It is now more than a third of a century since research has been carried out, with increasingly profitable results, on the working hypotheses provided by the synthetic theory of evolution. According to the synthetic theory, organic evolution is satisfactorily explained, in principle and in many details, by the mechanisms of heritable variation and natural selection associated with the names of Darwin and Mendel, and integrated by Ronald Fisher. As I shall show below in connection with definite examples, these mechanisms leave no grounds for objections based on either unfamiliarity with genetics and populations studies (still unfortunately prevalent in some quarters, even among biologists), or on mysticism. Some people, unused to the laws of nature, rebel against the application of scientific determinism to problems of biology. They think that prevalent scientific views on evolution smell of “materialism,” existentialism, or Marxism, and they fondly hope, or wishfully think, that they can escape from the horns of such dilemmas through the eloquent but naive writings of Teilhard de Chardin. That charming man found a few fossils and believed in evolution, but this, unaccompanied by proficiency in genetics and ecology, did not make him qualify as a biologist. That he was a mystic is clear to biologists from the fact that, having rejected the explanatory value of adaptation for survival, he fell back on the proposition that if the tiger has flesh-tearing teeth, it is because, during its evolution, it acquired a “carnivorous soul” (une “ame de carnassier”). For all his value as a moralist, he can be allowed no claim whatever to having been a man of science, as Jean Rostand, George Gaylord Simpson, and Sir Peter Medawar have unanswerably, but charitably, shown.
Other people try to take refuge in hypotheses such as “Lamarckism,” which, as I shall show, is definitely disproved. Some long for the introduction of providential guidance into the argument, neglecting the fact that of the estimated 250 million species of plants and animals that have lived on earth, only 1 per cent has survived today, and of these, all too many are threatened with extinction. Such persons must also adapt themselves to the melancholy fact that countless animals expose other animals to the most atrocious suffering as part of their normal behavior. If this is providence, it is diabolical. Now comes another nonconformist, Adolf Portmann, who finds it difficult to accept that evolution is explicable in principle by the mechanism of natural selection working on heritable variation. So there is a confrontation.
IN BRITAIN and in North America, there have been eminent biologists whose work has influenced schools of teaching and research, not only in their own countries, but also, thanks to a common tongue, a shared system of thought, and close personal contacts, in each other’s land. The result has been that, on both sides of the Atlantic, there have long been generally shared points of view in most branches of biology, with respect to accepted principles and programs for further research.
At the same time, a parallel state of affairs obtains in continental Europe, where other eminent biologists have been interested in different problems, studied in different ways (the “Anglo-Saxons” would say, without paying sufficient attention to genetics and genetical ecology), with the result that the emphasis in teaching and research is not focused in the same directions, or in the same moulds, in Europe as in English-speaking countries. In the former it would seem that, in part, they are still fighting the battles that raged around Darwin a century ago over the question of pre-established purpose and design in evolution.
Adolf Portmann, of Basle, Switzerland, is one of the most distinguished continental biologists. In the book under review, New Paths in Biology, there is therefore not only an opportunity but a challenge for British and American biologists to take stock of what one of their foreign colleagues is doing, how he is thinking, and what he conceives to be the paths that biology should tread in future. These proposed new paths are not easy to discern.
In a stimulating opening chapter, the author lays down the principle that we study biology from two angles: that of matter, which, today, means molecular biology; and that of our subjective experience of life. It is well to make this clear at the outset, for throughout the book the subjective approach to the problem, which English-speaking biologists in general do not share, is never far from the author’s thought. The emergence of organisms and their parts from the molecular level he calls the “apparative stage,” which he defines as the world of organs: heart, brain, etc. Here he considers that the evolution of the cell nucleus was a more crucial step than that of the cell, because it allowed for the genetic mechanism of segregation and recombination, the re-shuffling and recombination, of genes (in astronomically high numbers of permutations) from both parents that occurs at the inception of every new generation; on this, as he very rightly says, the evolutionary process must rest. But was not the evolution of the structural pattern and adaptation of the cell itself, which is the basis of individuality and the organismal level of complexity, even more fundamental?
