VIVOS VOCO: J.B.S. Haldane (1892-1964)

Lysenko and Genetics

Published: Science and Society, vol. IV, No.4, 1940

Lysenko's contribution printed in the summer number of "Science and Society" will certainly "give occasion to the enemy to blaspheme." I have little doubt that he has gone too far in some directions, but it is important to see what there is of value in his criticism of orthodox genetics.

He begins by attacking the theory, which appears to be taught in the Soviet Union, that once a pure line is established, selection is useless. This theory is simply false, for the following reason. A pure line originally consists of individuals all of which are homozygous and genetically alike. But in course of time this ceases to be the case as a result of mutation, and also in the case of an allopolyploid such as wheat, of crossing over between chromosomes which do not normally cross over. Hence a pure line gradually breaks up into other approximately pure lines.

Some of these will be worse from an economic point of view than the original line. But some at any rate are better adapted to local conditions than their ancestors. Hence Lysenko is quite right in stressing the importance of selecting "elite strains of seed" from so-called pure lines. Any reader who supposes that I am taking this line because Lysenko is a Communist might do worse than read a paper which I published in the Journal of Genetics for 1936, entitled "The Amount of Heterozygosis to Be Expected in an Approximately Pure Line."

His next point, the breadth of the zone of isolation needed for different crops, has nothing to do with Mendelism as such. I have of course no means of judging who is right in this controversy, but I should be prepared to bet on Lysenko's being substantially correct.

Then we come to the question of the three-to-one ratio, which Lysenko says is a statistical, not a biological regularity. I confess that I am not quite clear what he means in this case, perhaps because his speech has been summarized. Where a three-to-one ratio is expected according to the laws of formal genetics, it is very rarely obtained with complete accuracy. The deviations from it are due to two causes. First of all, we have deviations due to chance. Thus if we expect 30 hairy and ten smooth plants we are quite likely to get 33 and seven or 27 and 13. And this fact is of great biological importance. If plants or animals were always produced in exactly Mendelian ratios there would be a perpetual equilibrium in hybrid populations. These deviations, so far as they are random, are partly due to sampling, partly to linkage of the gene studied with other genes in the same chromosome affecting viability or fertility. Owing to these chance deviations, one type or another will ultimately disappear from a small population, and it will become homogeneous. Sewall Wright of Chicago has studied this effect in great detail. Second, when large numbers are grown, a deviation from the three-to-one ratio is usually found, because one type is fitter than the other. One of the largest lists of such deviations in any plant was published by de Winton and myself *. If there were no systematic deviations of this kind there would be no natural selection based on survival of the fittest, even if there were reproductive selection based on differences of fertility. Thus systematic deviations from the three-to-one ratio are a fact of extreme biological importance.

* D. de Winton and J. B. S. Haldane, Journal of Genetics, XXIV, p. 1.

His next point, the importance of selection in the F₁, or first hybrid generation, is correct if the hybrids are not between pure lines. As we saw, pure lines are ideals which are rarely quite realized, and agricultural varieties may be very far from pure lines.

Next we have the question of food. I think that nine times out of ten Lysenko is wrong, that is to say that you cannot improve a breed of animals by improving its food. But there are cases where this is possible, and they may be common enough to make Lysenko's principle of great practical value. The clearest of such cases was discovered at Bar Harbor, Maine, by Little's group of workers on mouse genetics and has been specially studied by Bittner. For many years they had kept different pure lines of mice. Each line had a characteristic liability to mammary cancer in females. In one line 90 per cent of all females who did not die of some other cause before the age of two years would develop this disease, in another line only 5 per cent. The members of the immune line were no more likely to develop it if they were caged for months with the susceptible line. The liability seemed to be hereditary. But it turned out that if the young of the susceptible line were separated from their mothers at birth and suckled by immune females they were much less likely to become cancerous. And this partial immunity is handed on to their children.

Nothing of the kind has been discovered for other forms of cancer. And I believe it to be a rarer phenomenon than Lysenko supposes. But it is futile to deny its existence and to regard Lysenko's assertion of its possibility as in any way unscientific.

Now follows the question of grafting. Lysenko personally vouches for four cases where tomatoes have been altered by grafting. Tomatoes belong to the Solanaceae, which have long been known to be particularly susceptible to virus diseases. These diseases can be transmitted, among other methods, by grafting. Later research has shown that besides disease-producing viruses, it is possible to transmit viruses which have no obvious effect on the plant, but immunize it to one or more of the disease producers. Some of these viruses are known to be heavy proteins which reproduce (or are reproduced) within the plant cells. Lysenko claims to have evidence of transmissible agents which alter the shape of the fruit. It seems quite possible that the range of transmissible agents stretches from those which produce obviously pathological effects such as yellow patches on the leaves, to others which produce morphological effects like those of genes. Daniel and Dangeard in France have reported similar results in Compositae such as the Jerusalem artichoke.

