Nor, we may add, do Mendel's garden peas or the geneticist's fruit flies have any real bearing on 'evolution by natural selection'. Mendel's observations referred to such single traits as yellow seeds or green seeds, purple flowers or white flowers, etc., which were dependent on a single gene and were 'trivial' in the sense that they did not have any evolutionary significance. Similarly, all the mutations observed or induced in more than half a century of experimentation with Drosophila were either deleterious or trivial -- variations in the pattern of bristles on the fly's body, in the colour of the eyes, etc. Such isolated features which do not interact or interfere with the functioning of the organism as a whole, can indeed be safely left to the roulette wheel. In fact none of the mutations observed in millions of Drosophila have produced offspring showing any evolutionary advantage.
Once more the Darwinian theory, in spite of the invigorating injection of Mendelism, had come to a dead end. Bateson, who had been the first in England to greet the 'Mendelian dawn', was also among the first to express his disillusionment. Two years before his death in 1926, he told his son Gregory that it was a mistake to have committed his life to Mendelism, that this was a blind alley which would not throw any light on the differentiation of species, nor on evolution in general. [41]
Even earlier he wrote in Problems of Genetics:
The many converging lines of evidence point so clearly to the central fact of the origin of the forms of life by an evolutionary process that we are compelled to accept this deduction, but as to almost all the essential features . . . we have to confess an ignorance nearly total. The transformation of masses of population by imperceptible steps guided by selection is, as most of us now see, so inapplicable to the facts, whether of variation or of specificity, that we can only marvel both at the want of penetration displayed by the advocates of such a proposition, and at the forensic skill by which it was made to appear acceptable even for a time. [42]
Bateson coined the term 'genetics' and occupied the first university chair devoted to the new field in Cambridge. Wilhelm Johannsen, the Danish pioneer of neo-Darwinism, coined the term 'gene'. By 1923 he, too, realized that all the experimental evidence spoke against the theory: 'The Problem of Species, Evolution, does not seem to be approached seriously through Mendelism nor through the related modern experiences in mutations.' [43]
Yet the upholders of the theory, steeped in the mechanistic tradition, were apparently unable to see that random mutations of single factors -- 'atoms' of heredity -- were irrelevant to the central problem of evolutionary progress, which requires simultaneous, coordinated changes of all the relevant components in the structure and function of the organic holarchy. The geneticists' obsession with the bristles of the fruit-fly, and the behaviourists' obsession with the lever-pressing of the rat, show a more than superficial analogy: both derive from a reductionist philosophy which regards the living creature as a collection of elementary bits of heredity (Mendelian genes) or bits of behaviour (conditioned reflexes or operant responses).
6
I have quoted some voices of dissent coming from biologists in eminent academic positions. There have been many others, just as critical of the orthodox doctrine, though not always as outspoken -- and their number is steadily growing. Although these criticisms have made numerous breaches in the walls, the citadel still stands -- mainly, as said before, because nobody has a satisfactory alternative to offer. The history of science shows that a well-established theory can take a lot of battering and get itself into a tangle of contradictions -- the fourth phase of 'Crisis and Doubt' in the historic cycle* and yet still be upheld by the establishment until a breakthrough occurs, initiating a new departure, and the start of a new cycle.
* See above, Ch. VIII, 9.
But that event is not yet in sight. In the meantime, the educated public continues to believe that Darwin has provided all the relevant answers by the magic formula of random mutation plus natural selection -- quite unaware of the fact that random mutations turned out to be irrelevant and natural selection a tautology.
Towards the end of the last century Samuel Butler, another disenchanted Darwinian, wrote in his Notebooks:
I attacked the foundations of morality in Erewhon, and nobody cared two straws. I tore open the wounds of my Redeemer as he hung upon the Cross in The Fair Haven, and people rather liked it. But when I attacked Mr Darwin they were up in arms in a moment. [44]
Nearly a century later, the emotional reactions to such lèse majesté are still much the same.
7
In the 1950s a new popular symbol was added to Newton's apple and Mendel's peas: the double helix. The unravelling of the chemical structure of DNA, the nucleic acid in the chromosomes, carrier of the 'hereditary blueprint', was in itself a remarkable achievement and focused attention on the new field of molecular biology or molecular genetics. At first it looked -- as had been the case with Mendel's laws -- like a heavenly gift to neo-Darwinism, but it soon turned out to be more of a Trojan horse: the new insights gained into the infinitely complex bio-chemistry underlying the 'strategy of the genes' finally demolished the naively simplistic model of Mendelian genetics.
In the earlier versions of the model, the chromosomes were represented as the keyboard of a grand piano with millions of keys.* The fertilized egg had the whole keyboard at its disposal. As the embryo developed and each cell became differentiated, most of its keyboard was sealed off by 'scotch tape' and only those keys remained operative which served the cell's specialized functions. The 'scotch tape' is called in the language of genetics a 'repressor'. The agent which strikes the key which activates the gene at the required time is an inducer or 'operator'. A mutated gene is a key which has got out of tune. On some occasions, when quite a lot of keys have gone quite a lot out of tune, the result, we were asked to believe, was a wonderful new melody -- a reptile transformed into a bird, or a monkey into a man.** Somewhere along the line the theory had obviously gone wrong.
