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Back to Evolution

The connection between the two books under review is that the author of the first is a contributor to the second, which has also to do with evolution. Gould’s contribution is on the bearing of paleontology upon modern evolutionary theory—an intractable subject; so I was not surprised to learn, though I did so for the first time, that “Darwin himself viewed paleontology more as an embarrassment than as an aid to his theory.” George Gaylord Simpson was the first man to make fossils give convincing evidence of the rate and pattern of evolution and Gould’s homage to him reminded me of the great sense of excitement I felt when, as a graduate student of zoology who had been brought up in an almost monastically severe discipline of comparative anatomy, I first read Simpson’s Tempo and Mode in Evolution (1944).

Laymen may be surprised to learn that so long after Darwin and the routing of Bishop Wilberforce, evolution is still a live topic. It is the mechanism of evolution, not the acceptability of the hypothesis, that is still in question. As to the hypothesis itself there are still many laymen who do not believe that the Earth is spherical. In evolution theory, though, there is no one “proof” of evolution as crushingly decisive as the satellite and lunar pictures of the Earth that showed it beyond doubt to be a sphere. The reasons that have led professionals without exception to accept the hypothesis of evolution are in the main too subtle to be grasped by laymen. The reason is that only the evolutionary hypothesis makes sense of the natural order as it is revealed by taxonomy and the animal relationships revealed by the study of comparative anatomy, much as the notion of the roundness of the earth underlies all geodesy and navigation.

In biosystematics and comparative zoology the alternative to thinking in evolutionary terms is not to think at all. T.H. Morgan himself regarded the embryological evidence alone as virtually decisive: he had in mind the curious pattern of development according to which animals as they grow up tend often to recapitulate the embryological history of what are presumed to be their ancestors. Their is indeed a certain stage in the development of fish, frogs, reptiles, and mammals—that in which the principal structures of the embryonic axis are laid down—in which the embryos of all these animals, so very different as adults, are so similar to each other that one has to be quite an expert to tell them apart. The phenomenon of “recapitulation” is totally unintelligible except in the light of evolutionary descent; but in spite of the general acceptance of the evolutionary hypothesis and of the notion—accepted by virtually all professional biologists—that natural selection is its principal agency, many matters of detail still remain to be resolved.

These are the subject of The Evolutionary Synthesis, a good workmanlike professional job addressed to an informed audience. The contributions are knit together by the skill and distinction of the two editors. Ernst Mayr, recounting the opposition to Darwinian theory, recalls that during the 1920s and 1930s (and a good deal earlier than that, I should say) evolutionary biologists were divided into two camps, the geneticists on the one hand and the naturalists-systematists on the other. The “modern synthesis” that is so often referred to is a synthesis of these two camps. It was the reformulation of the theory of evolution in the concepts and the language of modern genetics. Underlying it all was what may be called the “population-dynamical” style of thought, the adoption of which called for a huge reorientation of mind.

The systematists and comparative anatomists accustomed us to the “family tree” way of looking at evolutionary change and most people can remember from their schooldays those branching trees which, if they related to vertebrate animals, started with lowly animals such as Amphioxus and went up a branching tree through fish, amphibia, early reptiles, and the two great dynasties of more modern reptiles known as birds and mammals. At the tip of the mammalian tree were the primates, Simiidae and Homo, whose genealogical tree it really all was.

The concepts of population dynamics did away with the dynastic or typological representation of evolution and substituted for it the new notion that it is not the lineages of descent but whole animal populations that undergo evolution. Demographers such as Alfred J. Lotka of the Metropolitan Life Insurance Company and the Italian mathematical physicist Vito Volterra made contributions to evolutionary theory that are still well remembered. The most important single innovation in the modern synthesis was however the new conception that a population that was deemed to undergo evolution could best be thought of as a population of fundamental replicating units—of genes—rather than as a population of individual animals or of cells. Sewall Wright, who has only now in his ninetieth year been recognized by the Darwin Medal of the Royal Society of London, was a principal innovator in this new way of thinking—a priority for which R.A. Fisher, an important but lesser figure, never forgave him just as he never acknowledged his indebtedness to Lotka for one of his germinal ideas. The third name commonly mentioned in the same breath is that of J.B.S. Haldane.

Thanks to the work of these three pioneers natural selection can now be measured—essentially in terms of the net reproductive advantage of the replicating unit. This is essentially a measure of the degree to which the unit prevails over competitors or alternatives in the population: thus black or dark-colored moths prevail over their lighter competitors where they enjoy a net reproductive advantage amidst the sooty foliage of an industrial countryside. That is the explanation, not—as Heslop Harrison and a few others thought—because of the inheritance of an adaptation acquired during the moths’ individual lifetimes. This latter would be a so-called “Lamarckian” interpretation which, though it appeals to literary folk and other amateurs (among them George Bernard Shaw and Arthur Koestler), is now rejected by almost all professional biologists. So far Lamarckism has failed every critically designed test it has been put through.