On the other hand, I don't agree with Lysenko in believing that Michurin gave a white-fruited cherry red fruit by grafting it. There is a vast amount of practical experience in grafting cherries, apples, plums, loses, and other members of the Rosacene, and no recorded case of a permanent color change. Michurin's claims to have succeeded with hybridizations which otherwise failed, as a result of grafting, are on quite a different footing. They may or may not be confirmed by workers in other countries. But so little is known about the conditions for successful hybridization that they do not seem to be a priori improbable. And in view of the great value of Lysenko's technique of vernalization, which has been amply proved not, only in the Soviet Union but all over the civilized world, I should personally be surprised if his statements on results obtained by him were not largely correct.

But scientific pioneers are not infallible. Pasteur did more for the theory and practice of fermentation than any other man. Yet he made some big mistakes. Having discovered that the usual agents of fermentation, such as yeasts and bacteria, were alive, he denied the possibility of fermentation by nonliving substances. Yet today thousands of different enzymes are known, about twenty have even been crystallized by Sumner, Northrop, and others, mostly in the U.S.A. In the same way Lysenko, who is right in pointing out that the majority of characters showing Mendelian inheritance are of little economic importance, is quite wrong in supposing that none of them are.

I take a simple example from British agricultural practice. Two dominant sex-linked genes, for barred feathers and for silver as opposed to gold feathers, show up in newly hatched chicks. Thus by a suitable cross, for example of a Light Sussex hen and a Rhode Island Red rooster, we can get chickens whose sexes can be separated at once and given different food. So long as ten years ago a single British firm was raising 800,000 chicks a year from such crosses. This was done with severely practical motives, and not to confute Lysenko. If his authority prevents similar practice in the Soviet Union he will be doing a disservice to socialism.

In the same way, I am sure that he goes much too far in his attack on the chromosome theory. His statement that "any hereditary properties can be transmitted from one breed to another even without the immediate transmission of chromosomes" is, in my opinion, absolutely false, and I think that anyone with practical experience of grafting roses or apples would agree with me. But it is equally false to say that no hereditary properties can be so transmitted. The correct statement is as above, but substituting "some" for "any."

In the same way Lysenko was wrong if he referred to the theories of current genetics, such as the three-to-one ratio and the like, as "fantasies." They are not fantasies, but approximations. Copernicus's theory that the planets went round the sun in circles was an approximation. Kepler's theory that they moved in ellipses was a better approximation. The Newton-Laplace theory was yet a better- approximation, but it was still undialectical, as it did not allow for any real history of the solar system in the sense of irreversible change. Then Kant and George Darwin showed that the solar system had undergone and would undergo slow and irreversible changes through tidal friction, with not only the moon but most of the planets moving in slowly widening orbits. Various developments of the theory of relativity suggest other slow changes.

Although the Copernican and Newtonian systems were inadequate, they were great advances on the systems of Ptolemy, Kidinnu, and other earlier astronomers. And I think posterity will rank Mendel with Copernicus or Kepler, though hardly with Newton.

It must not be supposed that Lysenko stands alone in his criticism of formal genetics and his belief that breeds can be altered by feeding. Some of his views are shared, for example, by .J. L. Hammond of Cambridge, England. I think that he has gone too far, but he may well have done a service to Soviet genetics by making his more traditionally minded colleagues examine not only the theoretical foundations of their work, but its relation to agricultural practice.

In the same number of "Science and society" Polyakov criticizes my mathematical work. Probably his criticism refers mainly to that summarized in The Causes of Evolution in 1930. He says that it includes "no consideration of real biological interrelations." This is largely true, because a mathematical treatment of even the simplest evolutionary problems is difficult. One must begin with problems as abstract as the motion of two perfectly elastic billiard balls on a frictionless table. I had to begin, just as mathematical physicists had to begin, by leaving out factors of great practical importance. Wright, Fisher, and others have greatly improved my work by making it more concrete. But I have also done so myself.

For example, fifteen years ago I calculated the equilibrium which should result when the same gene was constantly being produced by mutation and destroyed by natural selection. The idea of an equilibrium was undialectical, like Copernicus's idea of planetary motion in perfect and invariable circles. But it gave results of the right order of magnitude. Then Fisher pointed out that in this case selection of modifying genes would cause slow evolutionary changes in the apparent equilibrium. Later I dealt with "real biological interrelations" and showed that in civilized human populations the relaxation of inbreeding in recent centuries had probably caused a sharp decrease in the frequency of recessive abnormalities such as amaurotic idiocy, albinism, and some types of blindness. In fact the motor bus, by breaking up inbred village communities, was a powerful eugenic agent. Here, if I am correct, I am getting down to "real biological interrelations." If I were a Newton or a Maxwell, I might have got to this point in one step. I might even have done so had I been a Marxist fifteen years ago, in which case I should have been very suspicious of equilibriums, knowing that the conflict between two tendencies such as mutation and selection may lead to apparent equilibrium, but is very apt to cause real changes, either slow evolutionary changes or qualitative leaps. I might also have been on the lookout for biological effects of technical changes in transport and communications.

