The Volubility of DNA

Scientists usually make their opinions and their findings known to each other through “papers”—contributions to learned societies or learned journals—by papers, that is to say, rather than by books. Every now and again there is a notable exception. One was Dobzhansky’s Genetics and the Origin of Species; a second was E. Mayr’s Systematics and the Origin of Species; a third, Simpson’s Tempo and Mode in Evolution. All three were published by the Columbia University Press: surely among the really notable publishing achievements of the twentieth century. The appearance of a new book by Dobzhansky prompted me to browse again in an older edition (1941) to see if I could recapture the excitement of reading a work which did more than any other to mark the distinction between the older evolution theory and the new.

The new evolution theory wedded Darwinism to Mendelian genetics. Many things changed. It was no longer believed that the evolution of organisms in the past was the work of a heroic macro-evolution quite different in kind from the petty and humdrum micro-evolution which can be shown to be at work today. No longer was it believed that the end product of an episode of evolution was the devising of some one genetic formula or “genotype” which represented the one highest possible degree of adaptedness of an organism to its environment. Instead of being regarded as a noisy epiphenomenon of an otherwise orderly and systematic process of evolution, inborn genetic diversity was shown to be universal in occurrence and significance, and indeed to be enforced by the action of natural selection.

Another idea which was superseded by the newer evolution theory was one I like to call the “dynastic” concept of evolution, which represents the evolutionary process by family trees much like those that illustrate the pedigrees of European royal families.

Unfortunately, alongside the newer evolution theory there grew up a conventional travesty that was described with contempt as “neo-Darwinism” by nature-philosophers who were not wise enough to keep their mouths shut. According to this travesty, what was, or was not, selected in the process of evolution was a mutant organism. When the environment of a population of organisms changes then the population has to change too. Fortunately, from time to time mutant organisms would appear which, so to speak, proffered their candidature for evolution. If they were the product of favorable mutations they were incorporated into the establishment, that is to say, they became part of what was still thought of as the genotype of the species. If not, they perished in the struggle for survival and were heard of no more.

What particularly enrages people who think that this travesty of evolution theory is what geneticists actually believe in is that mutation is avowedly a random process, so it would appear that the entire magnificent pageant of evolution culminating in no less an organism than H. sapiens was brought about by—chance!—a view which can be sustained only if we systematically neglect the elements in the evolutionary process that confer order and system.

Much of the confusion which surrounds the word “fitness” has at last been dissipated. It is natural that the layman should think of the word “fitness” in a sense which either means suitability in some rather exacting way, or calls to mind a middle-aged man flexing his muscles at an open window. Fitness in a genetical sense is something quite other than this. The term fitness refers to the contribution which some fraction of the population, by reason of its genetic endowments, makes to the population of the future. If some genetically distinctive fraction of the population takes more than its numerically fair share of being counted among the ancestors of the population of the future, then the genetic endowments that cause it to do so are said to confer fitness. One element in fitness is, of course, adaptability and not merely adaptedness, i.e., an ability to cope with exigencies that may arise in the future as well as with those that may confront a population of organisms today.

Modern evolution theory is fairly satisfactory as scientific theories go, but many people still have a sense of unease about it. It doesn’t really explain evolutionary progression, i.e., why it is that organisms seem, as it were, to propound increasingly difficult and complicated solutions to the problem of remaining alive in a hostile environment. Moreover, it is a little too facile, i.e., it is too difficult to think of phenomena that it can’t explain. This sounds a strange criticism, but long ago Popper convinced us that it is a just one.

What remains to be done in the study of evolution? Evolutionary genealogy is not likely to command great attention in the future. Tracing lines of evolutionary ascent among minor taxonomic groups was in any case never much more than a scholarly pastime. There will, however, remain fairly large groups, e.g., whales, the affinities of which are still uncertain or disputed. Here we may expect some help from the molecular biologist using the powerful new method of establishing homologies between the amino acid sequences of structural or other important proteins. In evolutionary theory itself, the real need, as it seems to me, is for a comprehensive theory of variation, i.e., of candidature for evolution, to account satisfyingly for the phenomenon I mentioned above, namely the tendency of organisms to find ever more complex solutions to the problem of remaining alive and perpetuating their kind.

