Tuesday, March 23, 2010

Evolution, Extinction, Catastrophe

Gary Tedman

I am sure it is not my imagination, and that we are constantly asked to believe two opposing things about prehistoric change: 1) that dinosaurs became extinct due to an asteroid smashing into the Earth (10-15km space rock striking the Yucatan Peninsula),

[see http://news.bbc.co.uk/2/hi/science/nature/8580444.stm]

and 2) that birds are the modern descendants of dinosaurs (the therapods). Both cannot be true, but while the latter thesis is the more scientific, it is the former big catastrophe that gets most of the media attention.

Just recently a report came out on the BBC of a theory about how another earlier big extinction event, the end-Triassic, involving massive volcanic activity and lava flows, may have helped the rise of the dinosaurs in their evolution over their main competitors the crurotarsans (like crocodiles).

The details remain obscure how this could have happened, but it occurred to me how the two kind of events might be considered quite similar as catastrophes go, and so it is rather strange that they produce opposite effects for the dinosaurs. But I would not press the point (the forcing effects on global climate are complex in both cases, and clearly can be different).

However, it does seem to me that there is a large amount of sensationalism and of covering up of evolution happening in these kind of reports. We would be inclined to think from these stories that the main mechanism of natural history was violent and sudden disaster and had nothing to do with the slow and incremental processes of evolution.

But consider this: big extinction events are likely to be harmful to a broad range of creatures on the planet, not just a specific type or genus. And even a specific effect upon one species will impact inevitably on others in the ecosystem, because of the way they are connected in the 'food chain'. Therefore I think it is likely that these big events, while they certainly destroy life, it is still evolution itself that is the motor of the development of species.

The fact that a certain species cannot survive an environmental catastrophe as well as another species is the point I am making here. Dinosaurs did survive the asteroid impact and so did mammals, but at least up to now we can see that mammals, after this stage, gained a bigger foothold on the planet. The reason for this is evolution, and I suspect that in the circumstances mammals survived better because of their method of birthing and looking after their young more caringly (a necessity without external egg laying). That those dinosaurs evolved and survived which led to birds, which lay their eggs in relatively inaccessible (to mammals?) locations seems to me to be obvious and present evidence of a tendency towards an environment where the predation on ground laying eggs became unsustainable due to predation or other environmental factors, and a relatively new environment in which the birth strategies of mammals proved more effective.

The same or similar factors could be true in catastrophes that enabled the opposite, the rise of the dinosaurs to greater prominence. Often in evolution too much success can be as bad as too little, the dominant species can get too 'comfortable' and fixed in its environmental niche where it is successful, and when a sudden disaster occurs that changes this environment on a dramatic scale, it has no capacity to change quickly enough from its usual ways. Therefore it dies on a large scale. This creates or leaves a space for other species, formerly not so well suited to the existing conditions, to move in. It is therefore not just a question of the 'fittest' because the fittest, here, fails, and the weak veritably 'inherit the Earth'.

There is a message in this for the human species, somewhere.