Thursday, July 5, 2007

A Personal View of Evolution

I am both a believing Christian and a practicing scientist. I believe that the Bible provides insight into the most difficult questions that face humanity, that it treads fearlessly where science will forever be reticent, that it is a product of thousands of years of thinking by some of the best minds in theology. Yet I am also a biologist and an advocate of evolution. I think that evolution has extraordinary power to explain seemingly-unrelated observations, that it may be the finest and strongest and best example of what science strives to be, that it is the product of more than a century of thinking by some of the best minds in science.

Evolution is a gradual process of change; to a biologist this change relies on simple precepts:

1) Variation exists. Any large gathering of people will include some who are old and some who are young, some who are weak and some who are strong. It could be argued that most such variation is meaningless in an evolutionary sense, and this may well be true. But variation exists in all organisms of all species in all places.

2) Some variants are more successful than others. Imagine a herd of antelope, in which some are old and some are young, some are weak and some are strong. Clearly, if a lion were stalking that herd, the old or the weak would be more likely to suffer predation. Predation is not random; lions risk injury every time they hunt, so they seek the weakest prey. Even then, lions are not always successful; sometimes they are unable to kill their prey. Nevertheless, there is a stronger selection pressure against the weak than against the strong.

3) Variation is heritable. Everything we know about our own families convinces us that certain traits are likely to run in families; tall parents tend to have tall children, just as near-sighted parents tend to have near-sighted children. Everything we know about genetics concurs that certain traits are passed down to offspring, often with a high degree of fidelity.

4) Successful variants tend to become more abundant over time. Because certain individuals are more likely to survive long enough to reproduce, and because those individuals are able to pass specific traits on to their offspring, those traits are well-represented in future generations. In contrast, other individuals may have traits that lead to premature death, so these traits are less likely to be passed along. Over time, successful traits will tend to increase in a population, whereas unsuccessful traits will gradually be lost.

The “inventiveness” of evolution emerges from a combination of processes that would seem to be polar opposites; a random process of change or mutation, and a non-random process of assessing that change, in the harshest possible fashion. Though mutation is indeed a random process, mutations are subject to natural selection, which is far from a random process.

Mutation generates few changes that are ultimately successful, just as a blind watchmaker would rarely be able to alter a watch to make it more accurate. We would not accept repairs by a blind watchmaker without testing whether the watch still works. Similarly, random changes to an antelope are subjected to the stringent selection pressure of a hungry lion. Thus, the process of natural selection removes unsuccessful mutations from the gene pool in the most unforgiving way imaginable. The lame, the halt, the weak, and the poorly-adapted; all are killed with an egalitarianism that is inexorable. Evolution is not a random process at all.

Among scientists, the details of evolution are subject to argument, but it is not controversial in any larger sense. It is essentially impossible to be a biologist without accepting the tenets of evolution, just as it is impossible to be an astronomer without accepting gravity. It is not that evolution is a belief system; evolution is an incredibly elegant, simple, powerful, direct, testable, and compelling set of ideas. Evolution is a “theory” in the same sense that gravitation is a “theory”; there are aspects of gravitation that are still not well understood, but we won’t fly off into space while we argue the details.

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