immediate cause of old age, a means might be discovered of counteracting for a time the effects of these bacteria. But the discovery of the immediate cause of old age would not disprove the fact that individuals have evolved, through the process of selection outlined above, having a particular power of resistance to these bacteria.

In conclusion it may be said that selection favors a certain minimum life period for those who reach maturity but that this minimum is below the actual attainment of senility. The life cycle of man, as well as of lower animals, seems to be associated with the rate of reproduction, the object of this relation being to ensure survival. From this point of view the average life of individuals reaching the reproductive age seems to be sufficiently long. If it is ever prolonged still farther, as many think it should be, the gain must come about through some other advantage than the mere survival of the race. And there are advantages of an individual nature. For example, selection may so favor individuals possessing endurance or special resistance to disease, that the life periods of a larger and larger number will be prolonged. Yet even then families possessing the requisite fertility without exceptional vitality, would survive, thus keeping down the average length of life. It is hard to see how the duration of life of a people as a whole can be prolonged unless in it inheres a survival value for the species. More perfect adaptation to the environment, however, will result in an increase in the average length of life and possibly also in a slight prolongation of the life period.

Probable Effects of an Increase in the Life Period. An increase in the life period would bring both advantages and disadvantages, some of which might be of sufficient importance to be included among the factors determining length of life in the long run through selection. On the side of social profit it may be said that as population increases with greater adaptation, the more strenuous competition resulting will require greater specialization and a longer period of preparation; and the prolonged life will in a sense offset the longer time spent in preparation, giving individuals an equal if not a greater period of activity. The longer the working life as compared with the period of preparation the greater the economy. Therefore a longer active life would be advantageous as specialization progresses.

One of the dangers of the longer life period is from undue conservatism. Men are naturally more conservative after middle life than before it; and if the working time were lengthened it would mean that individuals would retain their positions longer and the average age of persons in active life would be greater. Extreme conservatism, however, is not necessarily a characteristic of maturer years, though increasing conservation is. Conservatism means stability as over against change or progress. Now change is desirable so long as there is an immediate necessity for adapting the environment to needs; but it involves the use of a greater amount of energy in readjustments to new conditions. The time comes eventually when alterations in the physical environment are less urgent, the chief changes occurring in the social environment. It then becomes important to conserve the progress already attained and a larger proportion of those forces making for stability are desirable. Furthermore, as adaptation becomes perfected, society finds the experience and judgment which comes with maturity much more valuable than the mere enthusiasm and energy of youth. There is a great difference, however, between conservatives and reactionaries. If society should come to be controlled by reactionaries it would be a matter of regret, because such control would result in a stationary condition of society.

Another possible disadvantage of the longer life period is that men become less energetic as old age approaches, and consequently some enterprises would suffer by being in the hands of individuals no longer in the period of greatest activity. On the other hand, it may be argued that the total social energy would be greater, for more people would be engaged in active work and the added competition would stimulate increased effort. The problem would become one of the proper distribution of work between those of greater energy and those of greater experience.

On the whole it would seem that a gradual prolongation of the life period would be advantageous as adaptation is perfected, although extending the length of life without increasing adaptation might result in loss rather than in gain to society. However, the more practical problem at the present time is that of reducing the casual death rate, because comparatively few individuals as yet attain what may be considered the normal limit of the life period.