IN A DISCUSSION of Natural Form and Technical Shape, the author criticises the deficiency of what he calls “the technical understanding of organisms,” which, it appears, is the study of the technical efficiency of various functions. What he has in mind are such adaptations as the sonic radar equipment which enables bats to avoid objects when flying in the dark. Too much attention to analysis of this sort, he fears, exposes the biologist to the danger of neglecting the whole organism for the sake of its parts. Electronics and cybernetics have helped biologists to interpret many features of the structure and function of nervous systems, including the human, but, he says, “technical understanding can never provide more than a small glimpse of living reality.” With this we should be prepared to agree; but he goes on to say that this tendency towards technical understanding has had devastating effects on our view of nature, because it leads to concentration on “privileged forms” to the complete neglect of others. To the question, what are “privileged forms,” the answer is: those organisms which by reason of their coloration are particularly glaring or completely inconspicuous. He urges biologists to cease ignoring those forms that neither “strike” nor “deceive,” because there are so many “neutrals,” and to start with these. He gives no specific examples of such neutrals, but leaves the reader to think of the majority of plants and animals that show no obvious or visible adaptations, and neglects the fact, more and more inescapable as research proceeds, that adaptations are no less vital to the survival of the organism for being inconspicuous. As E. B. Ford has shown, whether the underside of a moth’s wings has one or two small spots is correlated with its success or failure in its environment; nobody yet knows why but the fact is there. Why it should be advantageous, in Portmann’s view, to start work on the “neutrals” is not immediately obvious, but Portmann goes on to explain this point and, at the same time, to introduce his philosophy. If, he says, the biologist fails to start with the “neutrals,” we should fail to see that there are so many forms whose significance cannot be reduced to mere functions of preservation. So there it is again, the old stumbling block of the significance to be attached to natural selection. This is now such a threadbare subject that “Anglo-Saxon” biologists should be reminded that generations have grown up who are imperfectly acquainted with the arsenal of new weapons which those who study evolution experimentally (yes, experimentally) now use.
To understand the basis of Portmann’s analysis it is necessary to realize that, while recognizing that selection exists as a process and a factor in evolution, he wants to free biological thinking from its hegemony. But it is legitimate to ask at this point what new path in biology is opened up here. Simply because so-called “privileged forms” show characters that have provided particularly profitable material for experimental analysis which has yielded results that have led to far-reaching general principles, are we invited to believe that such results are in some way invalidated, or restricted in scope? If Portmann would show how “unprivileged forms” can be made the subjects of successful experimental research (for there can be no acceptable “new path in biology” without this), all biologists would be grateful for the opening up of such a path.
THIS ALLEGED IMPERFECTION of the viewpoint of other biologists is, again, intelligible when one realizes that, for Portmann, the preservation of life (to which most biologists would consider that all adaptation tends) is not the paramount aim of organisms. From this he logically deduces that it should not be the paramount aim of organisms, and therefore that it should not be the paramount aim of study by biologists. He concludes that “far from deriding all subjective judgments, the biologist must merely try to understand the restrictive role they may play in all attempts to understand nature.” This injunction is aimed at the biologists who concentrate their attention on forms that “strike” or “deceive”—by which he means animals (and plants) that mimic others, or have warning, threat, or recognition marks, or sensational courtship behavior. But biologists who have specialized in such studies are not likely to be restrained from pursuing their researches on material which has already given them such valuable results and shows every promise of giving them more, nor will they agree that by concentrating on such material they have allowed their “subjective judgments” to blinker them in their understanding of nature.
In a chapter on “The Realm of Images,” Portmann makes a distinction between “outer” and “inner” phenomena, to which he attaches much importance. The former, which he calls “direct,” from their position on the surface of the body, “are directed at the eye of a possible beholder,” e.g., the pattern on the surface of the skin; the latter, which he calls “indirect” are not, e.g., the structure of the liver. This is no doubt true, but what is not clear is the author’s claim that “Our distinction between direct and indirect phenomena may be compared to the psychological distinction between conscious and unconscious processes.” What does this mean? And where is the new path in biology here? It all seems to be related to the distinction which the author made earlier between “privileged forms” that catch the eye, and the remainder that do not; for he is seriously worried by the problem of the origin of external colors and patterns of animals. Other biologists would add the color and patterns of plants to those of animals, but they seem to be less worried.
I have the impression that Portmann makes the distinction between “outer” and “inner” phenomena on the grounds that the latter, unseen by any beholder, cannot be explained by the gradual improvement of adaptation through natural selection. Yet there are many examples of internal adaptations which must have been improved by natural selection. F. C. Fraser and P. E. Purves have shown that the structure of the middle ear and its vascularization in whales provide adaptations which serve not only to equalize the pressure on both sides of the tympanic membrane at great depths, but to impart the sense of directional hearing to the whales (without which no male could find and meet any female), and also to remove nitrogen from solution in the blood and thus avoid “caisson-disease.” These advantages must have been conferred from the start by natural selection, enabling the whales to dive to increasingly great depths; yet all the structures concerned are internal and unseen.
