Friday, January 21, 2005

Birds & dinosaurs: how science really works Science magazine has just published a summary of research on the developmental biology of dinosaurs and birds which not only confirms the evolutionary connection between the two groups of animals (basically, birds are dinosaurs of a particular kind), but that shows how real science (as opposed to, say, creationism?) works. Most paleontologists have agreed based on a variety of empirical evidence that birds are the direct descendants of a particular group of dinosaurs, but a consistent minority of scientists has disagreed (which, contrary to claims by supporters of pseudo-science, isn't a sign of crisis at all, but rather of a healthy critical debate among scientists). One of the "bones" of contention, so to speak, was represented by the development of fingers in birds and dinosaurs: both kinds of animals have three fingers as adults, as opposed to the five that are normal for vertebrates in general. Until now, however, scientists thought that while dinosaurs retained digits n. 1, 2 and 3, birds had lost n. 1 and retained the three middle digits. This would count as evidence against a close phylogenetic connection between the two groups. But new molecular developmental work has actually shown that what looks superficially like digit n. 2 in birds is really the standard first digit of vertebrates in general. Molecular biologists have been able to determine this by examining which genes are involved in the formation of the various digits in the developing bird embryo. Therefore, what seemed until recently an out of place piece of the puzzle turns out to fit perfectly with the prevailing hypothesis. This is the way science works: if new evidence supports the accepted hypothesis, the latter receives further confirmation and grows in strength and acceptance; if enough new pieces of evidence don't fit, eventually the hypothesis is discarded in favor of an alternative that explains things better. When was the last time you heard of an intelligent design proponent abandoning a hypothesis because it didn't fit the evidence? 9:50:18 AM    comment []