This is one of those scientific problems that is so obvious that it is difficult to discern it in the round, as a problem. The writings of Teilhard de Chardin have been very much criticized, and rightly, I fear. But in “complexification” he surely put his finger on an important phenomenon. If we use the familiar figure of speech according to which the germinal DNA transmits a message from one generation to the next, then I think that one day a physico-chemical basis will be found for a certain volubility or repetitiousness of the DNA in transferring this message and this will provide the physico-chemical explanation of the tendency of plants and animals to become increasingly elaborate during evolution.

Can a layman grapple with Dobzhansky? I think so, if, like Dr. Johnson, he sets himself to it doggedly. But if anybody still possesses a copy of the first edition of Genetics and the Origin of Species he can either keep it or, in a mood of inexplicable generosity, send it to me. I will pay twenty dollars for a good clean copy. And this will enable the vendor to buy a brand-new copy of Genetics of the Evolutionary Process, and have some change as well.

Dobzhansky was himself the originator of many of the ideas of the new evolution theory. He is a considerable figure, therefore, but he is not too grand to reason with us and try to persuade us of the truth of what he says. Darlington is a very eminent authority on chromosomes but no one who has read his earlier work on The Facts of Life would expect any such courtesy from him. The style of his work is asseverative throughout. Consider this representative passage from the section in his new book entitled “The Hero and the Misfit.”

Consider the creative recombination. He is the inventor, the artist or the hero. He lies in the field of history and raises its greatest problem. But does he in fact change the course of history? The answer is that in terms of the ultimate destiny of man, which is probably extinction, he does not. But on the shorter view where the events of a few hundred years or the fate of a few nations seem to matter, he may alter it. For what we call great men are due to unique recombinations that occur at particular times and places. What they do affects the prospects of every other man who follows them. Sadly of course we must also admit that small men in great positions may have as great effect as great men in those positions. Their characters are equally determined. The difference almost by definition, is that their effects are never what they intended.

I leave it to the reader to guess at whatever Darlington can mean by the phrase “by definition” in this context.

Then consider the footnote on page 352 to which Professor Toulmin called my special attention. Here Darlington tells us that the tribe which provides the indispensable professional caste of grocery storekeepers in Algeria today is utterly homogeneous and homozygous. I wonder how he knows. I don’t believe it myself.

In the paragraph I have quoted above the dogma of genetic determinism shows through in the phrase “their characters are equally determined.” It has always seemed to me that strong adherence or repugnance to the dogma of genetic determinism raises a psychological rather than a scientific problem. This is a matter which deserves more attention than anyone has given it.

When an author knows or appears to know more than any one of his readers could be expected to know, the reader has to make up his mind about what degree of confidence he is to place in the author’s statements of fact or opinion. Each person will devise his own criterion. For some people, unreasonable people, I should say, the discovery of a single factual error or a single disagreeable opinion will destroy all confidence in the book. I myself go mainly by style. Phrases like “we may suppose that” something or other or this “may be thought of” as something else destroy my confidence in the author.

I am not altogether happy about the term “social evolution” especially in the context of the extreme form of genetic determinism that Darlington urges on us. Societies change, of course, and for quite long periods they may change in a directional and systematic way. Nevertheless, the hereditary nexus between one generation and the next is of a kind quite different from that which unites a lineage or organisms. It is nongenetic, for one thing—hence the use of the term “exosomatic” or “exogenetic” by people who have given some thought to the matter.

The propagation of knowledge and know-how, skills and beliefs is mediated through language and by example—in general, by indoctrination—or anyhow not by genes. I myself do not think that genetics throws very much light on the historic changes that have occurred in the great transformations of society. I had hoped that Darlington would change my views. The fact that he has not done so is to me one of the great disappointments of his book. After I had read it I did not feel enriched by any new insight into either history or sociology.