Featured topic 12/08: Your Favorite Evidence

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My apologies for being kind of late with this month’s post.  I was going to post it earlier, but didn’t think I should yet because Christian Forums was down, and this topic involves linking to a thread there.

Anyone who consistently debates with a particular group of people is likely to have certain arguments against the opposing position which they’re particularly fond of.  It could be because these points are particularly striking, particularly difficult to refute, or for any other reason.  This trend isn’t restricted to creationism vs. evolution—I’ve noticed the same thing in some of the debates that Jason Malloy of Gene Expression has with people who insist that there are no biological differences between humanity’s races.  (For more details about that topic, see our post from October.)  So this month’s topic is: What is your favorite line of evidence for evolution, and why?

In my case there are two answers, for two different reasons.  The first answer is endogenous retroviruses, and in particular this essay about them.  For those who don’t know, endogenous retroviruses are bits of DNA that are inserted into an organism’s genome as a result of a failed viral infection, which can in some cases be passed on to its offspring.  No two ERVs are the same, even if they came from the same virus, since what specific bits of DNA are left behind and where in the genome they’re left is different for each infection.  So if two animals share an ERV, there is no plausible explanation for this except that they both inherited it from a common ancestor.

As the aforementioned essay shows, the pattern of ERVs found in humans and other primates exactly mirrors the relationships between them which has been concluded from fossil and anatomical evidence.  This essay also does an excellent job refuting basically all of the creationist arguments against this idea.  My fondness of this essay in particular relates to a second reason why I especially like this line of evidence—this essay was written by R. Allan Glenn, who was a friend of mine in my debates with creationists in 2004 and 2005, but died in November of 2005 from complications of cystic fibrosis.  A lot of members of the creation/evolution section at Christian Forums still regard Allan’s essays as so authoritative, they continue to cite what he’s written there even three years after his death.  Many of them, myself included, consider his essay about endogenous retroviruses to be among his best.

A second piece of evidence that I particularly like relates to evolution’s ability to predict future discoveries; something which creationism has never been able to match.  One of the best examples of this is the fact that several paleontologists were able to predict the existence of feathered dinosaurs more than a decade before they were discovered.  (Perhaps "predict: isn’t the best word to use here, since the feathered dinosaurs obviously existed already, but the point is that the theory of evolution was able to determine their existence before there was any direct evidence for it.)

The paleontologist who’s most famous for having made this prediction is Gregory S. Paul, whose book Predatory Dinosaurs of the World contains several illustrations of the plumage he’d concluded these animals would have had.  One such illustration can be found here.  As can be seen from the date on this drawing, it was created in 1988, while the first feathered dinosaur fossil to be discovered, Sinosauropteryx prima, wasn’t found until 1996.  Greg Paul also managed to correctly predict a few more specific details of their anatomy, such as the fringes or "proto-wings" on the Velociraptor’s arm, which have more recently been discovered in the fossils of dinosaurs such as Caudipteryx and Sinornithosaurus.

The prediction about feathered dinosaurs that I consider most striking, though, was not nearly so recent as the 1980s.  In 1915, the American zoologist William Beebe reached a conclusion about the type of animal from which birds would have evolved, based on his studies of bird embryos.  He predicted that their ancestors would have included a small, feathered dinosaur that flew using wings on its legs as well as its arms—a fairly good description of Microraptor gui, a feathered dinosaur whose remains were discovered 88 years later.

William Beebe also illustrated this hypothetical animal, which he referred to as “Tetrapteryx”.  To anyone who does not know this illustration was created in 1915, it could easily be mistaken for a reconstruction created within the past five years of 2003’s discovery.  I’ve included his illustration side-by-side with the original fossil in order to show their similarity; note the unique “leg-wings” in each case.



In addition to my general interest in feathered dinosaurs, the reason why I particularly like this piece of evidence is because it’s one of the only examples where it’s possible to show an illustration, based only on an understanding of evolutionary theory, of something whose existence was not actually discovered until decades later.  What other specific pieces of evidence for evolution are the people here especially fond of, and why?

—Agahnim