I have also had to bring my theories up to date in the light of the new facts discovered in the Soviet Union by Dubinin and his colleagues in their studies of wild populations of Drosophila. I had predicted some of them, but by no means all. The fact that I had predicted some of them shows that my mathematics had a certain validity.

Any mathematical theory inevitably leaves out a good deal of relevant facts. But it is more exact than a theory expressed in words. And I believe that my own theories, inadequate as they doubtless are, were an essential step toward exact thinking in genetics.

Why I am a Materialist

Published in "Rationalist Annual", 1940

When I say that I am a materialist I mean that I believe in the following statements:

1. Events occur which are not perceived by any mind.
2. There were unperceived events before there were any minds.

And I also believe, though this is not a necessary logical deduction from the former two, that:

3. When a man has died he is dead.

Further, I think that it is desirable that other people should believe these statements. I do not mean that I believe that the universe is a machine, or that I am a machine; nor yet that consciousness does not exist, or has a lesser reality (whatever that means) than matter. When I say "I believe" I do not mean the word in the sense in which a fervent Christian uses it concerning the Virgin Mary, Pontius Pilate, and others who figure in the creeds. I mean it in the ordinary sense, in which, for example, I believe that dinner will be waiting when I go home, though, of course, the cook may go on strike or the chimney may catch fire. That is to say, I act, and propose to act, on the basis that materialism is true. But I am prepared to consider evidence to the contrary. And I certainly don't get shocked or angry if someone criticizes or doubts the truth of materialism.

Now the word "materialism" is used, particularly in controversy, to imply a belief that a good dinner is better than a good deed. In fact, a materialist is supposed to be a man who has, or does his best to have, large meals, a large mistress, a large bank balance, a large motor-car, and so on. It is not obvious why this should be so. Other peoples' meals are as material as mine, and a bank balance is not something tangible, like a cellar full of gold and jewels.

In practice I have found that professed materialists are generally less selfish than professed idealists. For idealism is a remarkably useful device to enable us to bear other peoples' ills, and particularly their poverty. It is easy to persuade ourselves that the poor have various spiritual blessings. But it is not so easy, when one's own affairs are concerned, to avoid the attitude of the idealist of whom it was written:

There was a faith-healer of Deal
Who said: "Although pain isn't real,
When I sit on a pin and it punctures my skin
I dislike what I fancy I feel."

I do not of course deny that some idealists are excellent people, and some materialists coarse and selfish. But on the whole I think the contrary is true, for reasons which will appear later.

Fifteen years ago I was a materialist in practice, but not in theory. I treated myself as a material system. We all do this to some extent. When we want to go somewhere we get into a train or bus, confident that on the one hand we shall not be able to propel ourselves so rapidly through space by the mere exercise of our wills, nor on the other that the vehicle will find any more difficulty in moving us than if we were a sack of potatoes. However, though we all have considerable faith in the applicability to ourselves of the laws of physics, our faith does not apply to chemistry. We should be willing to trust our weight to a rope which has been tested to stand double our weight, but we should mostly hesitate to drink half the fatal dose of a poison. Rightly too in some cases, for poisons in sub-lethal doses may do a good deal of harm. But not by any means always. Some poisons, such as carbon monoxide, are completely harmless in half the lethal quantity.

I applied the laws of chemistry to myself. For example, I said: "If a dog is given hydrochloric acid to drink (diluted, of course, so as not to injure its stomach), it excretes part of the acid combined with ammonia as ammonium chloride. Now men work in a similar way to dogs, and both are systems of partially reversible chemical reactions. So if I eat ammonium chloride I shall become more acid."

This did in fact happen. I was quite correct in my reasoning, or at any rate it led to a correct result.

However, although I was a materialist in the laboratory, I was a rather vague sort of idealist outside, for the following reason. I had learned that matter had certain properties. It consisted of atoms which united in particular patterns. They moved in definite paths under given forces, and so on. My belief in these theories was not a matter of mere docility either. I had tested them and risked my life on their substantial accuracy. Clearly, if matter had the properties attributed to it by physicists and chemists, something more was needed to account for living organisms. And it was far harder to account for mind.

