CAN MAN CONTROL HIS NUMBERS? [Darwin essay] : LUSENET : Running on Empty - The Coming Petroleum Exhaustion Dieoff : One Thread


Sir Charles Galton Darwin

When I was honoured by the invitation to make a contribution to this symposium, I was embarrassed by the fact that all the other contributors were professional experts in the various subjects associated with evolutionary theory, whereas my own claims could at best be classed as those of an amateur. I have therefore chosen a subject where perhaps I can get on closer terms with the rest, because forecasting on incomplete data is related to statistical theory, a subject of some of my earlier studies.

Most of the contributions to the symposium are concerned with the way our knowledge has expanded during the past century, and it seemed it would not be uninteresting to attempt an estimate of the probable state of the world at the times when there might be celebrations of the second and later centenaries of 1859. Interesting contributions to the subject of man's future have been given by Huxley and Muller, and I certainly cannot aspire to making criticisms of their work. My own aim has been to deal with a far shorter range of time than they do, though I shall permit myself a few comments on the remoter future, too.


It can be taken as established by the demographers that our present world population of more than two and a half billion will almost surely have become at least five billion by the end of the twentieth century. No famines or pestilences on any reasonably probable scale can affect this, and war of the old type would also be quite unimportant. Even an atomic war would hardly be likely to make a great difference by its direct effects, but it must be recognised that there would very probably be a breakdown of world economics, with consequent killing of many more---perhaps even half the world---by famine. However, I do not propose to pay consideration to atomic wars because of the present great uncertainties about them.

According to expert agricultural opinion, it should be possible to feed these five billion. It may call for the enforcement of better farming methods in many places, and also for great outlay on irrigation schemes. Also, it may require what may be called the charitable transfer of food from parts of the world where there has been overproduction to other parts suffering from shortage. According to the experts, it should be possible in this way to raise food production to double the present quantities, and so to feed the doubled population. this of course, is not as happy a result as might appear at first sight, because we have to remember that, even now, half the world is undernourished.

The world, then, seems to be capable of dealing with the problems of the next fifty years without taking any very radically new kind of action, but what will happen then? Why should not the population tend to double again in the following fifty years up to ten billion, and this would certainly strain the resources of the finite area of our Earth. We have got onto the Malthusian spiral of geometrical increase, and we must ask whether anything can be done to prevent our relapse into the hard conditions of most ancient periods of history when the escape from the spiral was through recurrent famine, pestilence, and massacre.

It will be seen that quite a new feature has now entered into our outlook on human life. In the old days, population used to fluctuate about roughly constant numbers, being held there by natural selection. In judging whether some past epoch had been a good or a bad one, it was quite reasonable to make the estimate by merely counting heads; a good epoch would be one when numbers were increasing, a bad when they were diminishing. But now, we are free from the ruthless action of natural selection, and we are faced with the prospect that increase will be a bad thing, because it may lead to a disastrous lowering of world conditions. We are being forced to make a revolutionary change in our standards of value, and in view of the conservatism of the human mind, there may well be difficulties in persuading a majority of human beings of the necessity of this revolution.


In his contribution, Huxley has propounded the view that the way of the world has been radically changed through the emergence of man's mind. He claims that there can be no further really important biological evolution of the old kind among animals. In particular, there is no possibility of any animal emerging as superior to ourselves, for the reason that we should see the threat and exterminate the animals before things had gone too far. Indeed it does seem likely that the most extreme evolution that will occur among animals in the future will not be among wild animals but among domesticated ones, where man's control, from generation to generation, in changing their forms, can operate much more quickly and continuously than ever would natural selection.

Huxley then goes on to claim, I think rightly, that for the future a new kind of evolution will emerge which he calls psycho-social. Man will evolve less through his genetic nature, than because he has the capacity of sharing his knowledge with his fellows so that the processes of human life are controlled in a manner radically different from anything that has gone before. The human race has indeed discovered how to make certain types of acquired character heritable through the processes of education and mutual instruction, and this is a tremendous revolution.