* See above, Ch. I, 9. ** This may sound like a malicious caricature of the theory. However, I used this musical simile for the first time in The Ghost in the Machine (1967) and three years later Monod himself endorsed it, as it were: 'Even today,' he wrote [45], 'a good many distinguished minds seem unable to accept or even to understand that from a source of noise natural selection alone and unaided could have drawn all the music of the biosphere.' Another metaphor, approved by geneticists, compares mutations (during replication of the chromosomes) to copying errors committed by careless typists. [46] Grassé commented: 'The monks of the Middle Ages made copying errors which altered and corrupted the texts which they had to reproduce. Who would dare to pretend that these mistakes constitute the works?' [47]
The point where it went wrong was, as we have seen, the atomistic concept of the gene. At the time when genetics got into its stride, the nineteenth- century type of atomism was being abandoned by physicists, but was still in full bloom in the life sciences: reflexes were atoms of behaviour, and genes were atomic units of heredity. A certain gene was responsible for straight or curly hair, another for haemophilia; and the organism was represented as a mosaic composed of these elementary units. But by the middle of our century these rigidly atomistic concepts of Mendelian genetics had been considerably softened up -- and had actually become fluid. It was realized that a single gene may affect a wide range of different characteristics (pleiotropy). And vice versa, a great number of genes may interact with each other to produce a single characteristic (polygeny). Some trivial feature, such as the colour of the iris, may depend on a single gene, but the hereditary configuration of all important features of the organism depends on the totality of genes -- the gene complex or 'genome' as a whole. Thus by 1957 one could read statements like the following in respectable biology textbooks:
All genes in the total inherited message tend to act together as an integrated whole in the control of development . . . It is easy to fall into the habit of thinking that an organism has a set number of charact
eristics with one gene controlling each character. This is quite incorrect. The experimental evidence indicates clearly that genes never work altogether separately. Organisms are not patchworks with one gene controlling each of the patches. They are integrated wholes, whose development is controlled by the entire set of genes acting co-operatively. [48]
This is a far cry from the earlier versions of the theory. In those early days of genetics, a gene could be 'dominant' or 'recessive', and that was about all there was to know about it. But with the advent of molecular biology, phenomena of previously undreamt-of complexity entered into the model (just as in sub-atomic physics), so that more and more terms had to be coined and added to the vocabulary: repressor genes, with co-repressors and apo-repressors; modifier genes, switch genes, operator genes which activate other genes, 'cistrons' and 'operons' (Monod) which constitute sub-systems of interacting genes (we might call them 'genetic holons'), and even genes which regulate the rate of mutations in genes. While the activities of the chromosomes had originally been conceived like the unfolding of a linear sequence as on a tape-recorder, it should have gradually become apparent that the genetic controls in the cells of the developing embryo operate as a self-regulating micro-hierarchy, equipped with feedback devices from a hierarchy of environments* which surrounds each and every cell.
* See above, Ch. I, 9.
Such a holarchy -- unlike a recording tape or a 'blueprint' -- must be conceived of as a stable, flexible affair. Yet it must to a large extent be self-regulating and capable of self-repair. It must not only protect the growing embryo against the hazards and buffetings to which it is exposed, but also protect the species against the evolutionary hazards of phylogeny -- the random mutations occurring in its own chromosomal genes.
The conception of a 'genetic micro-hierarchy'* is still regarded with scepticism or hostility among the hard core of the defenders of the synthetic theory -- mainly, perhaps, because its acceptance would lead to a basic revaluation of our notions of the evolutionary process -- as will be seen in subsequent chapters.
* A term first proposed, as far as I know, by L. L. Whyte.
8
Unlike the current metaphor of the 'genetic blueprint' which gives the impression of a fixed topological map to be mechanically copied, the concept of a 'genetic hierarchy' implies that the selective and regulative controls in the organism operate on several levels.
The lowest levels are concerned with eliminating harmful variations in the genetic material; the higher levels with coordinating the effects of acceptable changes. The mystery, as we shall see, lies in the operation of the higher levels -- the coordination (or orchestration) of those changes which transform the amphibian egg into a reptilian egg, and a reptile into a bird. But first, I must say a few words about the operation of the lower levels.
Several biologists (among them von Bertalanffy, Darlington, Spurway, Lima-de-Faria and, more recently, Monod) have suggested that the evolutionary screening process -- the action of the 'selective weedkiller' -- might start inside the organism, on the level of the molecular chemistry of the genome itself. Mutations are alterations in the sequence of the chemical units in the chromosomes (the four letters of the genetic alphabet); they have been compared to the copying errors of mediaeval monks which corrupted the antique texts. [49] The concept of 'internal selection' launched by the biologists just quoted, implies that there is a hierarchy of correctors and proof readers at work to eliminate the misprints. In the orthodox theory, natural selection is entirely governed by the pressures of the external environment, which kills off the unfit and blesses the fit with abundant progeny. In the light of the foregoing, however, any chromosomal change, whatever its cause, must pass the tests of internal selection for physical, chemical and biological fitness before being let loose as an evolutionary novelty. Thus the concept of a genetic micro-hierarchy imposes strict limitations on the range and evolutionary impact of random mutations and reduces the importance of the chance factor to a minimum. The proverbial monkey at the typewriter works in fact on a very sophisticated machine which the manufacturers have programmed to print only words which convey meaning and to erase nonsense syllables automatically.* Thus the hierarchic model at least enables us to get rid of the monkey-typist and of Monod's roulette wheel. It does not answer the ultimate question who or what programmed that prodigious typewriter, but it puts the question mark where it properly belongs and enables us to approach the problem step by step as we move on to higher levels of the genetic hierarchy.