As a believer in evolution I had to reject such theories as T.H. Huxley's epi-phenomenalism, according to which mind is a secondary consequence of a small class of material events (namely, those which go on inside our heads), but does not influence them. Apart from my very strong belief that I can act, the evolution of something as complicated as my mind, yet absolutely functionless, seemed most unlikely. Not that functionless organs are never evolved. On the contrary, it is probable that most organs are evolved in a rudimentary form before they develop a function. And I have not enough faith in the theories of Paley and his like to believe that every organ - for example, a cock's comb, a pigeon's cere', or a cassowary's wattle - has a function. However, I cannot believe that a system so complicated, and within its limitations so efficient, as the human mind could have evolved if it were functionless.

Nor did I see how, on a materialist basis, knowledge or thought was possible. The light which reaches my eyes causes nervous impulses in about half-a-million fibres running to my brain, and there gives rise to sensation. But how can the sensation be anything like a reality composed of atoms! And, even if it is so, what guarantee have I that my thoughts are logical! They depend on physical and chemical processes going on in my brain, and doubtless obey physical and chemical laws, if materialism is true. So I was compelled, rather reluctantly, to fall back on some kind of idealistic explanation, according to which mind (or something like mind) was prior to matter, and what we call matter was really of the nature of mind, or at least of sensation. I was, however, too painfully conscious of the weakness in every idealistic philosophy to embrace any of them, and I was quite aware that in practice I often acted as a materialist.

The books which solved my difficulties were Frederick Engels's Feuerbach and Anti-Duhring, and later on V.I. Lenin's Materialism and Empirio-Criticism. But the actual progress of scientific research in the last fifteen years also helped me enormously. None of the books which I have mentioned is easy if one has been brought up in the academic tradition which goes back to Plato and Aristotle. This is partly because they apply scientific method not only to philosophy but to philosophers. They are not merely concerned with showing that their authors are right and their opponents wrong but with explaining why, under particular social conditions, such and such theories are likely to gain wide acceptance. Hence, unless one accepts their political and economic theory, one is not likely to agree with their views concerning nature and knowledge, though it is only with the latter that I am concerned in these pages.

Engels and Lenin were firm materialists - that is to say, they believed that matter existed before mind, and that our minds reflect nature, and reflect it truly up to a point. But they absolutely rejected the current scientific theories of their day as complete or even satisfactory accounts of nature.

"The sole property of matter", wrote Lenin, "with whose recognition materialism is vitally connected, is the property of being objective reality, of existing outside of our cognition ... The recognition of immutable elements, the immutable substance of things, is not materialism, but metaphysical, anti-dialectical materialism...It is of course totally absurd that materialism should ... adhere to a mechanistic world picture of matter and not an electro-magnetic or some immeasurably more complicated one."

Writing of the physics of his own day, he said:

"Dialectical materialism insists on the temporary, relative, approximate character of all these milestones on the road of knowledge of nature."

Nature is in a state of perpetual flux - in fact, it consists of processes, not things. Even an electron is inexhaustible - that is to say, we can never give a complete description of it. We professors are always trying to give such a complete description, so that we can deduce all natural happenings from a few general principles. These attempts are successful up to a point, but we always find that nature is richer than we had thought. And the newly discovered properties of things appear to us as contradictions. Thus at the present moment both light and matter are found to have two sets of properties - one set resembling those of particles, and another set resembling those of waves. According to Engels and Lenin, things really embody a union of opposites, whose struggle makes them unstable and results in their development into something else. When we find "internal contradictions" in our conceptions about things our minds are mirroring nature.

But these internal contradictions do not mean that nature is irrational. They mean that it is unstable. Our brains are finite. Nature is probably infinite, certainly too large for us to take in. So our account of any material phenomenon is a simplification. We naturally think of things as neatly rounded off, and therefore tend to exaggerate their stability. However, the more we study nature, the more we find that what is apparently stable turns out to be the battlefield of opposing tendencies. The continents are the field of a struggle between erosion, which tends to flatten them, and folding and vulcanizing, which build mountains. For this reason they have a history. Animals and plants are never completely adapted to their environment, as Paley thought, and as they presumably would have been had they been made by an all-wise and all-powerful creator. On the contrary, they evolve just because they are imperfect. The same principle holds for human societies.

One of the materialist's greatest difficulties used to be perception. If the world consists of self-contained objects isolated from one another in space, how can any sort of image of it be formed in our brains! There is no hollow space in our heads where a puppet representation of the external world could be set up. Sound is the only feature of the external world about whose representation in our brain we know much. If we place an electrode on the auditory part of a cat's cerebral cortex and another somewhere else on its body, then in favourable circumstances if we amplify the current between them and pass it through a loudspeaker we actually hear sounds which the cat is hearing, or would hear if it were fully conscious. The same experiment is quite possible with a conscious human brain, though I don't think it has yet been done.

This means that the ear and the auditory nerve serve to set up electrical disturbances in air which we perceive as sound. In this case, then, there is an actual imaging of the external reality. But how can anything of this kind take place with a solid object seen or felt! The physical discoveries of the last decade have shown that ordinary material objects, from electrons upwards, can be regarded as periodic disturbances. Certainly the rhythm is very much faster than that of sound, and could not possibly be copied in the brain. But some kind of rhythmical changes in the brain, though very much slower than those which they mirror, would be copies of at least one aspect of matter.

