Chance, Competition, and Catastrophe

The arguments above and the examples offered below can be heuristically thought of as chance, competition and catastrophe. All of these terms emphasize the historical contingencies that lie at the heart of the evolution of species. A change in a species is the result of an unpredictable series of antecedent events, and not “predictable outcomes from laws of nature.” Change in living species is constrained by all preceding events; changes are limited by the genetic materials at hand, bequeathed to the organism by past generations. Differential reproductive success and mutation are the raw materials of morphological change, but the former is notoriously dependent on local, changing conditions and the overwhelming majority of mutations are deleterious. If a novel adaptation is sufficiently advantageous (for example, bipedalism in the hominid lineage), the resulting changes are by no means necessarily the “best solutions.” Natural selection can operate only on the status quo. As a result, most changes in species are jury-rigged solutions, cobbled together by a tinkerer - certainly not what one would expect from a cosmic watchmaker. If we could be objective about ourselves, we would admit that there are much better body plans, and that any sophomore at Cal Tech could design a human body plan with far better engineering solutions to the pains and failures brought on by bipedalism (from hernias to backaches to dysfunctional feet and the difficulties of childbirth), not to mention equally inept “solutions” in the visual and vascular systems.

Evidence has surfaced in recent years that widespread catastrophes were more important in earth’s history than previously thought. Sometimes a planet-wide event scours the earth of nearly all life. The great granddaddy of these mass extinctions occurred in the Permian (245 million years ago), and caused the extinction of 96% of all creatures on earth. The later Cambrian decimation, which eliminated 80 - 90% of the panoply of wonderful new creatures that had evolved, whose remains are richly preserved in the Burgess Shale, has been eloquently described in Stephen Jay Gould’s book Wonderful Life. In that volume Gould says that one purpose of his book is to make a statement about the nature of history and the awesome improbability of human evolution.

A mass extinction that has deservedly caught the popular imagination occurred at the end of the Cretaceous, when an interplanetary object smashed into the earth, and incidentally did the mammals a great favor; it eliminated all the dinosaurs. For a hundred million years dinosaurs dominated the planet: the land, the sea, and the air. (By contrast our hominid lineage has been around for only about 7% of that time.) And, despite their opportunities over this hundred million years, and the astonishing variety of forms that appeared, there is no evidence that dinosaurs showed any trend towards higher intelligence.

Had it not been for cosmic intervention, the small shrew- or vole-like mammals scurrying around between the dinosaurs’ legs - picking up crumbs, so to speak, from the dinosaurs’ table - would probably be about the same insignificant mammals today. It would seem that the unprepossessing early mammals could not successfully compete with the dinosaurs. But when a fortuitous event eliminated the dinosaurs, the myriad of new opportunities in the environment resulted in an explosive radiation of the mammalian species.

Beyond the kinds of catastrophes mentioned above, there have been many other major changes in earth’s ecology. We are only beginning to understand the consequences of alternating tilts in the earth’s axis, or the consequences when the magnetic poles reverse. We are also in a very early stage of understanding long-range weather patterns, but the geological record has already revealed that some major ecological changes can take place in less than a century, and some can be measured in decades. Note that a species that is most able to survive and take advantage of the opportunities following a catastrophe is often able to do so because it adventitiously had traits that, while not especially remarkable during the long period leading up to the catastrophe, were suddenly very advantageous.

Contributed by: Dr. Irven DeVore