Sunday, March 05, 2006


Jurasic 'Beaver' - some musings to get your teeth into

This month's New Scientist reports on the discovery, in China, of a fossilized Jurasic 'beaver' (Castorocauda) about the size of a grey squirrel, which makes it the largest mammal-like animal ever found from the Jurasic period (i.e. 200-145 million years ago). Writing for New Scientist, Jeff Hecht says that the discovery 'reveals that earlier mammals were not only bigger than thought, but more diverse.' Moreover, according to Hecht, 'The discovery shows that fur, modern skin structures and warm-blooded metabolism originated very early in mammals.' Indeed, this fossil, from 164 million years ago, 'sports the oldest known fur.'

Now, the earlier and more diverse any given animal type (e.g. mammals) or feature (e.g. fur, modern skin structures, a warm-blooded metabolism) the more explanatory weight evolution by natural selection is being asked to carry. Evolution is clearly a fact of life, but equally clearly, one cannot demand that evolution explain more in less time indefinitely. Assuming that evolution is an adequate explanation for the appearance of x number of mammals/features in x amount of time, what about y (larger) number in x amount of time (or less time), etc? Now, I'm not saying that the assumption that evolution accounts for the arival of a 'more diverse' set of mammals/mammal-like animals & features in the required time frame is an instance when too much is being asked of evolution. As far as I'm concerned, it may or may not be. I'm just saying that the question should be addressed. But here is where our trouble starts. For the discovery of the Jurasic beaver surely raises the question of when the numbers become too much, of where the tipping-point between evolution being an adequate and an inadequate explanation comes. The denial that such a tipping point exists surely turns evolution from a scientific theory into a philosophical dogma unconcerned with empirical reality testing. Nevertheless, many scientists looking to explain the existence of mammals will simply assume a priori that evolution must be the explanation, rather than admitting a priori that 'it may or may not be' the explanation.

As an inset box in the New Scientist article says: 'Few fossils have been found of relatively large mammals living in the Jurasic, but it seems that these ancient mammals had already developed many of the traits the exist today.' The term 'developed', in context, clearly means 'evolved'. This is assumed rather than argued. Indeed, the fossil record itself clealry provides little or no support for this assumption. The fossils apparently do not show much gradual evolution from basic to more complex/modern mammals, but rather shows early Jurasic mammals with 'many of the traits that exist today'. Now, if one assumes that evolution is true then one will have to explain this fact away by saying that the fossil record is incomplete. These traits did evolve, but we have no material record of their evolution for some reason. This may be true; although the more digging we do, and the more fossils like our Jurasic beaver we turn up, the less likely such an evolutionary 'epicycle' becomes (and the more strained the evolutionary explanation becomes). At best this means admitting that the fossil record offers no direct empirical support for the assumption that these 'modern' traits evolved; and at worst it means that the fossil record is in tension with the predictions of Darwinian theory.

Finally, Hecht observes that our beaver 'has overlapping rib bones, a trait found among reptiles called cydonts that gave rise to mammals, but not in later mammals. The overlap is not found in the cydonts considered closest to mammals, so [Zhe-Xi] Lao thinks it re-evolved rather than being a holdover from its distant ancestors.'

Is this the re-expression of genetic information that had been superceded but had somehow lain dormant in cydonts who lost this physiological feature and then led (by whatever means) to mammals? Or is this another example of the 're-evolution' or 'parallel evolution' which some scholars, such as Simon Conway-Morris, think argues for teleology?

One thing is certain, discovering more fossils is not an activity which automatically supports the full-blown 'blind watchmaker' hypothesis.

<< Home

This page is powered by Blogger. Isn't yours?