THE EXTENT OF Portmann’s preoccupation may be seen in his statement that “either we look for survival mechanisms alone and restrict our research to the metabolic sphere, or else we look upon patterns and colors as ontogenetically determined structures and treat them as such.” It is difficult to see the need for this “either-or” alternative, these horns of a dilemma; for whether structures are “survival mechanisms” or not, they are all, in his sense, “ontogenetically determined.” By this he means that they arise during embryonic development because the fertilized egg has inherited genes that control them. Actually, this view is unacceptable to experimental embryologists and geneticists who know that the genetic inheritance is quite incapable, by itself, of producing normal development. What is inherited is a packet of genes which interact with the environmental factors to produce a series of responses by the organism; it is these responses that constitute development. If the factors of the environment are normal, the developed organism will probably be normal also; but any departure from normality in the environment will bring about an abnormality in the development. No structure can therefore be said to be “ontogenetically determined”; every structure owes its existence in part to the genetic inheritance, and in part to its interaction with the environment. It simply is not true to say that “all organisms develop along paths that are laid down in the germ”; it the environmental factors do not play a normal part in the process, organisms may (and do) develop into monsters, or fail to develop at all.
What the author seems to be striving after here is to avoid adopting the view that all patterns and colors are adaptive, confer survival value, and have arisen through selection. But no competent biologist would assert this. He would, however, assert that there is no deleterious character, color or pattern, or organ anywhere inside the body, that has not been acted upon adversely by selection, and either reduced (by the genes which control it becoming recessive in the manner that Ronald Fisher has shown) or extinguished by the death of its possessor. This is the explanation of the fact that the vast majority of mutant genes are now recessive. They have become recessive because they are unfavorable under the conditions in which they mutated; if they are too unfavorable, or “lethal,” their possessor dies. It must readily be admitted that the causes of the origins of patterns, colors, and of many other things, are not known. But Portmann maintains that “when it comes to the origins of animal patterns, the selection hypothesis is not only inadequate but offers no explanation at all, for a pattern can only conceal or warn once it is there.” Here it is necessary to disagree and to point out that there are countless examples of imperfect adaptations which have become perfected. This is particularly well shown in cases of Batesian mimicry, an adaptation whereby palatable organisms (butterflies have supplied the chief examples) mimic other species that are poisonous or unpalatable to predators and shunned by them after the experience of trying to eat them. In many cases of incipient states of mimicry, and in others where the mimics outnumber their models to such an extent that there is little survival value in copying a model which the predators have not thoroughly learned to shun (because they have successfully eaten so many palatable mimics), the mimetic patterns protect inefficiently (and the inefficiency can be measured by statistics of survival), but their efficiency can be and is improved by selection, as E.B. Ford and his colleagues have proved.
FURTHER ON in this chapter there are some statements which need to be quoted in order to bring out their import. In one of them the author says “as long as our view of living organisms is dominated by the idea that survival mechanisms alone are essential, we are necessarily forced to attribute the origin of all other structures to chance mutations.” The other runs, “we have those according to whom evolution is fully explained in terms of chance mutations,” and “those who consider that what mutations we can study or induce in the laboratory fail to provide an adequate explanation of the successive stages of evolution. There is no way of choosing between these two views.” As thus stated by him, there is indeed little to choose. But Portmann has not stated the case for the synthetic theory of evolution with these words, and the recurrence of “chance mutations” in his text raises, not for the first time, the suspicion that, in Europe, there has still been no full appreciation of the significance of Ronald Fisher’s integration of Darwinian selection with Mendelian genetics. Fisher’s experiments, demonstrations, and conclusions place him on the same level as Darwin and Mendel. It is on the basis of his work that the synthetic theory of evolution has been so admirably propounded by George Gaylord Simpson, Theodosius Dobzhansky, and Ernst Mayr, and is accepted teaching in Britain and North America. There is further evidence which also needs to be stressed: Colin Pittendrigh’s demonstration of the importance of the concept of teleonomic structures, structures which serve a purpose once they have arisen but which did not arise in order to serve that purpose.
