The Ghost in the Machine
Neoteny in itself is of course not enough to produce these evolutionary bursts of adaptive radiations. The 'rejuvenation' of the race merely provides the opportunity for evolutionary changes to operate on the early, malleable phases of ontogeny: hence paedomorphosis, 'the shaping of the young'. In contrast to it, gerontomorphosis (geras = old age) is the modification of fully adult structures which are already highly specialised.* This sounds like a rather technical distinction, but it is in fact of vital importance. Gerontomorphosis cannot lead to radical changes and new departures; it can only carry an already specialised evolutionary line one more step further in the same direction -- as a rule into a dead end of the maze. To quote de Beer again:
The terms gerontomorphosis and paedomorphosis, therefore, express not only the stage in the life history of an animal with which they are concerned, but they also convey the meaning of racial senescence and rejuvenescence. It is interesting to note that as a result of considerations based on a different line of thought, Child had been led to express similar views. [5] 'If evolution is in some degree a secular differentiation and senescence of protoplasm, the possibility of evolutionary rejuvenescence must not be overlooked. Perhaps the relatively rapid rise and increase of certain forms here and there in the course of evolution may be the expression of changes of this sort.' [5a] * The word 'gerontomorphosis' was coined by de Beer as a contrast to Garstang's 'paedomorphosis'.
Draw Back to Leap
It seems that this retracing of steps to escape the dead ends of the maze was repeated at each decisive evolutionary turning point. I have mentioned the evolution of the vertebrates from a larval form of some primitive echinoderm. Insects have in all likelihood emerged from a millipede-like ancestor -- not, however, from adult millipedes, whose structure is too specialised, but from its larval forms. The conquest of the dry land was initiated by amphibians whose ancestry goes back to the most primitive type of lung-breathing fish; whereas the apparently more successful later lines of highly specialised gill-breathing fishes all came to a dead end. The same story was repeated at the next major step, the reptiles, who derive from early, primitive amphibians -- not from any of the later forms that we know.
And lastly, we come to the most striking case of paedomorphosis, the evolution of our own species. It is now generally recognised that the human adult resembles more the embryo of an ape than an adult ape. In both simian embryo and human adult, the ratio of the weight of the brain to total body weight is disproportionately high. In both, the closing of the sutures between the bones of the skull is retarded to permit the brain to expand. The back-to-front axis through man's head -- i.e., the direction of his line of sight -- is at right angles to his spinal column: a condition which, in apes and other mammals, is found only in the embryonic, not in the adult stage. The same applies to the angle between backbone and uro-genital canal -- which accounts for the singularity of the human way of copulating face to face. Other embryonic -- or, to use Bolk's term, foetalised -- features in adult man are: the absence of brow-ridges; the scantness and late appearance of body hair; pallor of the skin; retarded growth of the teeth, and a number of other features -- including 'the rosy lips of man which were probably evolved in the young as an adaptation to prolonged suckling and have persisted in the adult, possibly under the influence of sexual selection' (de Beer). [6]
'If human evolution is to continue along the same lines as in the past', wrote J.B.S. Haldane, 'it will probably involve still greater prolongation of childhood and retardation of maturity. Some of the characters distinguishing adult man will be lost.' [7] There is, incidentally, a reverse of the medal which Aldous Huxley pointed out in one of his later, despairing novels: artificial prolongation of the absolute lifespan of man might provide an opportunity for features of the adult primate to reappear in human oldsters: Methuselah would turn into a hairy ape.* But this ghastly perspective does not concern us here.
* Huxley, After Many a Summer. Some physical characteristics in the very old seem to indicate that the genes which could produce such a transformation are still present in our gonads, but are prevented from becoming active by the neotenic retardation of the biological timeclock. The obvious conclusion is that prolongation of the human lifespan is only desirable if it can be accompanied by techniques which exert a parallel influence on the genetic clock.
The essence of the process which I have described is an evolutionary retreat from specialised adult forms of bodily structure and behaviour, to an earlier or more primitive, but also more plastic and less committed stage -- followed by a sudden advance in a new direction. It is as if the stream of life had momentarily reversed its course, flowing uphill for a while, then opened up a new stream-bed. I shall try to show that this reculer pour mieux sauter -- of drawing back to leap, of undoing and re-doing -- is a favourite gambit in the grand strategy of the evolutionary process; and that it also plays an important part in the progress of science and art.
Figure 10 (on the next page) is from Garstang's original paper [7a], and is meant to represent the progress of evolution by paedomorphosis. Z to Z9 is the progression of zygotes (fertilised eggs) along the evolutionary ladder; A to A9 represents the adult forms resulting from each zygote. Thus the black line from Z4 to A4, for instance, represents ontogeny, the transformation of egg into adult; the dotted line from A to A9 represents phylogeny -- the evolution of higher forms. But note that the thin lines of evolutionary progress do not lead directly from, say, A4 to A5 -- that would be gerontomorphosis, the evolutionary transformation of an adult form. The line of progress branches off from the unfinished, embryonic stage of A4. This represents a kind of evolutionary retreat from the finished product, and a new departure towards the evolutionary novelty Z5-A5. A4 could be the adult sea cucumber: then the branching-off point on the line A4-Z4 would be its larva; or A8 could be the adult primate ancestor of man, and the branching-off point its embryo -- which is so much more like the A9 -- ourselves.
