A conservation with George C. Williams

"I am convinced that it is the light and the way." These are the final words in Adaptation and Natural Selection, George C. Williams's 1966 book about evolution. In the decades since the publication of this book, which became one of the most influential in its field, nothing has altered Williams's conviction that evolutionary theory is not just of it intellectual interest but has much practical significance for human life.

A marine biologist by training, Williams took two sabbaticals to conduct fish research in Iceland, but he is most widely known as a theoretician. As early as 1957, he wrote a paper on senescence considered by some to be a cornerstone of modern evolutionary theory. Williams has also written passionately about the "moral unacceptability of natural selection" and the necessity Of using our intelligence to triumph over it. For a paper on evolutionary ethics, Williams came up with one of the most eye-catching titles in scientific literature: "Mother Nature Is a Wicked Old Witch."

Despite his strongly held convictions, Williams says that for him, controversy is what makes biology interesting. In years past, he defended reductionism (the idea that organisms can be adequately understood in terms Of physics, chemistry, and the history of evolutionary change) when it was not fashionable to do so. More recently, he has explored the insights to be gained by applying evolutionary theory to medicine. His 1996 book, Evolution and Healing: The New Science of Darwinian Medicine (coauthored with Randolph Nesse, of the University of Michigan Medical School), stresses the importance Of understanding the adaptive significance of symptoms such as fever rather than merely seeking immediate relief

George Williams taught biology for thirty years at the State University of New York at Stony Brook, where he is now professor emeritus. He is also editor of the Quarterly Review of Biology, which has been publishing thoughtful articles and book reviews about the life sciences for nearly three-quarters of a century. Williams's latest book, The Pony Fish's Glow and Other Clues to Plan and Purpose in Nature, was published by BasicBooks as part of its Science Masters Series.

Interview

Thirty years ago, in Adaptation and Natural Selection, you criticized some ideas in biology.

I think that my main criticism in that book was directed at the general assumption that adaptation characterizes populations and species, rather than simply the individuals in the populations and species. What I did was take the position that natural selection works most effectively at the individual level, and adaptations that are produced are adaptive for those individuals, in competition with other individuals of the same population, rather than for any collective well-being.

Individual selection would mean that living organisms are not adapted to prevent the extinction of their own species.

That is right. Most evolving lineages, human or otherwise, when threatened with extinction, don't do anything special to avoid it. I presume that the last pair of passenger pigeons, once a very abundant bird in North America, now extinct, reproduced the same old way. Once the species had gotten extremely rare, it did nothing new and did not take any special measures, the way an individual would if threatened with death. On other hand, we humans in fact have not gone extinct as yet; all our closest relatives have, so I would presume that to some extent the current human biology may be biased in favor of attributes that make us less vulnerable to extinction.

Just what features raise or lower vulnerability to extinction is a generally neglected problem, but it is widely recognized that sexual reproduction helps to keep a population going. Sexual reproduction is a complicated process that is occasionally lost, thereby simplifying the reproductive process. As a general rule, though, in both plants and animals, once a line of descent loses the sexual process, nothing new ever comes of it. It won't branch into several new species the way a sexual species might. So asexual reproduction exclusively in any line of descent appears to be a dead end. If there has ever been a mammal that reproduced asexually, it is not around any more and has no descendants.

If selection works at the individual level, why don't individuals live forever? Why do we grow old?

Well, no matter how fit you keep yourself, sooner or later something will get you: an accident, a new epidemic, an attack by terrorists, or whatever. Even if you had eternal youth, this would obviously not assure that you live forever. So the interesting question is, once we attain our full youthful adulthood, why don't we just stay that way?

Suppose we could do that: let's wave a magic wand, and suddenly we have eternal youth. In evolution that would not be stable, because eternal youth does not abolish mortality. Let's say that half of us with this eternal youth managed to live to 100, a quarter to age 200, one-eighth to 300, and so on. A mutation that would confer some slight advantage in our twenties and thirties might well be favored, even if it causes us to drop dead at age 300. Most people are going to be alive in their twenties and thirties and thus get the benefits of whatever that mutation does, but since only one-eighth of the population is going to reach-age 300, dropping dead then would be worth an advantage earlier in life. So the evaluation by natural selection of new genetic variability would be biased in favor of the earlier part of life histories and against the later part, until we had reevolved to something like the senescence we have now.