What Fisher showed is that it is not mutation that controls evolution, but selection which governs the speed, direction, or cessation of evolution in accordance with ecological conditions. Mutation has no immediate evolutionary effects at all; what it does is to fill the genetic material of the organism with genes that mostly become recessive (and therefore do not show their effects under existing environmental conditions, unless inbred) until such time as changes in the other genes (which are organized into what is known as a gene-complex), or the environment, or both, make it possible for some one or other gene, by the sheer opportunistic play of ecological events, to exert effects even slightly beneficial. After this they become dominant (in the way that Fisher showed and E.B. Ford proved) and are incorporated in the standard genetic legacy from one generation to the next. This is not mere theorizing, but experimentally demonstrated fact. The vastly superior power of selection over mutation in changing an organism (selection pressures can now be measured, and no mutation has the slightest chance against any adverse selection), and the astronomically large possibilities of heritable variation resulting from segregation and recombination (“reshuffling”) of previously accumulated mutations, make it possible to say that if, fancifully, all mutation were to stop today, there is already in the various species sufficient potential heritable variation for natural selection to work on and to force evolution along in the future for as long as it has forced it up to now.
FISHER’S CONTRIBUTION to science is not exhausted by his dethronement of “chance mutation” as the explanation of evolution. Its implications, the predictions that have been made on them and verified, and the principles which they have established are numerous. Here, attention must be restricted to three or four aspects of the synthetic theory. Mutation may be random, but selection is not; it is rigorously determined by the prevailing ecological conditions, and as it is selection that determines the course of evolution, evolution is not the product of random chance. It is determined, but not predetermined, for the opportunistic and unpredictable play of circumstances that constitute an ecological environment rules out all possibilities that evolution has been pre-directed. There is also the fact that if evolution were pre-directed towards adaptation, there would be an observable “breeze” of favorable mutations; but the contrary is true. Of 221 mutations studied in the fruit-fly Drosophila, 208 are recessive (and therefore disadvantageous under the conditions in which they mutated), 11 are intermediate, and none dominant. If evolution were pre-directed by mutations the majority of them would be favorable, confer advantage at once, and would have become dominant. This means that all theories involving program-fulfilment, whether called orthogenesis, nomogenesis, Lamarckism, inheritance of acquired characters, or inner urges, are put completely out of court, and only selection is left as a mechanism that answers all the requirements of evolution, which paleontology as well as ecology has shown to be an opportunistic process.
Further, selection is a mechanism that can be described as producing high states of improbability, using this word according to the second law of thermodynamics, which shows that the ultimate equilibrium condition in the inorganic universe is random distribution of matter and energy. Improbability is different when viewed from time before and time after. The probability that any man alive today will have sons and grandsons and so on in the male line for one hundred generations is infinitesimally small; and yet every man alive today is a living witness to the fact that this event, however improbable it was one hundred generations ago, has nevertheless happened. Organisms, however “improbable” their production might appear to be, are no evidence of teleology or the purposeful production of beneficial effects by final causes. On the contrary, they are evidence for teleonomy, the purpose-serving effects of the unpredicted, opportunistic products of selection. Insofar as Portmann questions the competence of natural selection of heritable variation to account for evolution, and speaks against what he calls “chance mutations,” he lays himself open to the criticism that he is arguing in favor of some form of teleology and final causes, whether he realizes it or not. Some may even think that he has taken a step along the path of retreat to vitalism or metaphysics when he pleads that the biologist should “extend the concept of vital function to include what we have called the self-expression of living forms.”
PORTMANN’S PHILOSOPHY is succinctly given in two further paragraphs. In one statement, he claims that organic life is characterized not only by survival phenomena but also by what he has called “unaddressed” phenomena, which no other organism sees, and which he says “cannot have any kind of survival value” (he means that he cannot think of any). He therefore argues that “the germ is provided not only with survival structures, but also with phenomenal structures whose importance and number are at least as great.” This gives up all hope of a unifying principle in biology, and if this is his new path in biology, biologists can only wish him the best of fortune in proceeding along it. He must, however, forgive them, especially those who for forty years have profitably trodden other paths, not only if they stick to them, but also part company with him when he says “true knowledge can only spring from an open mind, a mind that is aware of what is still hidden and also of what must remain hidden forever.” How can a mind, even that of a biologist, know what it is that must remain hidden forever?
To most biologists, the new paths lie in the fields of genetics and molecular biology, which not only show promise of revealing the genetic code, but of providing at least a working model of the processes whereby living matter is built up from non-living, of replication which is at the base of all development, growth, reproduction, and regeneration, and of the way in which hormones act by de-repressing repressed genes. Portmann acknowledges this sensational break-through, and he is probably justified in issuing the warning that “the importance of molecular processes must not make us forget that life as such is never fully explained in molecular terms,” with which we would agree. But warnings and negative criticisms are not themselves new paths, and the biologist, when he lays down this book, will be grateful to the author for making him review and test all his own premises. But he will be likely to ask himself what new principles he is being invited to test, what new program he is being encouraged to undertake, and what new experiments he is being asked to make. For it is not clear.
April 14, 1966