The physicists tell us that the frequency of the vibrations associated with a particle are proportional to its mass, and the physiologists, in studying the impulses in a nerve fibre from an end organ responsible for our touch or pressure sense, find that the frequency of the impulses increases with the stimulus, though not in exact proportion. We do not yet know in any detail what happens in the brain when we feel pressure, but it is likely that a similar law holds good.

We are only on the very fringe of the necessary investigations, but it is becoming daily more plausible that our minds are physical realities acted on by the rest of the world and reacting on it. Our minds are processes which occur in our brains. Until recently it was quite impossible to see how the processes going on in thousands of millions of cells could possibly form a unity such as we find in our consciousness. We are now, however, discovering both in atoms and molecules properties of a system as a whole which cannot be located at any particular place in it. There is nothing in any way mystical about these properties. They can be very precisely measured and calculated. They are expressions of the fact that the various constituents of nature are much less isolated than was at one time thought.

The difficulties about truth are complicated by the fact that we use the word for at least three very different relations. We may mean that a perception or idea in a mind is true if it corresponds to an external reality. If the relation between the two is one of likeness it can never be complete, but it may be true enough for a particular purpose. We may mean that a physical copy or image is like its original. Or we may mean that a statement is true. This statement may be in words or other symbols, and logic is largely concerned with the truth of statements. Their truth or otherwise depends on the meaning of the symbols. This is a social matter. A statement is true only as long as someone understands it. After that it is meaningless. "Iron is heavier than water" will be true only as long as someone understands English, even if he is only an antiquarian. After that it will be gibberish like "Pung twet maboroohoo", which for all I know meant something to the men who built Stonehenge, but is neither true nor untrue today.

Of course the philosophers say that a symbolic statement stands for a mental reality called a judgment, which is independent of language. I think this is extremely doubtful. On the contrary, it seems much more likely that language began with words or phrases whose English equivalents would be "Come here", "Wolf!", "Heave-he", "Darling", and so on, which are not statements, and neither true nor false. And one can certainly think without making statements or judgments, as when one remembers the plan of a town and picks out the quickest route, or imagines what an acquaintance will do in given circumstances.

The great advantage of the theory that judgments are anything but sentences repeated in our heads is that it gives philosophers a chance to theorize about thought without investigating the physiology of the brain. This enables them to tell us a lot about truth, but very little about how we get to know it or how we act on it. If we take the view that a statement is true in so far as it calls up mental images which correspond to reality, and useful in so far as it incites actions appropriate to the real situation, we have got away from metaphysics, and are up against problems concerning the action of the brain, the history of language, and how we learn language as children, which cannot be solved by pure thought, but only by studying the real world.

For such reasons as these I find materialism intellectually satisfactory. I also think it is useful because it leads to actions of which I approve. Mankind is up against a very difficult situation. We have dealt with a great mass of problems in the past by scientific thinking - that is to say, materialistic thinking. We try to solve our political problems by appeal to eternal values. But if we start thinking materialistically about these "eternal values" we find that they are social phenomena which have come into being in the last few thousand years, because men gave up hunting and took to husbandry, agriculture, and handicraft. So society became a great deal more complicated, and "eternal values" are part of the apparatus by which it has been kept going. In particular they are very useful to those who are in comfortable situations at present, and would like the present state of things, with a few minor modifications, to be eternal.

Materialistic thinking in the past has been revolutionary in its effects. It has built up natural science and undermined religion. The same process is going on today. We have to realize that our current ideas about society are mostly very like our ancestors' ideas about the universe four hundred years ago - irrational traditions which stifle progress in the interests of a small minority. These ideas are being transformed by materialistic thinking about history as our ancestors' ideas were transformed by materialistic thinking about nature. The consequence will no doubt be revolutionary, as it was in the past. This would perhaps be deplorable if our society were working well. But it is working very badly. So we are probably going to have an uncomfortable time in the immediate future, whatever happens. And as I want a rational society to come out of our present troubles I am not only a materialist myself, but I do what I can to make other people materialists.

What is Life?

London: Alcuin Press, 1949

I am not going to answer this question. In fact, I doubt if it will ever be possible to give a full answer, because we know what it feels like to be alive, just as we know what redness, or pain, or effort are. So we cannot describe them in terms of anything else. But it is not a foolish question to ask, because we often want to know whether a man is alive or not, and when we are dealing with the microscopic agents of disease, it is clear enough that bacteria are alive, but far from clear whether viruses, such as those which cause measles and smallpox, are so.