In his interesting contribution, Muller follows up the same subject, and examines its genetic consequences in some detail. He emphasizes the formidable difficulties with which we shall be faced on account of the recurring development of deleterious mutations. Indeed, if his subject is thought of as a proposition in general and not merely in human biology, it is hardly an exaggeration to say that the Mendelian laws of heredity absolutely require a very severe form of natural selection for their successful operation. Only so will the perpetually recurring deleterious mutations be eliminated, so that opportunity will be given for the much rarer beneficent ones to come into play. He takes it for granted that we need to have a world from which ruthless natural selection is eliminated, and he shows how, by close attention to genetic principles---many of them already very nearly within our reach---we might hope to keep within bounds the evil effects of mutation.

We may all agree with these view of Huxley and Muller, subject to the conditions that man really does succeed in freeing himself permanently from natural selection in the old sense of the term. Man can now aspire to the complete mastery of nature, but subject to the one condition that he can master himself. I shall later discuss in more detail the prospects for this mastery, but here I will only point out the extreme urgency of the matter, for unless the problems are all solved within half a dozen generations, population pressure is likely to be so great, that there will be a return to the old conditions of the struggle for life. The evolution may still be mainly of the psycho-social type, but it will have none of the pleasing rather utopian qualities which we might have hoped for.


It is appropriate to examine more closely the new type of heredity that has emerged. I use the clichi of this title in the sense that Nature is meant to cover the purely genetic qualities of our race, while Nurture applies to the qualities we derive from education and social contact. The term "culture" is sometimes used for this purpose, but it tends to have an emotional significance which I want to avoid.

To judge from the study of fossilized brain-cases there is no clear indication that mankind has grown in intelligence since the evolution of Homo sapiens. His Nature has made little further contribution to his status in the world, and yet this has been fantastically altered as judged by the standard of his numbers. Leaving aside such things as the invention of tools and of fire (which preceded the emergence of Homo sapiens) his first great increase derived from the invention of agriculture ten thousand years ago, and this gradually increased his numbers by a factor of perhaps five or ten. Five thousand years ago he invented civilization, which again gave an increase on a similar scale. But, these two multiplications have been entirely put in the shade by the increases of the past two centuries due to the Scientific Revolution, for during this short space he has multiplied his numbers a further five times, and these increases are still continuing at an even greater rate. Considered merely by the standard of numbers, Nurture has proved itself immensely more important than Nature.

In spite of these quite overwhelming results from Nurture, I must confess that I believe that in the long run Nature is more important. Thus, Nurture has contributed these three great inventions, but when we consider the lesser details of its effects they show an instability that is disappointing. Each of us undoubtedly owes most of our conduct and of our creeds to education, but in many important matters we tend to hold quite different opinions from those of even the preceding generation, and this hardly seems to accord with any obvious law of heredity. In the present changing conditions of the world, with the rapidly increasing fields of knowledge, the departure from the views of our fathers may not be surprising, but the weakness of Nurture heredity is not limited to this phase of our experience, as may be illustrated by an example taken from past history. Thee can be no doubt that one of the most important things inculcated by Nurture has been religion, and therefore one might hope it would be one of the most durable. Now though, it may be argued that the Christian doctrines have endured for nineteen centuries, there can be no doubt that the enthusiasm associated with those doctrines have changed every few centuries. These enthusiasms were the things for which men were ready to die, and there seems no uniform thread running through them at all. Thus, the important things for the Reformation were quite different from those for the Crusades, and these again were quite different from the curious doctrinal heresy-hunting campaigns of five centuries before.

This example seems to suggest that the new kind of heredity working on Nurture has none of the permanence of the Mendelian type working on Nature. In spite of the immense importance that most people attach to religion, it seems that its enthusiasm only endure for less than say five centuries. The heredity of Nurture thus seems rather to resemble the cruder old idea that each generation will tend to revert half way back towards the normal, so that in say ten or fifteen generations its effects will have become negligible.

In studies of history, generalization is notoriously dangerous, because history never really repeats itself, but it would surely be interesting for historians to attempt to examine this intensely important subject in the hope that there might emerge something like principles of heredity in the evolution of opinion and conduct. But, if I am at all correct in the example I have taken, the conclusion is that there is little of permanence in Nurture heredity, always excepting the three great examples of agriculture, civilization and science which I have cited and the possibility that one day some genius may make a new invention of similar importance.