But Garstang's diagram could also represent a fundamental aspect of the evolution of ideas. The emergence of biological novelties and the creation of mental novelties are processes which show certain analogies. It is of course a truism that in mental evolution, social inheritance through tradition and written records replaces genetic inheritance. But the analogy goes deeper: neither biological evolution nor mental progress follows a continuous line from A6 to A7. Neither of them is strictly cumulative in the sense of continuing to build where the last generation has left off. Both proceed in the zigzag fashion indicated in the diagram. The revolutions in the history of science are successful escapes from blind alleys. The evolution of knowledge is continuous only during those periods of consolidation and elaboration which follow a major break-through. Sooner or later, however, consolidation leads to increasing rigidity, orthodoxy, and so into the dead end of overspecialisation -- to the koala bear. Eventually there is a crisis and a new 'break-through' out of the blind alley -- followed by another period of consolidation, a new orthodoxy, and so the cycle starts again.
But the new theoretical structure which emerges from the break-through is not built on top of the previous edifice; it branches out from the point where progress has gone wrong. The great revolutionary turns in the evolution of ideas have a decidedly paedomorphic character. Each zygote in the diagram would represent the seminal idea, the seed out of which a new theory develops until it reaches its adult, fully matured stage. One might call this the ontogeny of a theory. The history of science is a series of such ontogenies. True novelties are not derived directly from a previous adult theory, but from a new seminal idea -- not from the sedentary sea urchin but from its mobile larva. Only in the quiet periods of consolidation do we find gerontomorphosis -- small improvements added to a fully grown, established theory.
In the history of literature and art, the zigzag course is even more in evidence: Garstang's diagram could have been designed to show how periods of cumulative progress within a given 'school' and technique end inevitably in stagnation
, mannerism or decadence, until the crisis is resolved by a revolutionary shift in sensibility, emphasis, style.*
* See The Act of Creation, Book One, Chapters X and XXIII.
At first sight the analogy may appear far-fetched; I shall try to show that it has a solid factual basis. Biological evolution is to a large extent a history of escapes from the blind alleys of overspecialisation, the evolution of ideas a series of escapes from the bondage of mental habit; and the escape mechanism in both cases is based on the principle of undoing and re-doing, the draw-back-to-leap pattern.
Summary
After this anticipatory excursion, let me return for the last time to our starting point, the monkey at the typewriter. The monkey, according to the orthodox doctrine, is supposed to proceed by hit and miss, just as mental evolution, according to Behaviourist doctrine, is supposed to proceed by trial and error. In both cases, progress is secured by the stick-and-carrot method: the successful tries are rewarded by the carrot of survival or of 'reinforcement'; the harmful ones are weeded out by the stick of extinction, or by 'negative reinforcement'.
The alternative view which is here proposed does not deny that trial and error are inherent in all progressive development. But there is a world of difference between the random tries of the monkey at the typewriter, and the various directive processes summarised in preceding chapters -- starting with the hierarchic controls and regulations built into the genetic system, and culminating in the draw-back-to-leap pattern of paedomorphosis. The orthodox view implies reeling off the available responses in the animal's repertory, or on the Tibetan prayer-wheel of mutations, until the correct one is hit upon by chance. The present view also relies on trial and error -- each escape from a blind alley followed by a new departure is just -- that but of a more complex, sophisticated and purposive kind: a groping and exploring, retreating and advancing towards higher levels of existence. 'Purpose', to quote H.J. Muller again, 'is not imported into Nature. . . . It is simply implicit in it.' [8]
Each of the salient facts that I have mentioned has been separately known for some time, but their implications have mostly been ignored by orthodox evolutionists. Yet if these isolated facts and theories are worked into a synthesis, they make the problem of evolution appear in a new light. There may be a monkey hammering away at the typewriter, but that device is organised in such a way as to defeat the monkey. Evolution is a process with a fixed code of rules, but with adaptable strategies. The code is inherent in the conditions of our planet; it restricts progress to a limited number of avenues; while at the same time all living matter strives towards the optimal utilisation of the offered possibilities. The combined action of these two factors is manifested on each successive level: in the micro-hierarchy of the gene-complex, the canalisation of embryonic development, and its stabilisation by developmental homeostasis. Homologue organs -- evolutionary holons -- and similar animal forms arise from independent origins and provide archetypal unity-in-variety. The initiative of the animal, its curiosity and exploratory drive, act as pacemakers of progress; a quasi-Lamarckian mechanism of inheritance may in rare cases come to its aid; paedomorphosis offers an escape from blind alleys and a new departure in a different direction; and lastly, Darwinian selection operates within its limited scope.
