The manufacturers know that it does not pay to design a new model from scratch, by starting on the level of elementary components; they make use of already existing, standard components -- chassis, brakes, etc. -- each of which has developed out of long previous experience, and then proceed by relatively small improvements or modifications of some of these -- for instance, by re-designing the body-line, or improving the cooling system, or introducing bucket seats.
Similar restraints can be shown to operate in biological evolution. Compare the front wheels of the latest model with those of a pre-war vintage car -- they are based on the same principles. Compare the structure of the forelimbs in man, dog, bird and whale, and you find that evolution has retained the same basic design:
The human arm and the bird's wing are called homologous organs because they show the same structural design -- of bones, muscles, blood vessels and nerves -- and are descended from the same ancestral organ. The functions of arm and wing are so different that it would be logical to expect each to have a quite different design. In fact, evolution proceeded, just as car manufacturers do, by merely modifying an already existing component (the forelimb of the reptilian ancestor, from which birds and mammalians branched out more than two hundred million years ago), instead of starting from scratch. Once Nature has taken out a patent for manufacturing a component organ, it sticks to it tenaciously: the organ or device has become a stable evolutionary holon.
This principle holds all along the line, from the sub-cellular level to the 'wiring diagram' of the primate brain. The same make of organelles functions in the cells of mice and men; the same make of contractile protein serves the motion of amoeba and of the pianist's fingers; the same four chemical units constitute the alphabet of heredity throughout the animal and plant kingdoms -- only the words are different for every creature. The proverbial lavishness of Nature is compensated by its less obvious conservatism and parsimony -- one might almost call it stinginess -- of basic homologous designs, from organelles to brain structures. 'This concept of homology', wrote Sir Alister Hardy, 'is absolutely fundamental to what we are talking about when we speak of evolution. Yet in truth', he added wistfully, 'we cannot explain it at all in terms of present-day biological theory'. [7]
The reason for this failure is, as we have seen, that the orthodox theory assumed homologous structures in different species to be due to the same 'atomic' genes inherited from the common ancestor (though modified by mutation in the course of their long descent); whereas there is now ample evidence that homologous structures can be produced by the action of quite different genes. The only way out of this cul-de-sac seems to be to substitute for genetic atomism, which has so drastically broken down, the concept of the genetic micro-hierarchy, with its own built-in rules, that permit a great amount of variation, but only in limited directions on a limited number of themes. This really amounts to the revival of an ancient idea which goes back to Goethe -- and even further to Plato. The point is worth a short historical digression -- which may make it clear why the concept of homology has such great importance not only for the biologist, but also for the philosopher.
Archetypes in Biology
Long before Darwin, naturalists were divided into evolutionists (Buffon, Lamarck, St. Hilaire, etc.), and anti-evolutionists who believed that the Creator had put down the first giraffe, mosquito and walrus simultaneously as ready-made products on the earth. But both pro- and anti-evolutionists were equally struck by the similarity of organs and designs in otherwise widely different species. The term 'homologue organ' was actually coined by Geoffroy St. Hilaire. His Philosophie Anatomique, published in 1818, starts with the question: ' . . . Is it not generally acknowledged that vertebrates are built up on one uniform plan -- e.g., the forelimb may be modified for running, climbing, swimming or flying, yet the arrangement of bones remains the same . . .?' [8]
Goethe had become an evolutionist long before that, through his studies of the morphology (a term which he coined) of plants and animals. In his Metamorphosis of Plants, published in 1790, he postulated that all existing plants could be derived from a common ancestor, the Urpflanze or arche-plant; and that all the organs of plants are homologous* modifications of a single structure, expressed in its simplest form in the leaf. Though Goethe was already at the height of his fame, the Metamorphosis had a hostile reception (incredible as it seems, his own publisher in Leipzig rejected it, and he had to go to Cotta in Gotha); but it had considerable influence on the German Naturphilosophen, who combined comparative anatomy with transcendental mysticism. These men were not evolutionists, but they were fascinated by the universal recurrence of the same basic patterns in the design of animals and plants; they called them 'archetypes' and thought that they constituted the key to the Lord's design of creation.
