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
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