The part played by a lucky chance mutation is reduced to that of the trigger which releases the coordinated action of the system; and to maintain that evolution is the product of blind chance means to confuse the simple action of the trigger with the complex, purposive processes which it sets off. Their purposiveness is manifested in different ways on different levels of the hierarchy; on each level there is trial and error, but on each level it takes a more sophisticated form. Some years ago, two eminent experimental psychologists, Tolman and Krechevsky, created a stir by proclaiming that the rat learns to run a maze by forming hypotheses. [9] Soon it may be permissible to extend the metaphor and to say that evolution progresses by making and discarding hypotheses, in the process of spelling out a roughed-in idea.
XIII
THE GLORY OF MAN
We are all in the gutter, but some of us are looking at the stars. Oscar Wilde
The activities of animal and man vary from machine-like automatisms to ingenious improvisations, according to the challenge they face.* Other things being equal, a monotonous environment leads to the mechanisation of habits, to stereotyped routines which, repeated under the same unvarying conditions, follow the same rigid, unvarying course. The pedant who has become a slave of his habits thinks and acts like an automaton running on fixed tracks; his biological equivalent is the over-specialised animal the koala bear clinging to his eucalyptus tree.
* See Chapter Eight.
On the other hand, a changing, variable environment presents challenges which can only be met by flexible behaviour, variable strategies, alertness for exploiting favourable opportunities. The biological parallel is provided by the evolutionary strategies discussed in previous chapters.
However, the challenge may exceed a critical limit, so that it can no longer be met by the organism's customary skills. In such a major crisis -- and both biological evolution and human history are punctuated by such crises -- one of two possibilities may occur. The first is degenerative -- leading to stagnation, biological senescence, or sudden extinction as the case may be. In the course of evolution this happened over and again; to each surviving species there are a hundred which failed to pass the test. Part Three of this book discusses the possibility that our own species is facing a crisis unique in its history, and that it is in imminent danger of failing the test.
The alternative possibility of reacting to a critical challenge is regenerative in a broad sense; it involves major reorganisations of structure and behaviour, which result in biological or mental progress. I shall try to show that both are based on the same draw-back-to-leap pattern, activating creative potentials which are dormant or inhibited in the normal routines of existence. In phylogeny, the major advances are due to the activation of embryonic potentials through paedomorphosis. In mental evolution something analogous seems to happen at each major turning point. The connection between the emergence of biological novelties and of mental novelties is provided by one of the basic attributes of living things: their capacity for self-repair. It is as fundamental to life as the capacity for reproduction, and in some lower organisms which multiply by fission or budding, the two are often indistinguishable.
Forms of Self-Repair
To understand this connection, we must proceed by a series of steps from primitive to higher animals, and finally to man. Needham has called regeneration 'one of the more spectacular pieces of magic in the repertoire of living organisms'. [1] Its most impressive manifestations are found in lowly creatures like flatworms and polyps. If a flatworm is cut transversely into two parts, the head-end will grow a new tail, and the tail-end will grow a new head; even if cut into six or more slices, each slice can regenerate a complete animal.
Among higher animals, amphibians are capable of regenerating a lost limb or organ. When a salamander's leg is amputated, the muscle and skeletal tissues near the wound-surface de-differentiate and assume the appearance of embryonic cells. [2] Around the fourth day, a blastema or 'regeneration bud' is formed, similar to the 'organ bud' in the normal embryo; and from then on the process follows closely the growth of limbs in embryonic development. The region of the amputation-stump has regressed to a quasi-embryonic state and displays genetic growth-potentials which are inhibited in normal adult tissues.* I have compared (p. 122) the gene-complex in a specialised cell to a piano with most keys inactivated by scotch tape; regenerating tissues have the whole keyboard at their disposal. The 'magic' of self-repair thus has a regressire (catabolic) and a progressive (anabolic) phase; it follows the undoing-re-doing pattern. 'The trauma plays a role similar to that of fertilisation in embryonic development' (Hamburger [4]). The shock triggers off the creative reaction.
* To be accurate, the origin of the materi
al which forms the blastema is still somewhat controversial; according to Hamburger [3], it is likely that it consists partly of de-differentiated cells, partly of undifferentiated mesenchyme-type connective tissue-cells, which fulfil a function similar to that of the 'reserve' or 'regeneration' cells in primitive organisms.
The replacement of a lost limb or lost eye is a phenomenon of a quite different order from that of adaptive processes in a normal environment. Regeneration could be called a 'meta-adaptation' to traumatising challenges. But the power to perform such feats manifests itself only when the challenge exceeds a critical limit. The regenerative capacity of a species thus provides it with an additional safety device in the service of survival, which enters into action when normal adaptive measures fail -- as the hydraulic shock-absorbers of a motor car enter into action when the limit of elasticity of the suspension springs is exceeded.