Friday, November 17, 2006

World: Evolution is not steady

Many people think of evolution as a steady upward process. The phrase “survival of the fittest” is rooted in our collective consciousness, and we imagine a constant winnowing on that basis. Everything that has gone before and extinguished must, ipso facto, be inferior on the evolutionary scale.

Two – linked – concepts mitigate against this: cataclysm, and punctuated equilibrium.

Mark Maddison explained to me punctuated equilibrium, whereupon I promptly suggested punctuated evolution would be more accurate. Little did I know about the equilibrium part of the equation.

Developed by Niles Eldredge and Stephen Jay Gould, Punctuated Equilibrium postulates that evolution happens largely in discrete bursts, separated by long periods of relatively little change. This accords in general with geological records – which Darwin noted, but ascribed to the incompleteness of research.

It’s rather at odds with the popular understanding of evolution as a battle for superiority that constantly forces change. It suggests ecosystems (local or global) on the whole tend more towards stability than antagonistic competition. [however, I would note that it describes evolution as happening rapidly at points of punctuation, but is less vocal on the rate of change at equilibrium - for example, to distinguish between stasis and slow change.]

Punctuated equilibrium still strikes me as somewhat counterintuitive. But it's easy to appreciate the role of cataclysm in the course of evolution. It’s generally accepted – and fairly widely understood – that the era of the dinosaurs came to an end when a meteor hit Yucatan (Mexico). It was more or less 10 kms wide, and caused mass extinction of many species.

This is an example of survival – and evolution – being due to a very specific event that is not intrinsic to the terrestrial environment. In effect, there could well have been species on a superior evolutionary path, but which simply couldn’t survive a given cataclysm. Note that ‘superior evolutionary path’ does not equate to ‘more evolved’. All we can say is we are, of course, the most evolved of species to date: the simple proof is that only significant human artifacts remain in the geological record. But who’s to say those extinguished species wouldn’t otherwise have evolved further or faster than us in the absence of cataclysm?

Thus singular events have wiped out a number of evolutionary paths, and one could say that we’re here by circumstance – last one standing – rather than being the undisputed peak of all prior evolutionary paths.

Still, we can take comfort that no species has evolved on earth further than us.

These thoughts are encouraging: the earth has weathered catastrophe in the past (and despite what I envisioned when younger, we don’t even have the ability to blow the planet apart). So whatever we do, life on this planet is likely to continue until the sun is dying. Puts it all into perspective.

I expect that many people - not just the strongly religious - would find this hard to accept because it’s insufficiently anthropocentric.

1 comment:

Bazza said...

Really, really interesting post, Stephen, and an absolutely fascinating subject. I don't think that the concept of punctuated equilibrium in any way detracts from the solid sense of evolutionary theory but it does explain how one of the things creationists keep bringing up is explained; namely long periods with no fossil evidence. If there is a burst of evolutionary change over a relatively short period the fossil record could easily be lost.