REPTILIAN TOOTHED JAWS AND BIRD BEAKS HAVE AN EVOLUTIONARY HISTORY

A recent study by Yale scientists used molecular tools to reconstruct the shift from reptile-like snouts to bird beaks.  The scientists first did a thorough comparative anatomy of the mouths of birds, turtles, crocodiles, and lizards and compared those to the bone formation in the mouths of fossil birds and reptiles. They then studied the embryos of chickens, emus, turtles, and crocodiles to identify when the genes for jaw or beak formation took place.  They cloned the DNA from these active genes and used repressor molecules to turn off the genes involved in beak formation of chickens.  This led to the expression of silent genes that were still present in birds.  The major changes involved the shape and state (fused or unfused) of the palatine bone in the roof the mouth and the premaxillary bones.  It also involved the presence or absence of teeth.  Identifying the genes involved in repressing tooth formation and in determining which bones fuse and how the bones are shaped reveals how close the inferred evolutionary sequence of events resemble the experimentally induced sequence of events that can be manipulated with a knowledge of the genes involved.  This was not a sci-fi attempt to produce dinosaurs from birds and cognate animals.  It was an attempt to see how at a molecular level, the events occurred in shaping the jaw or beak and how remnants of those lost processes found in reptiles still exist in the genomes of birds. I enjoyed reading the accounts of the Yale group because it reinforces the importance of experimental science to test predictions and to reveal new knowledge. It reinforces the importance of reductionism in science.  The whole cannot be understood without an attempt to identify the components of complex systems. Without probing, comparing, studying, and using experimental manipulation, complex systems are mysterious and invite supernatural or superficial interpretations. I would not be surprised that a search for genes for tail formation would be found in humans.  It makes me aware that every species is unique in its expressed genes and in its hidden, suppressed (or deleted), genes found in cognate species.  We are genetic palimpsests of our past ancestors. The history of science reveals the piece by piece way theories evolve.  The search for our ancestors using census and birth records or genealogical repositories shows us  branches of our family we did not know existed.  The study of languages show how they evolved and the older the literature, the more difficult it is for us to read it as we go from Victorian prose to Shakespeare to Chaucer and to Beowulf.  Everything changes and scholars can use reason to reconstruct the changes that lead to the present.