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Of Extinctions Great and Small

The theory of evolution troubled Victorians as much as it still troubles modern creationists. But even modern creationists fail to appreciate that the idea of extinction -- the disappearance, naturally or otherwise, of a species -- bothered Victorians as much as the idea of species mutability. We've come this far: We can still argue about evolution but nobody doubts extinction. Why? Extinction happens before our eyes. It can't be denied. It's commonplace. Ho-hum, another day, another couple of dozen extinctions. Our calluses are so thick that the word extinction no longer riles even the most strident creationist.

In fact, extinction is troubling in both fact and in theory. There is a lot to be said about it, but even with that said, extinction remains baffling. In No Turning Back Richard Ellis guides us along the many troublesome paths that radiate from the word extinction. His tour is interesting but resolves little. In the end, we are more perplexed than in the beginning, but such is the price science demands.

Ellis draws a distinction between macroextinction and microextinction. Macroextinction wipes out nearly everything in an instant while microextinction is that constant background, a slow process that takes out a species here and there and eventually gets everything. This background extinction is really perplexing but interesting mostly to specialists. The gene is very conservative and not prone to alter itself at a whim, yet environmental change is constant. Faced with environmental change, most species will not adapt, but follow their environmental niche to the grave. Nice bit of theory but it doesn't explain which species go next or why? Or why some species are so immutable while others are as mutable as putty. Or why this species seems to endure forever while that one is but a flash in the pan of time?

Macroextinction has captured the popular imagination mainly because dinosaurs have captured the popular imagination, and dinosaurs disappeared in a spectacular mass extinction. Not THE most spectacular but at least one of the top five or six. And not all the dinosaurs either, just most of them. You can look out the window and watch the surviving dinosaurs fly by.

The explanation for macroextinctions seems simple enough. If slow, constant environmental change leads to gradual extinctions, really fast environmental change must result in really rapid extinctions. The problem is that orthodox Darwinism resists catastrophes as an explanation for change so Darwinians have spent a lot of time trying to explain mass extinctions in terms of every day events. That's not been easy.

But what do we mean by routine change? Does a catastrophe last 10 million years, a million years, 100,000 years or is it a really bad afternoon? Recently, earth scientists have produced evidence associating macroextinctions with some pretty catastrophic events like Earth's collision with an asteroid of exceptional size. There, the problem is solved. It was a bad afternoon.

Well, nothing in science is that simple. To use the extinction of the dinosaurs as an example, it is clear Earth took a nasty hit around the time the dinosaurs disappeared. They might have disappeared that afternoon or say 300,000 years before that afternoon. There is a difference. Besides other bad things were happening about then, anyway. The planet was getting a lot colder, and there was a fury of volcanic activity. And a lot of things besides dinosaurs were going extinct about at the same time.

That's very satisfying. But in geological time about doesn't meanat the same time as. Did an asteroid shake up the planet enough to trigger volcanoes? Which came first? Were dinosaurs and other things going extinct at the same time and in response to the same factors or could the dinosaurs all have died of cold and diseases shortly before the asteroid struck? Why would alligators and crocodiles survive a cataclysm dinosaurs couldn't? The little, nocturnal, primitive mammals might have survived hidden in subterranean burrows hidden. That's a good hypothesis. But then explain why birds survived the same cataclysm while sitting in treetops.

All this takes up about a third of Ellis' book. The remainder concerns the sixth -- or present -- great extinction and deals with case studies of critters from the auroch to the wisent that have gone extinct in the last 15,000 years, are currently on the brink of extinction or have been pulled back, if only temporarily, from that brink.

There are two things that become apparent in these essays. First, the road to extinction is seldom straightforward and simple. Extinction seldom results from a single causative factor. Rather, several events and circumstances come together to lead to extinction. Likewise, rescuing something from extinction seems to require manipulation of more than one environmental factor.

Second, humans are at least partly to blame for almost all extinctions in the past 15,000 years or so and probably a batch of them, including some of our human ancestors, before that. We may pound the last of a species to death with a club, we may alter that all important niche space, or we may kill subtly by introducing our diseases or the diseases of our domestic animals. We don't have to use a gun to kill elephants. The tourists can just give them human tuberculosis. For nature, we are the new asteroid, the current catastrophe.

Ellis has produced a nicely illustrated, highly readable text on a complex, technical topic that is a current, hot topic in science or nature studies. This is the most recent in a series of exceptional nature/science books issued by HarperCollins and several of these have been reviewed in PopMatters (The Secret Lives of Lobsters, The Geese of Beaver Bog, and Becoming a Tiger.) We need to be reminded constantly that the planet's salvation is not entirely dependent on rapid economic growth.