The Panda’s Thumb: More Reflections in Natural History
The Evolutionary Synthesis: Perspectives on the Unification of Biology
When I reviewed Stephen Jay Gould’s admirable Ever Since Darwin a few years ago, I expressed the hope that he would not lay his pen aside for too long. I need not have worried, for Gould is a natural writer: he has something to say and the inclination and skill with which to say it. His present collection is a series of essays that would give special pleasure to scientists, but they are sufficiently relaxed to be read with enjoyment by laymen too. A casual reader flipping through his pages may wonder what Mickey Mouse is doing in chapter nine (“A Biological Homage to Mickey Mouse”). Mickey is here to illustrate the characteristics thought by Konrad Lorenz to be responsible for the specially endearing characteristics of babyhood: “a relatively large head, predominance of the brain capsule, large and low-lying eyes, bulging cheek region, short and thick extremities, a springy elastic consistency, and clumsy movements.”
Without dissenting from Lorenz I wonder if this is the whole story. Few animals are more endearing than baby giraffes, which meet some but not all of Lorenz’s criteria; helplessness is surely another. I enjoyed this reminder of Mickey in his great days: it is a cultural tragedy that the brilliant early Disney was degraded and debauched by the witless and mindless imitators whose creatures have made television intolerable in the US on Saturday mornings.
Before I read Gould’s chapter fifteen I might have been tempted to dismiss as idiots people who enjoy such programs—but the correct technical term, I learn from Gould, is moron. Gould here adds his weight to those of us who insist that the pejorative and biologically most unsound term “Mongolism” be dropped in favor of “Down’s syndrome” as a designation of this unhappy congenital affliction. Down adopted the term because he regarded the syndrome as evidence of degeneration—of an atavistic return to a remotely ancestral human condition. Mongolian members of WHO objected to this and would have been still more annoyed if they had known that Down had entertained the possibility that the reversion was to a type even lower than that represented by modern Mongolians. Gould explains the whole matter admirably and in a way that everybody can understand. In defense of Down it should however be pointed out that Down worked and thought in the atmosphere of fearful wonderment about the implications for man of what was coming to be learned about heredity, development, and evolution that had been created by the writings of such as Francis Galton, Cesare Lombroso, Max Nordau, and of course Henrik Ibsen.
Gould’s favorite way of going about things is to pick upon some natural oddity and use it as a text for writing on some important biological problem. Thus the death within a few hours of birth of male mites of the genus Adactylidium is the text of the discussion of how the sex ratio comes to be fixed by natural selection. He adds, “Nature’s oddities are more than good stories. They are material for probing the limits of interesting theories about life’s history and meaning.” Thus Gould defends by implication (and quite rightly too) the dedicated bird watcher exultant in adding to his list of subjects the “rufous-crowned, peg-legged, speckle-backed, cross-billed and cross-eyed towhee.”
The chapter in Gould’s book that will arouse the most widespread interest (I first got wind of it in the European edition of the New York Herald Tribune) is that which has to do with an authentic nowhee: Piltdown Man. Between 1908 and 1912 an amateur archaeologist with some professional assistants came upon some rather puzzling bony remains in gravel in the village of Piltdown, Sussex, England. These were judged to be the remains of a very primitive man, Eoanthropus dawsoni (dawn man). In the gravel were also found some worked tools of flint and bone and some animal remains pointing to a find of great antiquity. Yet the fossil remains seemed inexplicably anomalous: for though the braincase looked very ancient and was unmistakably human, the lower jaw looked like that of an anthropoid ape.
No one knew what to make of it all and the anomaly was not clarified until the physical anthropologists J.S. Weiner and Kenneth Oakley with the moral support of Professor W.E. le Gros Clark divulged that the Piltdown skull was a fraud: some teeth had been artificially filed down, and aging of the human braincase had been simulated by the use of salts of chromium. Very many paleontologists had been skeptical all along and when the truth became known no living paleontologist of any distinction had reason to bemoan his gullibility. It was a disgraceful fraud and the question “Oodunnit?” still remains.
Suspicion has fallen on all the principals in the discovery, on the eponymous Charles Dawson and Sir Arthur Smith Woodward, author of The Earliest Englishman (London, 1948). Gould now makes a case against none other than Teilhard de Chardin, referring to A.S. Romer’s and Louis Leakey’s suspicion. That evidence is of course not direct: what it amounts to is that Teilhard could have been guilty. He was at a theological college in the neighborhood and was on Dawson’s team, and he had been on earlier expeditions during which he might have collected the fossil remains planted in the Piltdown gravel to give the finds an air of antiquity. There are also some anomalies of time and place in Teilhard’s letter to Kenneth Oakley congratulating him on his revelations.