So we have to describe life in terms of something else, even if the description is quite incomplete. We might try some such expression as "the influence of spirit on mater." But this would be of little use for several reasons. For one thing, even if you are sure that man, and even dogs, have spirits, it needs a lot of faith to find a spirit in an oyster or a potato. For another thing, such a definition would certainly cover great works of art, or books which clearly show their author's mind, and go on influencing readers long after he is dead. Similarly, it is no good trying to define life in terms of a life force. George Bernard Shaw and C.E.M. Joad think there is a life force in living things. But if this has any meaning, which I doubt, you can only detect the life force in an animal or plant by its effects on matter. So we should have to define life in terms of matter. In ordinary life we recognise living things partly by their shape and texture. But these do not change for some hours after death. In the case of mammals and birds we are sure they are dead if they are cold.

This test would not work on a frog or a snail. We take it that they are dead if they will not move when touched. But in the case of a plant the only obvious test is whether it will grow, and this may take months to find out. All these tests agree in using some kind of motion or change as the criterion of life, for heat is only irregular motion of atoms. They also agree in being physical rather than chemical tests. There is no doubt, I think, that we can learn more about life from a chemical than from a physical approach. This does not mean that life has been fully explained in terms of chemistry. It does mean that it is a pattern of chemical rather than physical events.

What is common to all life is the chemical events. And these are extraordinarily similar in very different organisms. We may say that life is essentially a pattern of chemical happenings, and that in addition there is a building of a characteristic shape in almost all living things, characteristic motion in most animals, and feeling and purpose in some of them. The chemical make-up of different living things is very different. A tree consists largely of wood, which is not very like the constituents of a man,though rather like a stuff called glycogen which is part of most, if not all, of our organs. But the chemical changes which go on in the leaves, bark, and roots of a tree, particularly the roots, are surprisingly like those which go on in human beings. The roots need oxygen just as a man does, and you can see whether a root is alive, just as you can see whether a dog is alive, by measuring the amount of oxygen which it consumes per minute. And the oxygen is used in the same kinds of chemical processes, which may roughly be described as controlled burning of foodstuffs at a low temperature. Under ordinary circumstances oxygen does not combine with sugarunless both are heated. It does so in almost all living things through the agency of what are called enzymes. Most of the oxygen that we use has to first unite with an enzyme consisting mainly of protein, but containing a little iron. Warburg discovered this in yeast in 1924. In 1926 I did some rather rough experiments which showed the same, or very nearly the same, enzyme in green plants, moths, and rats. Since then it has been found in a great variety of living things.

Just the same is true for other processes. A potato makes sugar into starch and your liver makes it into glycogen by substantially the same process. Most of the steps by which sugar is broken down in alcoholic fermentation and muscular contraction are the same. And so on. The end results of these processes are of course very different. A factory may switch over from making bren guns to making sewing machines or bicicyles without very great changes. Similarly the chemical processes by which an insect makes its skin and a snail its slime are very similar, though the products differ greatly.

In fact, all life is characterised by a fundamentally similar set of chemical processes arranged in very different patterns. Thus, animals use up foodstuffs, while most plants make them. But in both plants and animals the building up and the breaking down are both going on all the time. The balance is different.

Engels said that life was the mode of existence of proteins (the word which he used is often translated as "albuminous substances"). This is true in so far as all enzymes seem to be proteins. And it is true in so far as the fundamental similarity of all living things is a chemical one. But enzymes and other proteins can be purified and will carry on their characteristic activities in glass bottles. And no biochemist would say they were alive.

In the same way Shakespeare's plays consist of words, whereas words are a very small part of Eisenstein's films. It is important to know this, as it is important to know that life consists of chemical processes.

This pattern has special properties. It begets a similar pattern, as a flame does, but it regulates itself as a flame does niot except to a slight extent. And, of course, it has many other peculiarities. So when we have said that life is a pattern of chemical processes, we have said something true and important.

But to suppose that one can describe life fully on these lines is to attempt to reduce it to mechanism, which I believe to be impossible. On the other hand, to say that life does not consist of chemical processes is to my mind as futile and untrue as to say that poetry does not consist of words.

The Laws of Nature

Published in "Rationalist Annual", 1941.

The phrase "A law Of Nature" is probably rarer in modern scientific writing than was the case some generations ago. This is partly due to a very natural objection to the use of the word "law" in two different senses. Human societies have laws. In primitive societies there is no distinction between law and custom. Some things are done, others are not. This is regarded as part of the nature of things, and generally as an unalterable fact. If customs change, the change is too slow to be observed. Later on kings and prophets could promulgate new laws, but there was no way of revoking old ones. Thus the unfortunate Jews, if orthodox, stagger under a burden of law which was increased over thousands of years by ingenious rabbis. The Greek democracies made the great and revolutionary discovery that a community could consciously make new laws and repeal old ones. So for us a human law is something which is valid only over a certain number of people for a certain period of time.