Anyone wanting to press a new good cause on his fellow is always in danger of thinking that, if only he could persuade the world, everything would become perfect, but this must not blind us to the fact that Homo sapiens, like any other animal species, is likely to maintain the general characteristics of his hereditary Nature nearly unchanged for something like a million years. Thus, a certain fraction of mankind---and not a very small one---tends to turn to crime, and it is to be doubted if the proportion varies very much. It may be true that in times of high prosperity there is less of what may be called the hungry man's crime, from the simple fact that no one is hungry. But, there is much crime that cannot be excused by this stimulus, and it is to be doubted if this other type has become any rarer. Are not bank-robberies and fraud and crimes of violence just as common as they ever were? Is it not likely that there will be criminals who continue to disgrace the brave new world we are all hoping for, and that they will not respond to the benevolent treatment planned for their conversion?

In certainly do not aspire to make any definite judgment in this matter of the general rivalry between Nature and Nurture, but I have been attempting to set forth the case that, contrary to the hopes of many people, man's Nature will continue to dominate the world.


When any species of higher animal succeeds in maintaining its numbers in the next generation, it does so mainly by the possession of three instincts: the instinct of self-preservation, the sexual instinct, and the parental instinct. As to the first of these I need not speak. In regard to the other two there is considerable variation in that some animals produce quite a large brood, of which few survive, while others may produce only three or four young in the course of their whole lives. Of course, any animal must on the average produce at least more than two offspring if its numbers are to be maintained.

Man is endowed with the same instincts, and I propose to continue calling them "instincts" even though the word may have acquired some more technical meaning in modern psychology. Indeed, in some respects he has these instincts more strongly than have most animals. Thus, most mammals and birds become sexually inclined during only part of the year, whereas man and the monkeys have no relaxation from the instinct all year round. As to the parental instinct, it has, of course a very different quality from the sexual in that it has to maintain its vigour so long as the young still need protection. With most animals this signifies a few months, but for man it means something like twenty years. Both sexual and parental instincts have been maintained by natural selection. Thus, anyone with a weak sexual instinct would be apt to beget few children, and again any parents who are not driven to care for their children by the affection which is the conscious working motive of the parental instinct, will lose a greater fraction of them. Since we have to believe that instincts are heritable, it is evident that these qualities will be possessed by a population to the degree that may be required in order to ensure the maintenance of its numbers.

Until a short time ago, these two instincts sufficed to maintain human populations, but the ingenuity of man has contrived to find and to exploit a gap in his equipment of instincts by the recent developments of birth-control. Thus, the sexual instinct can be fully satisfied without paying the price that used to be inevitable. Again, the parental instinct in most people seems to acquire its full force only after the birth of the child, and it appears that it can be more or less satisfied by lavishing all the parental affection on even a single child.

If I may be permitted so to put it, by the invention of contraception, the species Homo sapiens has discovered that he can become the new variety "Homo contracipiens," and many take advantage of this to produce a much reduced fraction of the next generation. We have found out how to cheat Nature. However, it would seem likely that in the very long run Nature cannot be cheated, and it is easy to see the revenge it might take. Some people do have a wish for children before they are conceived, though for most of them it has not the strong compulsion of the two instincts. There will be a tendency for such people to have rather more children than the rest, and these children will tend to inherit a similar wish and so again to have larger families than do others. In succeeding generations there will be some who inherit the wish to an enhanced extent, and these will contribute a still greater proportion of the population. Thus, the direct wish for children is likely to become stronger in more and more of the race and in the end it could attain the quality of an instinct as strong as the other two. It may well be that it would take hundreds of generations for the progenitive instinct to develop in this way, but if it should do so, Nature would have taken its revenge, and the variety Homo contracipiens would become extinct and would be replaced by the variety Homo progenetivus.

All this, of course, will happen only if the practice of birth-control becomes so prevalent that, through it, population numbers should actually tend to decrease.