Quite recently what has been described as a paradigm of all adaptive processes—rightly so because of our complete confidence that a rabbit not yet born will be able to make antibodies against a chemical not yet synthesized—i.e., the mounting of a specific immune response directed against a non-self substance that intrudes into the body, has been thought to enjoy a Lamarckian mode of inheritance. That is, the immune response is thought to bring about a genetic change which reproduces the adaptation in the next generation, without the intervention of selection. Some of my colleagues have been considering this possibility intently in the past few months without however convincing the more critical among them of the truth of the notion.

It is fitting that that great pioneer of genetics Thomas Hunt Morgan of Columbia should have been the first to recognize quite clearly the context in which Lamarckism does obtain—that of cultural inheritance, or as Julian Huxley put it, “psychosocial evolution.” There is a pedagogic tradition that a blacksmith is normally called upon to testify on these occasions; and the evidence he gives is that although a blacksmith’s son will not inherit brawny arms because his father has them, he is quite likely to acquire them because his father teaches his son his trade and introduces it to him early in life. Morgan and his school are the subject of a contribution by Theodosius Dobzhansky, a member of that school and one of the greatest figures in modern evolutionary genetics. When Dobzhansky joined him Morgan was getting on in years and, being thoroughly honest and hating cant, admitted that the modern flights of drosophila genetics, the subject he himself founded, were getting a bit beyond him.

No one who has listened to the in-talk of graduate students of genetics will think this at all surprising. A rather similar fate confronted Bertrand Russell when he met with young practitioners of mathematical logic at a New York university. I do not think this a tragic situation because both Morgan and Russell must have felt proud of the latterday accomplishments of what were, after all, their respective brain children; the only sadness is that in situations such as this the young sometimes take pleasure in seeing their eminent seniors panting to keep up with them but falling ever farther behind.

In Dobzhansky’s account of him Morgan comes out as a rather mixed figure: he used the word “naturalist” as a term of contempt and did not therefore do much to unite the two camps to which Mayr refers in his introduction. In the control of laboratory expenditure Morgan was ridiculously stingy. I wonder what he would have made of the modern vogue for the disposable equipment that is used once and then thrown away: very likely, like some senior biologists I know, he would have washed it and insisted on using it again. But in spite of this he was generous with his private funds and during the depression years he helped several students without letting them know where their subsidy came from.

Symposia such as this very seldom escape the charge of being rootless—of being so busily engaged with immediate problems and personal interests as to overlook altogether the history of the ideas under discussion—each problem being treated as if it had come up for the first time. No such charge can be made against the present symposium. One of its most attractive characteristics—that which is most likely to make the book endure—is the discussion of the evolution of evolutionary thought among the pioneers of the New Synthesis and in the various countries in which it slowly took shape.

France is very often the odd man out on these occasions and Ernst Mayr remarks of it that “France is the only major scientific nation that did not contribute significantly to the evolutionary synthesis.” Ernest Boesiger’s excellent article frankly admits the degree to which chauvinism colored French appraisals of Darwinism and explains how in rediscovering Lamarck they “made him into something very different from what his ideas actually convey.”

Major British geneticists are written on by C.D. Darlington in an article that reveals more about the author than about his subjects. Darlington sat next to J.B.S. Haldane for twelve years but “usually got no ideas from him” in connection with his research. This was quite a feat, for Haldane was full of ideas, many of which have been profoundly illuminating. When Haldane joined the Communist Party Darlington drifted away from him. Here I sympathize, for Haldane was a communist of the unteachable kind: when Beria fell from grace in Russia I can remember saying to Haldane, “Surely, Haldane, you don’t believe Beria was in the pay of the Americans all that time?” “One can’t be sure,” he said, “people in high positions often get careless.” I wish I had taken the opportunity to remind him of what the Duke of Wellington once said to the lady who came on to him with the words “Mr. Smith, I presume?” His words were, “Madam, if you believe that, you can believe anything.”

Darlington manages to be sneery and disagreeable about William Bateson, the man who coined the word “genetics” and whose famous and influential Mendel’s Principles of Heredity (1909) really put Mendelism on the map. Perhaps because of his preoccupation with himself Darlington fails to quote the remark of Bateson’s that characterizes him most completely. In the work to which I have just referred Bateson said of evolutionary theory in the decades following Darwin that it was “marked by the apathy characteristic of an age of faith.” He went on: “Everyone was convinced that natural selection operating in a continuously varying population was a sufficient account of the origin of species except the one class of scientific workers whose labours familiarise them with the phenomenon of specific difference.” He then went on to call attention to the dichotomy to which Ernst Mayr refers in his introduction to the symposium as a whole.

I expect that what sickened Bateson about the contemporary form of Darwinism was its explanatory glibness, the difficulty of devising any critical test of a formula as accommodating as that which came to be associated with Darwin’s name. The symposium I am reviewing is evidence enough that apathy has been dispelled and that biologists again consider evolution as a centerpiece of their thinking.

Letters

Gould Was Right March 19, 1981

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