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."