In attempting a long term forecast, much consideration would have to be given to the possible evolutionary changes in man, but for the short term, say one of five or six generations, this difficulty does not arise, because there is no time for heredity to make any modifications in human nature. Two centuries hence, man can be taken to be practically identical in his nature with present-day man.

I have already alluded to the revolutionary change that must affect our mentality with the realization that increase in numbers is now likely to be an evil and not a good as it used to be in the past. In those days, the judgment depended on the antithesis between life and death, but with the development of birth-control the antithesis has fortunately been changed to one merely between life and non-life and this should be much more acceptable. There seems really no alternative to the development of birth-control as the only humane way of avoiding the threatened evils.

Birth-control is already a widely accepted practice, but most of the various methods are expensive, laborious, and unattractive. For there to be any prospect of its coming into world-wide use, something much better is an absolute requisite. This provokes strongly the question whether nearly enough study is being given to the matter, as contrasted with all the immense and costly research that is being done on other medico-biological problems, for example, on cancer. However, the work that is being done shows promise, and though success in the research has not yet been achieved, it looks to be not far off. We may hope that in the course of a few years there will be something, perhaps a "pill," which would be easy to use, easy to obtain, emotionally acceptable, and without undesirable collateral effects. If the attempt to achieve this should fail, we cannot hope that birth-control will make any really important contributions to the population problem, and we must fear that the increases will continue up to the point where natural selection will again play its ruthless part.

However, I shall assume that this is not so, and that soon we shall possess a really acceptable contraceptive pill. Even then, however, the problem will not have been solved, for large scale factories must be built to make the pill, and, more formidable still, there would be need of a vast educational campaign to instruct the whole world, which means dealing with everybody between the ages of 15 and at least 45 years, a total of perhaps a billion people all told. It would seem optimistic to expect that anything like this could be accomplished in under fifty years, and by that time the five billion of mankind will be already feeling the pressure of their numbers.


There will remain the formidable problem of administration, and the central difficulty in this is that the artificial control of numbers would have a natural instability. Thus, suppose that half the nations of the world succeeded in finding a way of limiting their numbers, while the other half refused to do so. In a few decades the limiters would be in a serious minority, and without going into the details of the matter, it is hard to believe that in the long run they could stand up against the vigour of the much more numerous non-limiters, trained as they would be in the hard battle for mere life. It is an open question whether the limiters would be conquered from above or from below, but a conquest from below by the boundless provision of cheap labour would be just as effective from the present point of view as the more usual type of conquest.

It would seem inevitable from these considerations that in the struggle for life a refusal to limit numbers gives a positive advantage. This raises the important point that even now the Roman Catholics forbid some of the proposed practices, and there are also many peoples who regard it as a proof of virility to produce a large number of children. We must hope that both these difficulties may be overcome, but here is still the danger that new creeds of the same kind might arise in connection with such an intimate and emotional matter as family-planning. Indeed, it is hardly too much to say that a firm belief that contraception is a sin would have a strong positive value in the struggle for life between different communities.

On the other hand, it must be recognized that, if anything can be done, now is the time for it, largely because of what I have called the gap in our instincts, through which we can satisfy our sexual wishes and our parental affection while making only an incomplete replacement of our numbers. In consequence of this gap, our emotions would not be much aroused by any limitations imposed on the numbers of our children. Thus, there are already examples where it has proved easy to control numbers in one direction or the other through legislation. A few years ago, France became anxious about its decreasing numbers, and by the provision of children's allowances in the taxation scheme the process was at once reversed. In the case of Japan, the danger was the opposite, and their terrifying increases have been stopped at least to a large extent by the legalisation of abortion, under which something like a million operations a year have been performed without apparently causing discontent.

An interesting feature about control by legislation is that it would be easy to give it a eugenic direction. At the present time, equalitarianism is so rampant in political thought that this would commend itself to few legislators, but there can be little doubt that if any country should carry out a eugenic policy for even a few generations, that country could dominate all its neighbours by the sheer increase in the ability of its people. Moreover, it would not be difficult to do this. There is no need to give thought to the particular qualities that are desired, because the aim would not be to produce highly exceptional people, but merely to raise the average of intelligence, relying on the operation of chance to produce the exceptions from among this raised average. Thus, people earning large salaries are likely to be rather abler than others, and much could be accomplished by merely arranging the system of taxation so that these people should be induced to have more children than the rest. Such a policy would be quite contrary to all political thinking in democratic countries at the present time, but there can be little doubt that the first country to embark on it, and to maintain it for a few generations, would reap a rich reward against its rivals.