Gould clearly had a good time following up his suspicions, and being a good writer he communicates his pleasure to his readers. But though Teilhard could have done it, I do not believe he did: I could as readily believe that he painted the supposedly paleolithic murals in the Lascaux caves (which like other cave paintings could probably do with a second look). The older Teilhard, the philosopher-scientist who wrote The Human Phenomenon, was in my very carefully considered opinion a silly old man, and the younger Teilhard can hardly be acquitted of gullibility, but I do not believe he was a criminal. The Piltdown forgery was a crime: “hoax” is too excusatory a word.
Gould writes sharply and amusingly about the considerations lying outside science that led to acquiescence in and even willingness to be deceived by the fraud. Clearly both racism and chauvinism played a part. The distinction—not yet quite the odium—of being the cradle of mankind is hotly competed for and Piltdown was in a way an Englishman’s answer to the disagreeable possibility that the earliest men may have been foreigners. In 1912 there would have been little dissent in England from the view that the English represented the highest evolutionary product of mankind, so what could be more natural than that the green and pleasant land should also have been the cradle of mankind?
What about the Panda’s Thumb? The essay that gives the book its title is a reflection prompted by Gould’s wonder at the skill with which the panda uses what is ostensibly its thumb to strip the leaves from bamboo shoots so that it can eat the stems. The puzzle is this: the hands and feet of vertebrates, though very variously modified, have characteristically five digits; the opposable thumb to which primates (such as ourselves and the manlike apes) owe so much of their dexterity is a modified finger, and there are four others. The panda, however, has five others. Does then the “thumb” represent a modified sixth finger? It is conceivable that it should because mutations affecting number and structure of the digits are by no means uncommon, but the panda’s thumb is not a digit at all. It is formed by the enlargement of a sesamoid bone at the end of the radius (a “sesamoid” is a supernumerary bone formed within a tendon or where a tendon rides over bone: the kneecap is one such). The panda’s hind foot has a counterpart in a tibial sesamoid that has not developed so far as the sesamoid in the hand.
The immediate purpose of Gould’s essay is to show how the opposable thumb could have developed making use of musculature already present and indeed already foreshadowed in the panda’s relatives the bears and raccoons. I think, though, that his more general purpose—especially laudable at a time when molecular biologists tend to elbow everyone else away from the limelight—was to show that comparative anatomy, in the tradition in which so many of us were brought up, is a most precise and exacting and certainly a very highly disciplined branch of biology, an opinion in which I heartily concur, knowing that in the hands of its really great practitioners comparative anatomy could almost be regarded as an art form. This does not mean that I depreciate molecular biology: it is not a matter of competition—there is room and need for both.
I very much hope that sociologists are among Gould’s readers and that they turn first to chapter eight, from which they may learn something to their advantage. Modern biologists are peevishly aware that amateur sociobiology is rapidly reaching the dimensions of a public nuisance. Evolutionary changes are thought to come about because it is desirable that they should do so, and behavioral traits are received into the genome, the organism’s set of chromosomes, “for the good of the species.” This is not a Darwinian notion. Edward O. Wilson was fully aware of the pitfalls in reasoning of this kind and that is why he settled upon “altruism” as the central theoretical problem in sociobiology. If the evolution of altruism can be explained, even in as extreme a form as “laying down one’s life for one’s friend” or committing a public-spirited suicide, as lemmings are alleged to do (I do wish Gould would look into this illusion—for such I believe it to be), then the occurrence of evolutionary changes “for the good of the species” would be very much easier to understand.
“Kin selection”—a notion of W.D. Hamilton’s—is widely agreed to be the key to the answer. The notion is made self-evident by a characteristic remark of J.B.S. Haldane’s, quoted by John Maynard-Smith, to the effect that he was prepared to lay down his life for two brothers or eight cousins. If there existed a genetic combination that conferred this degree of altruism upon Haldane it should increase his representation in the population because of the sharing of genes between blood relatives.
In the course of his discussion Gould quotes the aphorism that embodies one of the genuinely fundamental truths of biology: “that a chicken is just the egg’s way of making another egg.” I very much wish I knew who first said this. Gould attributes it to Samuel Butler, but Butler himself mentions it in his Notebooks (London, 1911) as a saying already familiar and in common use.
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.
Gould Was Right March 19, 1981