* Though he does not use the word.
The idea that all the existing flowers, trees, vegetables and so on are derived from a single ancestral plant seems to have occurred to Goethe during his sojourn in Sicily, where he had spent most of his time in botanising. After his return, in 1787, he confided to Herder:
I have seen the main point, the core of the problem, clearly and beyond doubt; everything else I can already see, too, as a whole, and only a few details need working out. The ancestral plant will turn out to be the most wondrous creation of the world, for which Nature herself shall envy me. With the aid of this model and the key to unlock it, one can then invent further plants ad infinitum which, however, must be consistent; that is to say, plants which, if they do not exist, yet could exist; which, far from being shadows or glosses of the poet's or painter's fancy, must possess an inherent rightness and necessity. The same law applies to all the remaining domains of the living. [9]
The conditions of 'inherent rightness and necessity', to which all existing and possible forms of life must conform, Goethe was of course unable to define; but his intuition told him that they could not include fanciful, arbitrary patterns created by the unbridled imagination of painters -- or science-fiction writers. They must conform to certain archetypal patterns, limited in their range by the basic structure and chemistry of organic matter. Evolution cannot be a random process, pulling in bits here, pulling out bits there. It must conform to some orderly design, like 'the stern, eternal laws which guide the wandering planets in their orbits'.*
* Faust, Prologue.
Goethe's German followers, the Naturphilosophen, took up his concept of archetypes, but not his belief in evolution. They regarded the archetypes not, as he did, as ancestral forms out of which the homologue organs had evolved, but as patterns of divine design -- leitmotivs which, together with all their possible variations, have coexisted since the day of Creation. Much the same beliefs were shared by some great anatomists in Europe at that time, among them Richard Owen. It was Owen who defined 'homologous organs' as 'the same organ in different animals under every variety of form and function'. While he tirelessly demonstrated the multitude of such organs in the animal kingdom, he attributed them to the parsimony of the divine Designer -- just as Kepler had attributed his planetary laws to the ingenuity of the divine Mathematician.
But whatever the beliefs of these men, the concept of homology came to stay, and became a cornerstone of modern evolutionary theory. Animals and plants are made out of homologous organelles like the mitochondria, homologous organs like gills and lungs, homologous limbs such as arms and wings. They are the stable holons in the evolutionary flux. The phenomena of homology implied in fact the hierarchic principle in phylogeny as well as in ontogeny. But the point was never made explicit, and the principles of hierarchic order hardly received a cursory glance. This may be the reason why the inherent contradictions of the orthodox theory could pass so long unnoticed.
The Law of Balance
There are manifestations on still higher levels of what I have called the stability of evolutionary holons. Such are the geometrical relations discovered by d'Arcy Thompson, which demonstrate that one species may become transformed i
nto another and yet preserve its own basic design. The drawings below show a porcupine fish (Diodon) and the very different looking sun fish (Orthogoriscus) as they appear in Thompson's classic, On Growth and Form, published in 1917.
I have compared the evolution of homologue organs to the procedure of motor-car manufacturers when they bring out a new model, which differs from the previous one merely in some modifications of this or that component, while the other standardised parts remain unaltered. In the case of the fish, it is not a particular organ that has been modified, but the chassis and body-line as a whole. Yet it has not been arbitrarily re-designed. The pattern has remained the same. It has merely been evenly distorted according to a simple mathematical equation. Imagine the drawing of the porcupine fish and its lattice of Cartesian co-ordinates imprinted on a rubber sheet. The sheet is thicker at the head end, and therefore more resistant than at the tail end. Now you grip the top and bottom edges of the rubber sheet and stretch it. The result will be the sun fish. Corresponding points of the anatomy of the two fishes will have the same co-ordinates (the eye, for instance, will have 'longitude' 0,5, and 'latitude' C).
Thompson found that this phenomenon had general validity. Putting the outline drawing of an animal on a grid of co-ordinates, and then drawing another animal belonging to the same zoological group, he found that he could transform one shape into the other by some simple trick of rubber-sheet-geometry, which can be expressed by a mathematical formula. The next drawing, Figure 8, shows the transformation, by means of a harmoniously deformed grid of Cartesian co-ordinates, of a baboon's skull into a chimpanzee's and a man's.
These are not idle mathematical games. They provide a realistic insight into the evolutionary workshop. Here are d'Arcy Thompson's own comments:
We know beforehand that the main difference between the human and the Simian types depends upon the enlargement or expansion of the brain and brain case in man, and the relative diminution or enfeeblement of his jaws. Together with these changes, the facial angle increases from an oblique angle to nearly a right angle in man, and the configuration of every constituent bone of the face and skull undergoes an alteration. We do not know to begin with, and we are not shewn by the ordinary methods of comparison, how far these various changes form part of one harmonious and congruent transformation, or whether we are to look, for instance, upon the changes undergone by the frontal, the occipital, the maxilliary and the mandibular regions as a congeries of separate modifications or independent variables. But as soon as we have marked out a number of points in the gorilla's or chimpanzee's skull, corresponding with those which our co-ordinate network intersected in the human skull, we find that these corresponding points may be at once linked up by smoothly curved lines of intersection, which form a new system of co-ordinates and constitute a simple 'projection'* of our human skull . . . and in short it becomes at once manifest that the modifications of jaws, brain-case, and the regions between, are all portions of one continuous and integral process. [10] * In the sense of Projective Geometry.
Surely this process is the exact opposite of evolution through random changes 'in all and every direction'. If that were the case we should get what Thompson calls 'a congeries of separate modifications or independent variables'. In fact, the variations are inter-dependent, and must be controlled from the apex of the hierarchy which co-ordinates the pattern of the whole by harmonising the relative growth-rates of the various parts.
Thus the rapid expansion of the anthropoid brain was accompanied by appropriate changes in the other parts of the skull, effected by a simple and elegant geometrical tramformation. The eighteenth century was familiar with this kind of phenomenon, which the twentieth took a long time to re-discover. Goethe called it 'Nature's budgeting law', Geoffroy St. Hilaire called it loi du balancement, the principle of the equilibrium of organs. From the concept of developmental homeostasis there is only one logical step to the concept of evolutionary homeostasis -- the loi du balancement applied to phylogenetic changes. Faithful to Goethe, one might call it the preservation of certain basic, archetypal designs through all changes, combined with the striving towards their optimal realisation in response to adaptive pressures.
The Doppelgängers
The last phenomenon to be mentioned in this context is an enigma wrapped in a puzzle. The enigma concerns the marsupials -- the class of pouched animals living in Australia. The puzzle is that evolutionists refuse to see the enigma.
Nearly all mammalians are either marsupials or placentaIs. (The 'nearly' refers to the near-extinct monotremes, such as the duck-billed platypus, a kind of living fossil which lays eggs as reptiles do, but suckles its young.) The marsupials could be called the poor relatives of us 'normal', that is, placental, mammals; they have evolved along a parallel branch of the evolutionary tree. The marsupial embryo, while in the womb, receives hardly any nourishment from its mother. It is born in a very immature state of development, and is reared in an elastic pouch, or bag of skin, on the mother's belly. A newborn kangaroo is really a half-finished job -- about an inch long, naked, blind, with hind-legs that are no more than embryonic buds. One might speculate whether the human infant, more developed but still helpless at birth, would be better off in a maternal pouch than in a cot; and also whether this would increase its oedipal inclinations. But whether the marsupial's method of reproduction is better or worse than the placental's, the point is that it is fundamentally different.
The two lines split up at the very beginning of mammalian evolution, in the Age of Reptiles, and have evolved separately, out of some small mouse-like common ancestral creature, over some hundred and fifty million years. The enigma is, why so many species produced by the independent evolutionary line of the marsupials are so startlingly similar to placentaIs. It is almost as if two artists who had never met, never heard of each other, and never had the same model, had painted a parallel series of nearly identical portraits. Figure 9 shows on the left side a series of placental mammals, and on the right their opposite numbers among marsupials.
A. Marsupial jerboa and placental jerboa. B. Marsupial flying phalanger and placental flying squirrel (after Hardy). C. Skull of marsupial Tasmanian wolf compared to skull of placental wolf (after Hardy).
Let me repeat: we know that, contrary to all appearances, the two series of animals have evolved independently from each other. Australia was cut off from the Asiatic mainland some time during the late Cretaceous, when the only existing mammals were unpromising-looking tiny creatures, hanging precariously on to existence. The marsupials seem to have evolved earlier than the placentaIs from a common egg-laying ancestor with part-reptilian, part-mammalian features; at any rate, the marsupials got to Australia before it was cut off, and the placentals did not. These immigrants were, as already said, mouse-like creatures, probably not unlike the still surviving, yellow-footed pouched mouse, but much more primitive. And yet these mice, confined to their island continent, branched out and gave rise to pouched versions of moles, ant-eaters, flying squirrels, cats and wolves -- each like a somewhat clumsy copy of the corresponding placentals.* Why, if evolution were a free-for-all, restrained only by selection for fitness, why did Australia not produce some of the bug-eyed monsters of science fiction? The only moderately unorthodox creation of that isolated island in a hundred million years are the kangaroos and wallabies; the rest of its fauna consists of rather poor replicas of more efficient placental types -- variations on a limited number of archetypal themes. **
* Marsupials have also evolved, again independently, in South America. ** The reasons for the inferiority of marsupials compared to placentals will be discussed in Chapter XVI.
How is the enigma to be explained? The explanation offered by the orthodox theory is summed up in the following passage from an otherwise excellent textbook, that I have repeatedly quoted: 'Tasmanian [i.e., marsupial] and true wolves are both running predators, preying on other animals of about the same size and habits. Adaptive similarity [i.e., adaptation to similar envir
onments] involves similarity also of structure and function. The mechanism of such evolution is natural selection.' [11] And G.G. Simpson, a leading Harvard authority, discussing the same problem, concludes that the explanation is 'selection of random mutations'. [12]
Once more the deus ex machina. Are we really to believe that the condition described by the vague terms 'preying on animals of approximately the same size and habits' -- which could be applied to hundreds of different species -- sufficiently explains the emergence, twice over, independently from each other, of the almost identical two skulls in Figure 9? One might as well say, with the wisdom of hindsight, that there is only one way of making a wolf, which is to make it look like a wolf.
The Thirty-six Plots
In Chapter VI, I compared the series of scanning and filtering mechanisms through which the intake of our sense-organs must pass before it is admitted to awareness and found worthy to be preserved by memory, to the seventeen gates of the Kremlin. The sense-receptors of eye, ear and skin are exposed (in a famous phrase of William James') to a continuous bombardment by the 'blooming, buzzing confusion' of the outside world; without careful scrutiny by the sentries guarding the gates, we should be at the mercy of all random intruders, and our minds and memories would be all confusion, unable to make sense of our chaotic sensations.
We can now apply the same metaphor to the alert guardians who protect the gates of heredity against the chaos that would ensue if random mutations 'in all and every direction' were given free access. We must assume that mutations -- that is, 'changes' in the original sense of the word -- on the elementary quantum level are occurring constantly under the impact of radiations and other factors impinging on the gene-complex. The giant molecules of the chromosome chains consisting of millions of atoms must also be surrounded by a 'blooming, buzzing confusion' of their own sub-microscopic universe. Most of these changes would be transitory, quickly rectified by self-regulatory devices of the gene-complex, or without noticeable effect on its functioning. The relatively few mutations potentially capable of affecting heredity would be submitted to sifting and processing at the gates of successively higher levels of the hierarchy. I have mentioned several stages of this processing, for which there is solid evidence: the elimination of 'mis-spelt' syllables in the genetic code; 'developmental homeostasis' which ensures that mutations should affect a whole organ in a harmonious way; similar processes on higher levels (Thompson's transformations, loi du balancement) which preserve the proper equilibrium between organs; the evolution of homologous organs from different combinations of genes (drosophila-eye), and of similar species of independent evolutionary origin (marsupials).*