Analysis of the Accidental Death Rate. The causes of accidental deaths from the social point of view may be divided into three classes: first, constitutional defects, such as heart disease, apoplexy, or premature births; secondly, imperfect adaptation to the physical environment, organic and inorganic, including all fevers due to the effects of microbes, starvation, etc.; thirdly, imperfect adaptation to the social environment, including suicide, murder, alcoholism, and kindred causes. The number of deaths falling into each of these classes cannot be estimated accurately from the reports of causes of deaths. But it would appear that in times of peace a very small proportion, probably not more than one-twentieth, result from imperfect adaptation to the social environment, while without doubt the great majority, not less than two-thirds, result from imperfect adaptation to the physical environment, the remainder being traceable to constitutional defects. Not all constitutional defects are inherited; and deaths resulting from those which are inherited are not always selective, for organic weaknesses frequently appear in serious form only late in life after children have been born who have inherited the weakness. When constitutional weaknesses appear early in life then deaths from them are closely allied to those resulting from imperfect adaptation to the environment, for a constitutional weakness may lessen the resistance of an organism to disease germs and individuals may die of fevers which normally they should have been able to withstand. However, the essential difference between these two causes of death is clear. In cases of constitutional weakness the chief trouble lies wholly in the organism, and in cases of imperfect adaptation the cause of the trouble is usually divided between the individual and the environment. A defect consisting merely of low powers of resistance to a particular disease germ is not here counted as an organic defect, though it may be inherited.

The elimination of inherited organic defects will have to be brought about through the process of selection; but in perfecting adaptation to environment, selection, though a possible means, is, under present social conditions, the slowest and most costly method of accomplishing the result. Ordinarily the adaptation should be active through a change in the environment, whenever scientific knowledge is sufficient to permit it. In case of deaths arising from lack of adaptation to the social environment the trouble may seem, in the first instance at least, to lie with the individual; but the individual is the result of his environment as well as of heredity and the most effective reform requires social improvement as well as individual treatment.

Summary. To recapitulate, the causes of accidental deaths may be traced chiefly to imperfect adaptation to the physical environment, a condition made worse by the severity of competition in the industrial world. Deaths traceable to this cause will be reduced by the progress of science, by a greater appreciation of the value of human life, and by an improvement in the condition of the poor. Secondly, this excessive mortality may be attributed to the birth of offspring having constitutional defects. Deaths from this cause may be reduced by an improvement in sexual selection, by an increased knowledge of the laws of heredity, and by a feeling of greater responsibility towards the second generation. And finally, a few deaths are

a due to imperfect adaptation to the social environment, and effective reform here requires both social and individual treatment.

Relationship Between Births and Deaths. Although the birth rates and death rates have been discussed separately in the last two chapters they are not entirely independent phenomena. Examination of the rates for different countries shows that in a general way the two vary together; countries with a high birth rate usually have a high death rate also, and a low birth rate is ordinarily accompanied by a low death rate. In explaining this phenomenon it will be found that both the birth and death rates react on each other, each being cause as well as effect. The tendency of a high birth rate to produce a high death rate is generally recognized. It was included in the Mal

thusian teaching and has perhaps been over-emphasized. A high rate of reproduction causes over-crowding among the poorer classes, which conduces to less sanitary conditions and leads to the neglect of children on the part of parents. The result is a high rate of mortality, especially of infants.

On the other hand, M. March says: “The death rate governs the birth rate far more than the birth rate governs the death rate.” A high death rate permits the continuance of a high birth rate. If the death rate should decline it would finally react to decrease the birth rate at least among that part of the population having the higher standards. The increased population resulting from the lower death rate makes the struggle for life more acute and lowers the birth rate among those who are influenced by “social capillarity.” On the other hand a high death rate lessens the severity of competition and permits the birth rate to continue undiminished. The fact is that among people with low standards it is the birth rate which manifestly affects the death rate, while among people with high standards the death rate is the more active agent and it reacts upon the birth rate.

This automatic regulation of births and deaths is a part of the process of adaptation to the environment. To explain the process more fully we may revert to the three factors discussed in the previous chapter; the environment, the standard of living, and the rate of multiplication. The provisional statement that the birth and death rates vary together should now receive some qualification. The birth and death rates are both high or low in countries in which the environment is comparatively stable. With unchanging environmental conditions, if the standards of living are low, or in other words if the people are unprogressive, the birth and death rates will both be high. This is the condition in such countries as Spain, Austria, Bohemia, and Russia. If the standard of living is high, the birth and death rates will both be low. This is the case in most of the northern European countries. The birth and death rates may diverge more widely in countries in which wealth is increasing. In such a case the progress of science and sanitation may lower the death rate without having much effect on the birth rate, because the in