Some people also believe in Divine laws which hold for all men everywhere. The curious can consult a report, Kindred and Affinity as Impediments to Marriage (SPCK), by Anglican bishops and others who have tried to solve the fascinating problem of where human law ends and Divine law begins as regards marriage with relatives. God forbids you to marry your sister, it appears, but it is not so sure whether it is God or man who says you may not marry your niece. So many gods have issued so many different laws in the past that a study of history makes the theory of Divine law a little ridiculous. Just the same applies to the Stoic conception of a natural law incumbent on all men as men. Even if such laws existed they would not be eternal, for man has evolved and will evolve. Actually they turn out merely to hold for a particular stage of social and economic development.

Laws of Nature, however, are not commands but statements of face. The use of the same word is unfortunate. It would be better to speak of uniformities of Nature. This would do away with the elementary fallacy that a law implies a law-giver. Incidentally, it might just as well imply a parliament or soviet of atoms. But the difference between the two uses of the word is fundamental. If a piece of matter does not obey a law of Nature it is not punished. On the contrary, we say that the law has been incorrectly stated. It is quite probable that every law of Nature so far stated has been stated incorrectly. Certainly many of them have. Nevertheless, these inaccurately stated laws are of immense practical and theoretical value.

They fall into two classes - qualitative laws such as "All animals with feathers have beaks", and quantitative laws such as "Mercury has 13596 times the density of water" (at 0 C and 1 atmosphere's pressure). The first of these is a very good guide. But it was probably not true in the past. For many birds which were certainly feathered had teeth and may not have had beaks. And it is quite possibly not true today. There are about a hundred thousand million birds on our planet, and it may well be that two or three of them are freaks which have not developed a beak, but have lived long enough to grow feathers. It was thought to be a law of Nature that female mammals (defined as warm-blooded vertebrates with hair) had mammary glands, until Professor Crew of Edinburgh found that many congenitally hairless female mice lacked these organs, though they could bear young which other females could then foster.

And quantitative laws generally turn out to be inexact. Thus water is nothing definite. It is a mixture of at least six different substances. For in the molecule H₂O one or both of the hydrogen atoms may be either light or heavy, and so may the oxygen atom. Similarly, mercury consists of several different types of atom. Thus the ratio of the densities of mercury and water is not fixed, though in the case of ordinary samples the variation is too small to be detected. But it can be detected if the water happens to have been taken from an accumulator which has been used for some time.

We have, I believe, gained a somewhat deeper knowledge of the meaning of natural laws from the work of two living English physicists - Jeffreys and Milne. In his Theory of Probability (Oxford, 1939) Jeffreys has something new to say about induction. Two contradictory theories are in vogue as to the laws of Nature. The older view is that they are absolute, though of course they may have been inaccurately formulated. The extreme positivistic view, enunciated by Vaihinger, is that we can only say that phenomena occur as if certain laws held. There is no sense in making any definite statements, though it is convenient to do so.

Now Jeffreys points out that, if a number of observations have been found to conform to a law, it is highly probable that the next one will do so whether the law is true or not. In Jeffrey's words: "A well-verified hypothesis will probably continue to lead to correct inferences even if it is wrong." This can be proved in detail if it is stated with sufficient exactitude, on the basis of some highly plausible assumptions. Thus we can use the "as if" principle without denying the existence of natural laws. What is more remarkable, laws which ultimately turn out to be inexact are often far more exact than the data on which they are based. Thus Jeffreys remarks, speaking of gravitation, that "when Einstein's modification was adopted the agreement of observation with Newton's law was three hundred times as good as Newton ever knew".

Positivists and idealists have made great play with the fact that many laws of Nature, as formulated by scientists, have turned out to be inexact, and all may do so. But that is absolutely no reason for saying that there are no regularities in Nature to which our statements of natural law correspond. One might as well say that because no maps of England give its shape exactly it has no shape.

What is remarkable about the laws of Nature is the accuracy of simple approximations. One might see a hundred thousand men before finding an exception to the rule that all men have two ears, and the same is true for many of the laws of physics. In some cases we can see why. The universe is organized in aggregates with, in many cases, pretty wide gaps between them. Boyle's law that the density of a gas is proportional to its pressure, and Charles's law that the volume is proportional to the temperature, would be exact if gas molecules were points which had no volume and did not attract one another. These laws are very nearly true for gases at ordinary temperatures and pressures, because the molecules occupy only a small part of the space containing the gas, and are close enough to attract one another only during a very small part of any interval of time. Similarly, most of the stars are far enough apart to be treated as points without much error when we are considering their movements.

