of explaining away.
Scientists have shown that inhibiting a couple of genes responsible for facial development in domestic hen embryos, causes the chick to grow a dinosaur face instead of a bird face. The authors also suggest their method could be used to investigate the mechanism of other major transitions in vertebrate history.
Abstract
The avian beak is a key evolutionary innovation whose flexibility has permitted birds to diversify into a range of disparate ecological niches. We approached the problem of the mechanism behind this innovation using an approach bridging paleontology, comparative anatomy, and experimental developmental biology. First we used fossil and extant data to show the beak is distinctive in consisting of fused premaxillae that are geometrically distinct from those of ancestral archosaurs. To elucidate underlying developmental mechanisms, we examined candidate gene expression domains in the embryonic face: the earlier frontonasal ectodermal zone (FEZ) and the later midfacial Wnt-responsive region, in birds and several reptiles. This permitted the identification of an autapomorphic median gene expression region in Aves. In order to test the mechanism, we used inhibitors of both pathways to replicate in chicken the ancestral amniote expression. Altering the FEZ altered later Wnt responsiveness to the ancestral pattern. Skeletal phenotypes from both types of experiments had premaxillae that clustered geometrically with ancestral fossil forms instead of beaked birds. The palatal region was also altered to a more ancestral phenotype. This is consistent with the fossil record and with the tight functional association of avian premaxillae and palate in forming a kinetic beak*.
*Copyright © 1999-2015 John Wiley & Sons, Inc. All Rights Reserved.
Blocking these two genes, which would normally cause the two premaxillary bones to fuse to form the beak, caused them to develop instead into a snout which looked much more like that seen in reptiles such as the avian sister clade, crocodiles, and in fossil velociraptors - which are believed to be the dinosaur ancestors of birds. It was also noticeable that the embryonic palate was also changed to look more like that of a dinosaur.
So it looks almost certain that this apparent major change in facial morphology as birds evolved from dinosaurs was due to just these two genes. For evolutionary biologists this is all perfectly rational and nothing more than we would expect to see.
As I pointed out in a blog just yesterday about another one of the 'non-existent' missing links that has just be discovered, because science is evidence-based and because evolution is such a basic fundamental of biological science, it is only to be expected that a new discovery dovetails perfectly into what we know already in broad terms. Almost all new discoveries simply add detail. If the difference between dinosaurs and birds turned out to be something that wasn't reflected in changes in genes, now that would be something really sensational. That really would require a major re-think and a major re-write of all the biology books, and several more besides. It isn't going to happen, of course.
But where does this fit in with any of the versions of creationism?
Maybe a creationist could help out here. Why would an intelligent designer design the mechanism for creating a dinosaur face in birds and then need to create two genes to switch it off and modify it to make a beak? Why not just design the means for growing a beak in the first place? Was it so scientists could one day switch off these genes and make the mistake of thinking this shows how dinosaurs evolved into birds, just to deceive us, maybe?
Of course, what creationists really need to explain is just why all the evidence and all the new discoveries made by the relevant sciences invariably support evolution by descent with modification and never support any of the different versions of creationism.
Alas, about the best we can expect will be more infantile abuse, attacking straw men, evidence-free assertions and Bible/Qur'an verses.
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