A new fossil discovery has hit the press, as reported in Science online and many other places, a 150 million year old HO-gauge Tyrannosaurus rex. This 'small' (human size) creature looks so much like the famous Hollywood star (and actual fossil), that it has caught paleontologists by surprise. It is making good news fodder (and will surely be the basis of a Hollywood sequel).
The new find from northeastern China, named Raptorex kriegsteini, is about 35 Myr older than the famous movie star that draws countless tourists to natural history museums, and much much smaller, perhaps 150 pounds, but with the same short arms, large head and jaw, and long tail. The prevailing theory of the selective forces that molded the giant version of this animal, the big-tailed, huge-thighed, tiny armed, upright vicious predator was that to be as big as an American car they had to have this shape.
The powerful carnivore, so the story went, evolved from a very different ancestor, developing its oddities because it became so large. It needed a large head, powerful jaws and sharp teeth to capture its prey, and strong legs for running, but, it was said, with long forelimbs, it would have been top-heavy and its running ability hampered, so its arms shrank into the short limbs we all readily identify with T. rex.
Paleontologists can discuss the morphological aspects of this fossil in a meaningful way that we can't, but the relevant issue for us, and this blog, is the nature of explanations in evolutionary science, and the confidence with which we tend to hawk them to the public and, probably worse, to ourselves.
Clearly, this new miniature replica shows that the original explanation was overstated if not completely wrong. It may be that the same shape considerations would have worked on a smaller scale, if T. wrecks was subsisting in such a relatively minaturized environment, in the way that toy trains work just like real trains, but on small tracks. But what would the proof of that small-scale argument be, given the clearly false original argument?
It is easier to reconstruct evolutionary history than evolutionary scenarios. The former describes the temporal biogeography of past life, based on actual evidence. Incomplete though it be, the evidence is at least a partial picture of things from the actual past. The problem of reconstructing evolutionary scenarios is that here we are trying to bring specific processes and events back to life. They can't be observed directly.
It is perfectly natural for us to try to explain form in terms of our ideas about process, and of course this is done in a (usually rigid) Darwinian way, in terms of the selective forces that 'must' have been operating. But when one new find can undermine or overturn such scenarios, how confident can we be in the ones that haven't been overturned (yet)?
The same comments probably apply widely in paleontology, even to species so utterly boring or remote that they have no cinematic interest. It certainly has been a plague in anthropology, where finds like a new finger-bone are touted as revolutionizing our understand of human evolution. When one new knuckle can do that, we should knuckle down and keep our interpretations well within the sanity zone, but that seems difficult to do, given the hunger of the media (as well as attention-hungry scientific journals like Nature).
It's for reasons like these that evolutionary biology has long, and often rightly, been accused of conjuring up "Just-so" stories, the phrase from Rudyard Kipling's children's tales. We explain our empirical findings with stories of processes and events that we are inventing, or guessing at. What we are actually saying is not what did happen, but that what we see appears as if such-and-such was going on. In turn, that provides plenty of fodder for those who use our tall tales to argue that, to the contrary, evolution didn't happen at all.
Making up stories and calling it Science is only good at the box office. While we can and should try to guesstimate the way life was in the past, we need to be a lot more modest in doing so. How many times does a T.rex have to be ruined by a T.wrecks before that lesson is learned? Or when will funders penalize over-zealous claims, to bring science back into a less hubristic mode of operation?
Probably, this won't happen as long as there are television, movies, authors, and journals who have something to sell. And that's our "Will-be-so" story of the day.