* This metaphor is almost literally applicable to mistakes made in the protein manufacture in micro-organisms due to 'nonsense syllables' appearing in the RNA. [50]
The next step leads us to the remarkable powers of regeneration and self-healing which reside in the gene-complex as a whole, or a substantial sub-assembly of it. These powers are demonstrated by experimental embryology; we remember (p. 41) that if, in the early stages of development of the newt embryo, the tissue which would normally develop into its tail, is transplanted into the position of a future leg, that tissue will grow not into a tail, but into a leg. Such magic is not confined to ontogeny; it can also be observed in phylogeny. I have given one example among many in The Ghost in the Machine:
The fruit-fly has a mutant gene which is recessive, i.e., when paired with a normal gene, has no discernible effect . . . But if two of these mutant genes are paired in the fertilized egg, the offspring will be an eyeless fly. If now a pure stock of eyeless flies is made to inbreed, then the whole stock will have only the 'eyeless' mutant gene . . . Nevertheless, within a few generations, flies appear in the inbred 'eyeless' stock with eyes that are perfectly normal. The traditional explanation of this remarkable phenomenon is that the other members of the gene-complex have been 'reshuffled and re-combined in such a way that they deputise for the missing normal eye-forming gene'. [51]
But no biologist has been so perverse as to suggest that the new eyes evolved by pure chance, thus repeating in a few generations an evolutionary process which took millions of years. Nor does the concept of natural selection provide the slightest help. The re-combination of genes to deputize for the missing gene must have been coordinated according to some overall plan, or set of rules, governing the action of the gene-complex as a whole. It is this coordinating activity, originating at the apex of the genetic hierarchy which ensures both the genetic stability of species over millions of years, and their evolutionary modifications along biologically acceptable lines. The central problem of evolutionary theory is how this vital coordinating activity is carried out. This is where the big question mark comes in. The metaphor has shifted from the croupier at the roulette wheel to the conductor directing his orchestra.
This shift was already foreshadowed by some of the founding fathers of neo-Darwinism who became dissenters, such as Bateson and Johannsen. The latter (who, we remember, coined the term 'gene') wrote that after all the minute effects of Mendelian mutations had been taken into consideration, there would still remain 'a gteat central something' which contained the clue to the enigma. [52]
Waddington had an ambivalent attitude to the official theory; I have quoted him poking fun at evolution-by-chance-mutation; on the other hand, he wanted to avoid a complete break with the Darwinian doctrine. As a way out of the dilemma, he proposed in a much-quoted broadcast lecture that in the evolution of a complex organ, such as the human eye, a chance mutation may 'affect the whole organ in a harmonious way'. This implies that the mutation affecting a single component -- say, the lens -- acts merely as a trigger on a complex pre-set system which has been programmed to react 'in a harmonious way' (our 'programmed typewriter'); and that this programming is also inherited, i.e., represented on a higher level of the genetic hierarchy. Moreover, the harmonious evolution of seemingly unrelated organs (i.e., the wings, air-sacs and digestive system of birds) is coordinated at an even higher level -- the 'great central something' at the apex of the hierarchy.
Jacques Monod was confronted with th
e same dilemma. His brave attempt in Chance and Necessity to defend the beleaguered citadel could be compared to Custer's Last Stand. Though he keeps repeating that 'chance alone is at the source of all creation in the biosphere', etc., he is compelled by the evidence derived from his own field to acknowledge the existence of the 'great central something' by postulating a second basic principle of evolution besides chance, which he calls teleonomy (his italics):
One of the fundamental characteristics common to all living beings without exception [is] that of being objects endowed with a purpose or project, which at the same time they exhibit in their structure and carry out through their performances . . . [53]
The cornerstone of the scientific method is . . . the systematic denial that 'true' knowledge can be got at by interpreting phenomena in terms of final causes -- that is to say, of 'purpose' . . . Objectivity nevertheless obliges us to recognize the teleonomic character of living organisms, to admit that in their structure and performance they act projectively -- realise and pursue a purpose. .. [54]
But what, one might ask, is the difference between Monod's 'teleonomy' and the good old Aristotelian teleology, defined by the Concise Oxford Dictionary as the 'doctrine of final causes, view that developments are due to the purpose or design that is served by them'? And even more shockingly, does not the passage quoted remind one of the Lamarckian heresy, according to which evolution is nature's reponse to the organisms' needs? Grassé commented: