Chapter 3: From Potentiality to Realization in Evolutiony by Theodosius Dobzhansky
Theodosius Dobzhansky, after teaching for many years at Columbia University, finished his career by teaching in the Department of Genetics at the University of California at Davis. He died in 1975.
The universe is the product of the evolutionary process. All that was, is, and will be has evolved, is evolving, and will evolve. The inorganic and human evolutions are parts of a single process. Ultimately all evolution is one. It is reasonable to assume that the past evolution has brought about the present, and the present will lay the foundation for the realization of future evolution. If so, the potentialities of the future must have been present in the past. The Big Bang, or whatever it was that launched the development of the Cosmos, contained the potentiality of life, and hence of the biological evolution. The primordial life had the potentiality of evolving mankind, as well as every one of the several million existing and extinct species. Mankind, the human species, is unique in several ways. It has rationality, self-awareness, and death awareness. These and other unique properties of the human species must have been among the potentialities of the primordial life and the primordial cosmic substratum.
The statement that the potentiality of man was contained in the primeval living monad and in the primordial cosmic stuff may seem inordinately audacious. More careful consideration shows that it is really trite. It means no more and no less than that the process of evolution has in fact generated life and engendered man; these are patently true but trivial affirmations! It does not necessarily follow from these affirmations that all matter or all energy have in them some bits of life or protolife, or that the primordial amoeba or the primordial virus possessed some rudiments of human consciousness or some embryonic minds. To have a potentiality to become something does not mean possession of a snippet of that something. Between potentiality and realization there intervenes a process of development or evolution. It is worthwhile to consider at this point some biological illustrations. Animals evolved quite different kinds of organs of respiration -- lungs, gills, tracheae, etc. The ancestral unicellular and primitive multicellular organisms respire through the entire body surface. It is gratuitous to ascribe to them proto-lungs, proto-gills, and proto-treachae. Mammals and birds arose from reptiles, reptiles from amphibians, amphibians from fish. Yet there is no trace of communication by learned symbolic languages among reptiles, of hair or feathers among amphibians, of the auditory apparatus of land vertebrates, or of legs or wings, among the fish. A zoologist can, to be sure, identify the body parts in the ancestral groups that gave rise to new organs and functions in the derived classes. However, it scarcely makes sense to say that certain bones of a fish skull are incipient ears, or that two pairs of fins in fish have concealed in them the five-fingered appendages of the higher vertebrates. Biological and human evolution are creative processes. This means that they at least occasionally engender novelties. How do novelties arise?
Preformation, Epigenesis, and Creativity
In classical biological terminology, a development may be preformistic or epigenetic. Preformation postulates that the germ has in it a miniature copy of the new organism, or at least of its main. components. Preformistic development is essentially growth. A human sex cell was imagined to contain a miniature homunculus, which increases in size until it becomes an embryo, an infant, and eventually an adult woman or man. Evolution may conceivably also be preformed. Etymologically, evolution means unfolding or unrolling something that had been present in the ancestral forms or substances. Organisms that evolved were latent but somehow prefigured in ancestral organisms. Evolution was, then, no more than gradual removal of masks and camouflages; a homunculus was hidden in the ancestral amoeba, and then it gradually became open to view.
Epigenesis means the development of something that did not exist previously. Epigenetic evolution is a creative process. To my taste, preformation is less interesting, and I am tempted to say less inspiring, than epigenesis. Being interesting and inspiring is however not a criterion of validity of a scientific or philosophical theory. The theories of preformation and epigenesis must be examined further. First of all, epigenesis does not mean creation ex nihilo. A fertilized human egg cell does not contain a homunculus, but neither is it a structureless drop of viscous liquid. It contains, in addition to nutrient materials, a developmental program encoded in the DNA of the chromosomes. The outcome of the development is, in a given environment, predetermined by this program.
Did the primordial life contain a program of evolutionary developments? Some philosophers and some biologists thought that it did. This led to evolutionary theories called orthogenesis, nomogenesis, finalism, etc. These theories, now mostly abandoned, postulated that the ancestral organisms were programmed to evolve into everything into which they did evolve. But this is failing to perceive the basic difference between the individual and the evolutionary developments (ontogeny vs. phylogeny). The ontogeny is so programmed that it either yields an individual of a certain species or nothing. Even so, the programming is not absolutely rigid; in different environments the development proceeds in more or less subtle or even clearly diverse ways. Thus, the human development depends, to use somewhat antiquated words, both on nature and on nurture. Evolution is not programmed in the same way as is ontogeny; in fact it lacks a program. This does not mean that the phylogeny is wholly unconstrained or wholly at the mercy of the environments. A mouse is unlikely to evolve into a species of elephants, or an elephant into a mouse. Their organizations are so radically distinct that they could hardly be reconstructed in such ways, even if this were advantageous in some environments. On the other hand, an environmental challenge may be answered by an adaptive modification. ‘May’ rather than ‘must,’ because this depends on many factors, such as the availability of genetic variance on which natural selection can work. Biological and human evolutions come neither from within the organism nor from the environment. They involve creative syntheses of internal and external causes.
Determinism or Freedom?
How much determinism or indeterminism is there in evolution? Was evolution fated from the beginning to produce mankind and every other species? Does evolution sometimes involve origination of radical novelties? Much confusion has entangled these problems, and I can hardly hope to disentangle them all here. The physicist and cosmologist Laplace believed that to an all-knowing intelligence "nothing would be uncertain, the future as well as the past would be present to its eyes." The Laplacean ‘hard’ determinism is now out of fashion even in physics. The universe is one, and it has evolved only once. Evolution is a unique event, or rather a unique concatenation of events. Since evolution is not acausal, the meaning of Laplacean determinism is at most that what happened was bound to happen. Even this is questioned by process philosophers. Anywhy, it does not follow that if the evolution were to start again it would go exactly as it did before.
The problem of evolutionary determinism is often brought up in relation to the hypothetical extraterrestrial life on hypothetical planets in other solar systems. The problem is not meaningless, but inferences that one may put forward are not at present verifiable or falsifiable. The crucial consideration is that if the hypothetical planets actually exist, none of them can be at any single moment identical in the states of every component with the earth as it was at any point of its history. The Laplacean determinism is therefore beside the point, and the problem is shifted back from astronomy and chemistry to evolutionary biology. The question to be asked is this: is the evolutionary process at all likely to be repeated even in its most general features on planets with similar, though not identical, environments? Those who ventured to speculate about these matters came to diverse decisions. A majority, composed mainly of cosmologists, physicists, chemists, and a few biologists, surmised that the extraterrestrial evolutions should proceed as the earthly one did, including the production of ‘humanoids,’ i.e., of rational beings. Projects are discussed in all seriousness of establishing radio communications with these ‘humanoids’ in other solar systems and even other galaxies. Such projects fit the needs for romance and fancy, felt by many millions of people who are bored with everyday drudgery.
A minority of skeptics, most of them biologists, see themselves obliged to deflate the romantic bubble. Assume for the sake of argument that extraterrestrial life exists, and that it is based on proteins and DNA like the life on earth with which we are familiar. Even so, that extraterrestrial life would evolve in some ways quite dissimilar to the earthly one. The probability of repetition of terrestrial evolution is zero. The same holds for the possibility that, if most life on earth were destroyed, the evolution would start anew from some few primitive survivors. That evolution would be most unlikely to give rise to new man-like beings. I want to make it perfectly clear that the un-repeatability of evolution does not mean that evolution is acausal. Nor is evolution, as sometimes alleged, due to ‘pure chance.’ Evolution, at least on the biological and the human levels, is neither rigidly predestined nor completely indeterminate. Viewed in the perspective of time, evolution is a creative process. It has so multiple a causation that its outcomes are unlikely to be repetitious. Each evolutionary event is conditioned by the whole preceding history of the species, by the environment in which it occurs, and possibly, in higher organisms with developed nervous systems, by the behavioral reactions of these organisms.
Emergence of Novelty
We have postulated that the potentiality of every evolutionary event was present in the primordial life and the primordial cosmic stuff. The problem then turns out to be what is involved in the realization of potentialities. According to the preformation model, evolution is mostly growth or unwrapping. The primordial life carried rudiments of every basic structure and function that appeared later. It may have had protopsychism, and protovoluntarism, and protogood, and protoevil. Metaphysics of panpsychism or panvitalism are attractive perhaps for the same reasons which make all preformistic notions attractive to many. Everything is in existence from eternity, albeit only in hidden states, which need germinate, sprout and grow. Old-fashioned vitalists supposed that the origin of life involved the addition of a vital force, which came from some unspecified place, or perhaps from God. Panvitalism avoids this problem by postulating that life was also preformed in lifeless matter. Panvitalism and panpsychism make it unnecessary to assume that a vital force need be added from somewhere. It was invisibly present everywhere before there was life.
Some of the process philosophers have, to my surprise, rejected the identification of panvitalism and panpsychism with preformation doctrines. Yet to a biologist, preformation is a perfectly respectable biological and evolutionary view, even though it is at present a minority view among embryologists and evolutionists. If you postulate that life and mind were brand new principles which began to appear at some time and were not at all present earlier, you have an epigenetic evolutionary view; if, by contrast, you find the rudiments present in all nature universally, this is a preformistic view. It must be admitted that epigenetic models lead to difficulties, because they postulate the emergence of qualities, such as life and mind, in evolving systems which did not possess them at all. Origination of novelty is harder to envisage than mere growth.
Epigenesis does not assume anything arising ex nihilo. My body is composed of atoms of the same chemical elements which are found in inorganic matter. But in my body these atoms are components of many kinds of molecules which are formed chiefly or only in organisms. Moreover these molecules are not mixed uniformly in a solution -- they are arranged in unbelievably complex patterns known as cells. And the cells, in turn, are ordered in an even more complex pattern, which is my body. Other, rather similar but not identical patterns are individuals of the species Homo sapiens, a great multitude of less similar patterns are representatives of other animal and plant species. Evolution is emergence of new patterns, particularly on the cellular and organismic levels. Living beings as we observe them now are patterns of inorganic and organic constituents. These patterns emerged and were gradually perfected during at least three billion years of biological evolution on earth. We should never forget about these billions of years of evolution. A sudden appearance of life from no life, and of mind from no mind, would be, in the words of Sewall Wright, ‘sheer magic.’ The billions of years of evolution have made this ‘magic’ everyday occurrence. Indeed, the kindling of new life in the process of reproduction of organisms would be awe-inspiring, if it were not so commonplace that it is taken for granted.
Molecular constituents of all organisms are far more similar than the organisms themselves. It is remarkable that the same four kinds of nucleotides compose the DNA’s of all organisms. Equally remarkable is that the same twenty kinds of amino acids make up most proteins, in organisms all the way from bacteria and viruses to man. Evolution was the emergence of patterns more often than invention of new chemical components. Life and mind did not arise ex nihilo. They appeared in the process of evolution as novel patterns, and patterns of patterns, of organic functions. Evolution involved what one may refer to as emergence or transcendence. These words nettle many scientific puritans. The dictionary definition of ‘transcendence’ is, however, simple: "going beyond ordinary limits, surpassing, exceeding." There is no doubt that this happened in evolution -- cosmic evolution transcended itself producing life, and biological evolution did so when there emerged mind.
Realized and Unrealized Evolutionary Potentialities
At the present state of our knowledge, it seems most probable that all life on earth was monophyletic at its origin, i.e., derived from a single kind of primordial life. If this is true, the primeval life had potentialities of originating every one of the existing and fossil species of organisms. It seems to me that this makes the preformationist model unlikely. Far too many things would have to be preformed! As already pointed out above, organic evolution is not what the etymology of the word ‘evolution’ suggests, i.e., not unfoldment of what was there hidden to begin with. Evolution has involved multiple branching and divergence of countless evolutionary lines. The old idea of the ‘great chain of being’ implied that all organisms can be ordered in a single sequence, from primitive to complex. This idea was important in the history of biology, since it suggested the idea of evolution. But as far as I know, the ‘great chain’ idea has no adherents at present. Instead of a single chain, evolution proceeded along innumerable branching lines, most of them ending blindly in extinction. Starting from a single original source, the evolutionary lines have branched and rebranched, and this branching has led to increasing structural and functional complexity. Evolutionary progress, no matter how the concept of progress may be defined (and no generally accepted definition has yet appeared), has undoubtedly occurred in some lines, but in other lines there has been stasis or even partial regression.
Potentialities of all biological evolution were present in the primordial life. This must now be supplemented by the assertion that, in addition to all the potentialities that became realized, the living world had, and doubtless still has, countless unrealized potentialities. The foundations on which this assertion rests are really very simple. So great is the efficiency of the Mendelian mechanism of gene recombination that only a minuscule fraction of the potentially possible gene combinations can ever be realized. This was pointed out by Sewall Wright already in 1932. Supposing that a species has only 1000 genes each in ten different allelic forms (both figures are overly conservative estimates), 101000 gene combinations are potentially possible. The number of subatomic particles in the Universe is estimated by physicists to be of the order of only 1078. Even if most of the possible gene combinations are poorly viable, or inviable, a stupendous majority of the genetic potentialities of the living world have never appeared, and never will be realized and tried out by natural selection.
There is no way of telling what sorts of organisms evolution could have produced but did not in fact produce. There is plenty of evidence that the availability of an opportunity for a certain way of life does not by any means guarantee that species of organism exploiting that opportunity will evolve. This is interesting to philosophers who wish to discover the degree of determinism in evolution. Biologists have, since pre-evolutionary days, been fascinated by instances of structural parallelisms in not closely related animals and plants that exploit similar environments in similar ways. Whales and dolphins resemble fishes in body shape, though not in internal anatomy and physiology. Cacti in the deserts of the New World are mimicked by euphorbias in African deserts, although they are botanically not closely related. Marsupials have evolved in Australia several forms which occupy ecological niches held on other continents by placental mammals -- wolf-like, squirrel-like, mole-like, woodchuck-like, etc.
Biologists have paid much less attention to the equally significant but opposite phenomena -- absence of evolutionary parallelisms where they could, by analogy, be expected. Thus, there are no horse-like, deer-like, or antelope-like marsupials in Australia. The large herbivores in Australia are instead kangaroos, which are obviously quite different from horses or antelopes. And yet in South America there developed in Miocene times horse-like and camel-like animals; these belonged to the extinct order of mammals, Litopterna, and were not closely related to the real horses and camels. One of the most widespread and ecologically obviously successful groups of ants in the American tropics are the fungus-growing Atta. These agriculturalists of the insect world feed exclusively on certain kinds of fungi which they cultivate in subterranean ‘gardens’ on especially collected pieces of leaves and other plant parts. Yet such agriculturalist ants are wholly missing in the Old World tropics. Their ecological success and diversity in the New World virtually insures that they could flourish in the Old World as well if they evolved or were introduced there. The absence in the Old World of humming birds is a further example of lack of evolutionary parallelism where it could well be expected.
The Uniqueness of Mind
The possession of human mind makes our species a unique product of an evolutionary transcendence. The capacities for abstract reasoning, symbolic language, self- and death-awareness set mankind apart from the rest of the biological world. Was a man-like ‘rational’ species predetermined to appear in the course of evolution? Some philosophers and biologists thought so; in fact, the so-called finalists contended that organic evolution as a whole was designed to bring man into existence. Or was the origin of man a matter of chance alone, a haphazard outcome of the operation of the evolutionary roulette? This view also has its exponents, among whom perhaps the most recent and distinguished is Jacques Monod. His statement is crystal clear: "man knows at last that he is alone in the universe’s unfeeling immensity, out of which he emerged only by chance." I believe that the emergence of mankind, and for that matter of any other form of life, was neither foreordained nor due to random chance. Mankind is a masterpiece of creative evolution. Like the creativity of a human artist, evolutionary creativity is a synthesis of environmental challenges with the available biological (or intellectual) means to respond to these challenges.
Julian Huxley defined evolution as a process which generates, among other things " . . . more complex organizations, higher levels of awareness, and increasingly conscious mental activity." Teilhard de Chardin postulated the so-called law of complexity-consciousness, according to which mind must inevitably emerge when a certain level of structural and functional complexity is reached. As a definition of evolution, that given by Huxley is certainly invalid, since increasing complexity, awareness, and mental activity occur by no means in all, not even in a majority, of evolutionary lineages. In many lineages the opposite has occurred, and the self-awareness and ‘mental activity’ appeared in only a single species, among two or more millions that now exist. We need not take a stand here on the problem whether some rudiments of mind, or self-awareness, or conscious mental activity, are present in animals other than man. Most of the observations bearing on this problem come from introspection rather than from controlled experiments. As a result, competent students of the issue hold quite different opinions, none of which is demonstrably right or wrong. An evolutionist is not surprised if he finds component parts or precursors of organs or functions fully developed in more complex organisms in their less complex relatives. Human mental abilities must have emerged in evolution from raw materials that were present on prehuman levels. Anyway, the human psyche is unique in the living world. This uniqueness does not force us to return to the Cartesian body-soul dualism. It does however illustrate that evolution can produce radical novelties.
There is no reason to think that, given some millions or tens of millions of years to evolve further, other animal species will evolve humanoid minds. Nor is it likely that if mankind were to become extinct it would be replaced by another ‘rational’ or ‘humanoid’ species. The fact that mind has emerged only once in the whole known course of evolution does not, in my opinion, bear out the view that rudiments of mind, or some kind of protominds, are omnipresent or even widespread in the living world. One can see that certain conditions are necessary, but evidently not sufficient, for the appearance of a psyche capable of self-awareness. A highly developed nervous system and a capacious brain appear to be indispensable for the emergence of anything like human mind. Jelly-fishes, ants, termites, and even birds have not evolved nervous systems that could sustain humanoid performance. As stated above, there is no assurance, and even not much likelihood, that given some more millions of years to evolve, any of them would reach a level of brain development at which the emergence of mind would be a possibility. This may seem, particularly to non-biologists, excessive skepticism; at least a brief explanation of my reasons for this stand seems in order.
Any biologist, at any rate any not exclusively laboratory biologist, knows that organisms that inhabit a given geographic area exploit its resources in many different ways. Yet all of them possess adaptedness to their environments and their ways of life, for otherwise they would have died out. Already Darwin had to rebut the objection to his theory that the coexistence at our time level of high and low, primitive and advanced organisms contradicts the doctrine of evolution. If, for example, mammals are more advanced than amoebae, and flowering plants more than bacteria, why then are amoebae, bacteria, and a host of other ‘primitive’ organisms still with us? Why have they not evolved to more advanced grades? The answer is that bacteria and amoebae exploit different environments or sub-environments, or exploit them in ways different from, for example, insects or birds or mammals. There is no ‘law’ that would make all organisms evolve just for the sake of evolving. Evolution propelled by natural selection is sometimes progressive, but not always and not necessarily so. Evolution is thoroughly opportunistic. Bacteria and amoebae seem to be doing as well in their ecological niches as insects and vertebrates in theirs.
Life appeared in the universe some billions of years after its origin in the hypothetical ‘Big Bang.’ Furthermore, it appeared, as far as anybody knows for certain, on just one of the myriad of celestial bodies, the earth. Before that event, the universe was lifeless, and most of it is still lifeless. Some three billion years after the origin of life on earth, there appeared man. During these billions of years life existed without man, and could continue to exist without him, in some ways even better than with him, since man is a pitiless destroyer of many animal and plant species. Yet man did arise and develop a completely novel and hitherto unprecedented way of life.
Mankind adapts its environments to its genes more often than it changes its genes to fit its environments. The rationality, or mind, or symbolic communication, or self-awareness -- call the evolutionary uniqueness of man by whatever name you prefer -- has made him by far the most successful biological species. His arrogance makes him sometimes call himself the Lord of Creation. The origin of man was neither predestined nor was it an evolutionary accident. Mankind’s novel and unique psychic capabilities came about as a result of a long travail of evolutionary creation. The successful outcome of this travail was not guaranteed. There were two species of Australopithecus living in late Pliocene and early Pleistocene periods -- A. africanus and A. robustus. The A. africanus was apparently our ancestor; it did evolve the biologically unique human qualities, and its descendants gradually became human. The A. robustus did not so evolve, and eventually became extinct. Now both species must have descended from some common, but as yet unknown, ancestral species. This ancestor must have had potentialities of becoming humanized. The potentialities became realized in one species derived from it, but not in the other species.
Life at its origin was a radical novelty in the formerly lifeless world. Human mind was another radical novelty. Man, a species endowed with mind, or consciousness, or self-awareness -- call this unique property by whatever name you choose -- arose from ancestors not endowed with this property. To some philosophers the origin of such novelties is as unbelievable as magic. I can offer two considerations which will make this ‘magic’ perhaps less magical. In the first place, the evolutionary transcendence from the non-living to the living did not require anything like old-fashioned ‘vital force’ suddenly implanted by the Creator. Nor was the transcendence from the non-human due to implantation of a ‘soul.’ Both transcendences were basically like other evolutionary transformations, albeit more radical ones.
In the second place, the transcendences should not be imagined to have been sudden. They took probably millions of years. The transitions from no life to life, and from no mind to mind, were gradual. Our scientific knowledge is, of course, quite insufficient to give anything like satisfactory accounts of these transitions. Biologists as basically different in their philosophical and biological views as W. H. Thorpe and Jacques Monod agree that the origin of life is a difficult, and thus far intractable and unsolved, problem. I concur. However, probably thousands of biologists and biochemists all over the world are now working on this problem. Their working hypothesis is that life arose epigenetically in a lifeless world. Assuming that life always existed is a simplification, but not a helpful simplification.
The origins of life and mind are indeed miraculous. Do not forget, however, that many other biological phenomena also strike us as wondrous and awesome. Consider the origin and development of mind in a human child. A miracle indeed! But no more miraculous than the origin of mind in human evolution. A newborn infant has a potentiality of developing mind, and self-awareness, but this potentiality can be realized only by way of a slow and gradual process of maturation. As pointed out above, a potentiality of mind must have been present in all ancestors of the human species, down to the primordial life. The analogy between the evolutionary origin and the maturation of mind in a growing child must not, to be sure, be pushed too far. Ontogenetic and phylogenetic potentialities are fundamentally different. Ontogeny is a product of phylogeny, not vice versa, as some people wrongly assumed. The alternative to realization of many ontogenetic potentialities is death; a child either grows up or dies. Not so with phylogenetic potentialities. In the first place, these potentialities are innumerable. Secondly, a great majority of the potentialities are never realized. Novelty may emerge or not emerge. This is not due to some intrinsic biological indeterminacy, but rather to an overwhelming complexity of very numerous interacting causal chains. You may see here a precursor of freedom on the human level.