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the death-rate, causing what has been described as a secondary fall therein. In the case of the small families of the well-to-do, another child being born would, however, very seldom cause a child already born to fail either to survive or to marry; and, consequently, amongst the well-paid strata the secondary fall in the juvenile deathrate is always smaller than, and can, therefore, never obliterate the primary fall in the birth-rate which caused it. Thus causes primarily tending to reduce the birthrate amongst the well-to-do always also tend to reduce the number of offspring surviving to manhood; and no assignable limit can be placed to the effects of this tendency. Turning now to the fall in the death-rate, a fall generally producing an opposite tendency to the fall in the birthrate, here, again, secondary effects have to be reckoned with. A primary fall in the death-rate, such as that due to improved sanitary conditions, for example, would generally produce a secondary fall in the birth-rate; but since keeping a child alive would not necessarily inhibit the birth of another child, this secondary fall in the birth-rate would not even in small families quite wipe out the average effects of the primary fall in the death-rate by which it was caused. Thus a primary fall in the juvenile death-rate, such as that which has certainly taken place in recent years, always tends to increase the size of the adult family. But, however low the death-rate might fall, this fall would afford no reason why the birthrate should not fall so low in any group as to reduce the average number of the fertile family to below two; when a decrease in the numbers of that group would set in. And this appears to be the stage at which our professional classes have now arrived.

If we turn to the ill-paid strata of society, it will be seen that all the foregoing arguments do not quite hold good. For the reasons given above, the causes tending to produce a fall in the birth-rate have been less operative where poverty exists, and, consequently, large families are now found amongst the lower social strata. But the larger is the average size of the families, the greater is the secondary fall in the death-rate as compared with the

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primary fall in the birth-rate which caused it; for we have seen that if families are large enough, a fall in the birth-rate may even cause an actual increase in the size of the adult and fertile family. A fall in the birth-rate in strata which are very prolific may, therefore, at first cause little or no decrease in their rate of multiplication. Then, again, where great recklessness prevails, a fall in the death-rate, due to modern improvements in sanitation, etc., would react but little on the birth-rate; because the survival of a child of thoughtless parents would produce no increase in their deliberate desire to limit the size of the family. Thus, for all these reasons, the larger the family the less effect would any advances in civilization have in reducing the rate of multiplication of the group in question.

The result of this long a priori argument is, therefore, to show that there are many theoretical considerations which are in harmony with, and none which run counter to the conclusions arrived at in the last chapter by a study of facts and figures; namely, that with advancing civilization the difference between the rates of multiplication of the ill-paid and well-paid strata of society have increased, are increasing, and in the absence of new factors will continue to increase.

SUMMARY AND CONCLUSIONS

The words natural infertility' have always been held in the foregoing discussion to include all human qualities, whether mental, instinctive or bodily, which tend to decrease the size of the family. The fall in the birth-rate in recent years has been due to the following causes :(i) The fall in the death-rate, which has caused secondary effects on the birth-rate. (ii) Increased celibacy or family limitation due to the increase in the numbers of those who are actuated by social ambition, this being the result of the removal of social barriers. (iii) The increase in time occupied in education and training, thus leading to later marriages and consequent diminished fertility. (iv) Such legislation as has lessened juvenile labour and reduced family incomes accordingly. And, underlying

all these causes, in so far as purposive action is concerned, has been (v) the increase in the knowledge of contraceptive methods. The fall in the birth-rate has been most rapid amongst the better-paid classes, and the consequent differences in the rate of multiplication of the different social classes is a comparatively new phenomenon. The many causes of this differential birth-rate may be summarized as follows:-(i) The absence of juvenile labour and the relatively high expenditure on education amongst the well-to-do classes. (ii) The earlier age at which the manual labourer marries as compared with the brain worker. (iii) The expensive habits of bachelors, which tend to delay marriage, especially amongst the wealthy. And (iv) those social advantages possessed by members of small families which aid them in mounting the social ladder. The increase in natural infertility and natural capacity amongst the better-paid classes due to these two last causes has been a slow process; but its effects certainly in some measure account for the comparative rapidity with which the upper social classes have adopted contraceptive methods. Influences affecting the death-rate are less easily dealt with; but, on the whole, a consideration of this side of the question merely serves to reinforce the conclusion arrived at on all other counts, namely, that with increasing civilization there is a tendency for the rate of multiplication of the least efficient classes steadily to increase as compared with that of the more efficient. The warning that all is not well with us is thus clear and emphatic; for it indicates that it will only be possible to maintain for long into the future our existing standards of culture and comfort if these causes of the decline in our racial qualities are vigorously combated.

CHAPTER XX

MATE SELECTION

We have seen that the greatest danger to our civilization in the future lies in the present rapid rate of multiplication of the inferior types, not merely of such as may be described as the definitely unfit. How is this danger to be averted? No doubt one proposal which will be made is that all men and women should be induced to exercise greater care in the selection of their mates in marriage; for at first sight it seems evident that any change in this direction must have beneficial effects on the race. That this is a true conclusion I do not doubt; though it has to be admitted that the more the matter is studied, the less important seem to be the future benefits which could be derived from more careful mate selection.

SEXUAL SELECTION AND EVOLUTION

Wonderful results have been produced, so at all events it has been claimed, by the action of sexual selection in regard to the evolution of all kinds of organisms which are endowed with the power of sense perception; and, if this be so, we ought to inquire in the first instance whether this same agency cannot be utilized in our efforts to improve the human race. In attacking this problem it may be as well to begin by giving a brief illustrative sketch of the way sexual selection either has or may have promoted evolutionary changes amongst the lower animals; even though the only object sought to be attained is to make some of the questions involved stand out more clearly.

The theory of sexual selection which is associated with the name of Charles Darwin has been subject to a good deal of hostile criticism in recent years; attacks which

appear to one who may be prejudiced to have been on the whole unsuccessful. We are still blankly ignorant concerning innumerable events which occurred in the remote past during the evolutionary history of existing organisms; and it would indeed be surprising if we could bring all we see around us into harmony with our evolutionary theories, however true they may be. We should accept provisionally the explanation which best fits in with known facts; for to wait for a theory which would explain everything would, to say the least, cause a most injurious delay. No doubt certain experiments seem to have indicated that nothing akin to the choice of a mate is exercised by certain birds and insects; but is it possible to imitate natural conditions so exactly as to remove all elements of doubt? The theory as originally propounded may no doubt need to be supplemented, as its author doubtless anticipated.

Sex may produce evolutionary results in two different ways. In the first place, there must often have been contests between two males in order to secure a mate, willing or unwilling as the case might be; and in this way qualities which make for success in combat may have been slowly evolved. Human nature probably still shows some relics of this evolutionary process; but as in civilized countries men now seldom actually fight for their brides, this aspect of the effect of sex on evolution will be entirely omitted. Here we shall only be looking to the effects produced by the qualities possessed by members of one sex in attracting to them the members of the other sex. Before passing on to consider this, the second method by means of which evolution has been affected by sex, it may be as well to say a few words as to the meanings of the words to be used.

The word 'selection' is apt to bring to the mind the idea of a desire to possess something, and we therefore expect successful selection to promote progress; whereas it may be either the better or the worse who are being chosen, and sexual selection may bring about either improvement or deterioration. Biology tells us nothing about ethics. Then, again, selection' seems to imply

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