There is an opposite aspect to this matter, and it draws attention to a condition to which we have already been exposed for a good many years. It has been the educated, intelligent and prudent people who have hitherto practised birth-control most, and these must therefore have been making a smaller contribution to the next generation than the contribution of the less prudent and the less intelligent. Any system of purely voluntary birth-control is all too likely to be adopted most frequently by such people, and so we are continually exposing ourselves to the danger of lowering the average of the intelligence of our nations. Even if no approval is given to a positive eugenic policy, it should be possible for legislation to counteract this negative tendency.


In the light of these views, I will attempt a forecast of the state of the world in the next century or two. I need hardly say that I realise that this is an over-ambitious task to undertake, and I would emphasize that all forecasting only deals with probabilities. I am giving what I regard as the more probable things that will happen, with no attempt at assigning any degree of certainty to them.

The central problem of the world, at any rate after the next fifty years, will be over-population. It will be mitigated to a considerable extent by increasing use of birth-control, but there will be no tome for this to develop to a degree that will remove the problem. As an example, it is hardly possible that it should reduce the five billion of fifty years hence to four billion.

Food production will be greatly increased to match these numbers, but it will remain true that half the world---and this, of course, means a greatly increased number---will still be undernourished. The principle will continue to hold that however much food is produced there will always be too many mouths asking for it.

Political habits of thought are very conservative, and in the course of two centuries they cannot be expected to change very much. At the present time the mutual jealousies between countries dominate political thought, and this jealousy will increase rather than diminish under the hardening conditions of life.

This has the consequence that a single world-government, so ardently hoped for by idealists, will not be achieved. However, it is worth glancing at one of the formidable difficulties it would have to face if it could be created. One of its main tasks, perhaps the most important of all, would be the control of population numbers in the various regions of the world. But, government requires not merely benevolent good will; it must also be able to enforce its rule by sanctions. What would the government do if it discovered that in some region the population was intentionally being increased beyond the numbers apportioned to it? It would seem that the ultimate sanction would have to be to kill off the excess. Is it likely that such an extreme step would ever be undertaken? But, if it were not, the consequence would be that the world-government would have failed in its main purpose.

In the light of this, each country will tend to adopt its own policy about the control of numbers. It will in fact be an easier task than it would be to do this now, because one of the effects of the harder conditions of life will be to diminish individual personal liberty in favour of the state, and already it has been seen that much can be done about controlling numbers by legislation.

In the far future, the instability inherent in the control of numbers may have a dominating effect, but during the short period contemplated it will not have time to exert this effect. Thus, some countries, probably those already most prosperous, will succeed in limiting their numbers, and so will be able to retain much of the present good life. Others will fail to do so, or perhaps either on principle or through the ambitions of power politics they will refuse to attempt it.

The world will thus be divided by the jealousy of the unprosperous directed against the prosperous. Under these conditions it is hard to believe that wars can be avoided, but it is to be hoped that they will be small wars of the old type, and not the major atomic wars which are so much in our minds at present. For a time at all events the superior equipment and culture of the countries with limited population should suffice to defend them against their more numerous opponents.

In the overpopulated countries, many of the characteristics of our civilization will survive, but they will be chiefly the superficialities because life will be too hard to permit the peoples to go deeper. On the other hand, in the countries that have succeeded in limiting their numbers progress will continue. New discoveries will be made which may tend to ease the life not only of these countries but of the whole world. Scientific knowledge will continue to advance. The torch of learning will still burn, and the great names of the past will still be honoured.

I am very fully conscious that the views I have expressed run entirely counter to many of the optimistic hopes of the present age. I myself see little prospect of escape from the return to hard conditions of life, and much of my motive in setting my views down is the hope that they may be contradicted by others who have a deeper knowledge than I can claim of the laws of Nature.

-- Scott (, May 10, 2000

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