And most men manage to protect themselves from injury so far as is needed to keep both ears. Whereas trees cannot protect themselves from the loss of branches. It is very rare to see a completely unmutilated, and therefore completely regular, tree. Mendel's laws, according to which two types occur in a ratio of 1:1 in some cases and 3:1 in others, are theoretically true if the processes of division of cell nuclei are quite regular, and if neither type is unfit so as to die off before counts are made. The first condition never holds, and the second probably never does. But the exceptions to the first condition are very rare. In one particular case a critical division goes wrong about once in ten thousand times. The effect of this on a 1:1 ratio or 3:1 ratio could be detected only by counting several hundred million plants or animals. Differences in relative fitness are more important. But even so the Mendelian ratios are sometimes fulfilled with extreme accuracy, and are generally a good rough guide.

Jeffreys points out that in such cases it is often much better to stick to the theoretical law rather than the observed data. For example, if you are breeding silver foxes and a new colour variety occurs which, if crossed to the normal, gives 13 normal and 10 of the new colour, you are much more likely to get a ratio of about 1:1 than 13:10 if you go on with such matings, even though if you breed many thousands the 1:1 ratio will not hold exactly. The mathematical theory which Jeffreys has developed concerning such cases is particularly beautiful, but can hardly be summarized here.

Milne's theories are extremely revolutionary. He starts off with very simple postulates. He assumes some geometrical axioms - for example, that space has three dimensions - but does not assume Euclidean geometry. He also assumes what he calls the principle of cosmological relativity - namely, that observers anywhere in the universe would see much the same things. There is no favoured point or centre, no limit beyond which there is no more matter, and no direction in which matter progressively thins out. This is an assumption, but it is only the natural extension of Copernicus's theory that the earth is not the centre of the universe butjust one star among others.

He then imagines observers on different stars communicating by light signals. This is, of course, unrealistic. But I have little doubt that, if his cosmological views prove valuable, later workers will be able to replace it by a more realistic hypothesis. Given this possibility of signalling, and Jocks, he shows how the observers can graduate their clocks and establish a geometry. There is nothing very surprising in this. What is remarkable is that Milne claims that he can deduce some physical laws as necessary consequences of his basic assumptions. In particular, he deduces a law of gravitation which reduces to Newton's at "small" distances measurable in units less than light-years.

This does not seem impossible. The law that the angle in a semicircle is a right angle was first observed as being at least very nearly true. Then twenty-five centuries ago Thales opened a new era in human thought by proving that it must be true. Milne may be a new Thales. Of course, later mathematicians showed that Thales, and Euclid too, had made a number of concealed assumptions. The proof was not as simple as they thought. And even if Milne's theories meet with no stronger criticism, they will doubtless meet with this one.

Milne claims that some, and perhaps all, physical laws are inevitably and rationally linked. He accuses those who say that laws might be otherwise of using "magical", not rational, thinking. Dirac goes even further, and suggests that there is nothing chancy about the distribution of the matter in the universe, and that an all-wise mathematician could deduce this too from a few postulates. I must say I find this much harder to swallow. Laplace's theory, that given a full knowledge of the universe at one time one could deduce its state at all times past and future, was difficult enough to believe. This is worse. But in so far as any elements in these theories are accepted, this will be a signal triumph for Rationalism as against theories which recognize an irrational element in the universe.

However, if Milne simplifies natural laws with one hand, he complicates them with the other. Lengths may be defined in two ways. They may be referred to a material object, such as the standard metre, or to a wave-length of light which has the merit that it can be reproduced anywhere. If all the standard metres were lost, they could be reproduced with an accuracy of about one in thirty million by reference to known wave-lengths such as that of the red cadmium line derived from spectroscopic observations. One result of Milne's calculations is that the length of the metre, measured in standard wave-lengths, is increasing by about one part in twenty million per year. If you like, you may say that the universe, including the standard metre, is expanding. But it is simpler for most purposes to say that atoms are vibrating quicker. It makes not the slightest difference to any observable phenomenon which of these statements you choose. in fact, on this theory, and indeed on several others which have been worked out in less detail, many of the laws of Nature are changing. There is nothing arbitrary or haphazard about this change, but simply an increase in certain physical constants with the time.

This has important philosophical consequences. If true, it rules out any theories of a cyclical or recurrent universe. At a sufficiently early date the properties of matter were so different, and in particular chemical processes so sluggish, that life must have been impossible, or, to be accurate, material systems similar to any existing organisms could not have lived. Thus we can see why, even if the universe had no beginning, life has not got very far yet. And in the far future life will also be impossible for beings constituted like ourselves, though it may be that our descendants could keep up with changes in the laws of Nature by natural or artificial evolution.

Once again, I am sure that Milne's theories, even if they are partially correct, will turn out to be too simple for the immense complexity of the real world. But they give us at least an inkling of how posterity will think of natural laws. So far from being laid down by the arbitrary word of a creator, they may prove to be a system as intimately and rationally knit together as the propositions of geometry, and yet changing and evolving with time like the forms of plants and animals.