« Coevolution and gene flow | Main | Rock-paper-scissors for high stakes »

Scientific controversy: dinosaur-tail soup ?

This week I want to talk about scientific controversies. In politics or religion, any difference of opinion may qualify as a controversy, which some may try to "settle" by killing those with opposing views. Most scientists would agree that unsupported opinion isn't enough to make a scientific controversy. A scientific question is controversial only if people are actually publishing data that seem to lead to different conclusions.

Two papers in press in Proceedings of the Royal Society illustrate current scientific controversies. The first is "A new Chinese specimen indicates that 'protofeathers' in the Early Cretaceous theropod dinosaur Sinosauropteryx are degraded collagen fibers" by Theagarten Lingham-Soliar (linghamst@ukzn.ac.za) and colleagues at the Universities of KwaZulu-Natal and North Carolina and the Chinese Academy of Sciences.

The title pretty much says it all. (Collagen is what gives shark-fin soup its distinctive texture, hence the title of this entry.) If the conclusions in this paper become generally accepted, how would that change our overall understanding of evolution?

The two elements of evolutionary theory that upset creationists most wouldn't be affected at all, of course. Our confidence that the universe is a million times older than Bible-based estimates, and that humans and chimps share a recent common ancestor, is based on multiple lines of evidence for each, none of it dependent on which dinosaurs had feathers, if any.

But what about the claim that birds are descended from dinosaurs? Let's see what a leading textbook, "Evolutionary Analysis", says. Page 44: Sinosauropteryx had what "some paleontologists believe are primitive feathers." Page 45: they cite several papers, one questioning this conclusion. "More convincing are [true feathers on] the dromesaur fossils." Page 553: "Luis Chiappe (1995) used skeletal characters to infer the phylogeny [family tree] of early bird lineages." The tree shown has protofeathers near the base, followed by true feathers. If the P. Roy. Soc. paper is correct, that would only require revising the earliest branches of his tree.

So this is a real controversy, but it's only a controversy about where feathers appeared in the family tree of dinosaurs and birds. As the paper says, "the wider question of whether or not birds originate from dinosaurs does not concern the present study." The main fossil evidence that they did comes from analysis of skeletons, not feathers. We don't have DNA from dinosaurs, but genetic comparisons among living species suggest that birds are more closely related to crocodiles than to mammals (Science 283:998). So birds-from-dinosaurs still seems likely.

The second paper is "Context dependence in the coevolution of plant and rhizobial mutualists" by Katy Heath (heat0059@umn.edu) and Peter TIffin, whose lab is next to mine. Among other things, this paper shows that plants infected by two different strains of rhizobium bacteria often grew less than those infected only with the worst of the two strains. This result may become controversial soon, when Toby Kiers and I publish data apparently showing that plants infected by two different strains can grow more than those infected with only the best strain. Our experiments were done with soybean, whereas theirs used a wild relative of alfalfa, which houses rhizobia in a different type of root nodule (see photos). Also, our two strains were much more different than theirs. So maybe this doesn't really qualify as a controversy, at least not yet.



Nodule photos taken in our lab (c) Inga Spence... licensing from www.alamy.com.

When there is a controversy, should it be taught? We certainly shouldn't teach a conclusion as certain when it is still (genuinely) controversial. And students should learn about some past scientific controversies, to understand how they were resolved. The triumph of evolution would be a good example. Exposure to some current controversies would be good, too, assuming teachers have time to keep up with the literature, well enough to know what has been settled (at least until convincing new data to the contrary are published) and what is still controversial. I remember Professor Spanswick, at Cornell. telling us "I found the evidence for the chemiosmotic hypothesis convincing, but always presented it as a controversy... until Mitchell won the Nobel Prize for it."


Thanks, Ford. Although I am not a scientist, I find your articles interesting and often illuminating. I also appreciate your asides. ADL

Thanks, Aunt Ann. You are my target audience (intelligent, curious, nonspecialists), so any suggestions on clarity etc. would be appreciated.
"A supercomputer? My aunt had one." -- Woody Allen

Let me add my thanks for your efforts since I guess that I fall in your target audience too. I've only a high school education, (and that fifty years ago), but your articles generally ring clear as a bell to me. I especially enjoyed the dinosaur/bird info since it reminded me that it was my hero, T. H. Huxley, who first claimed, in about 1868, that birds had descended from dinosaurs. Anyway, thanks for taking the trouble to do these articles.

Bulldogs may not travel as much as beagles, but you can still learn a lot from them!

:) I like that. I learned a lot from the Huxley biography by Adrian Desmond, (1994), and even more from the trove of Darwin letters recently put online.

I question how legitimate the dino-feathers "controversy" really is. It seems to me that the people promoting the collagen view show all the classic signs of being cranks. Their quotes in this National Geographic article about how everyone else's science is "faith based", and how they're being persecuted by the majority view, sound like they could have come from the Discovery Institute:


From what I can tell, they're study was deeply flawed, and they are grossly overstating their findings, also tell-tale signs of crank science.

If the dubious collagen hypothesis and the whining about being persecuted are all they have to support their view, then I'm inclined to say that there is little or no controversy at all.

If you can get access to the paper, have a look at the photos and see what you think. I found them reasonably convincing, but I'm no expert. I agree that whining is usually a sign of junk science, though. Either way, refuting protofeathers on these dinosaurs says nothing about true feathers on other dinosaurs -- Wikipedia lists 15 feathered dinosaur genera -- or the evolution of birds from dinosaurs.

See also these related stories from other blogs:

Post a comment

(If you haven't left a comment here before, you may need to be approved by the site owner before your comment will appear. Until then, it won't appear on the entry. Thanks for waiting.)

Type the characters you see in the picture above.