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one which shows greater intelligence in resisting or avoiding their attacks. If the environment could be freed of deadly enemies, it is evident that this selective process could be avoided, and individuals susceptible to parasites would remain alive. So the social gain or loss from using the active or the passive form of adaptation in this case, depends largely upon the question of whether the attacks of micro-organisms tend to eliminate the physically and socially undesirable, or whether they merely eliminate those who lack a particular power of resistance. The fact seems to be that of those who adapt themselves to the inorganic environment, the weak and the strong alike are subject to attack from hostile organisms. Indeed those who are the stronger physically do not always show the greater resistance. Attempts have been made to prove that certain disease germs, such as the tubercle bacillus, are more likely to attack individuals of inferior physique, but the evidence presented has not been convincing; and on the other hand there are other fevers, such as typhoid for example, which seem to be hardest with the most robust. On the whole the eliminative process seems to apply chiefly to those who lack resistance to a particular organism, and resistance is not correlated with general physical superiority. Moreover from the point of view of the social qualities of a population this form of adaptation has no selective value whatsoever. It must be concluded therefore that heterogeneric selection is of little racial or social value. Whatever is gained by its elimination of the less desirable is more than offset by the destruction of the physically and socially superior. Wherever possible then the active form of adaptation to lower organisms should be preferred to the passive. Dangerous organisms should be eliminated from the environment and no adverse results need be feared. Where this is impossible, heterogeneric selection becomes inevitable, and even desirable, for adaptation must go on so long as a people chooses to remain in the same environment.

Losses from Heterogeneric Selection. The extent of the loss to society from the action of heterogeneric selection cannot be accurately given. Karl Pearson estimates that 80% of the deaths are selective, and the greater part of these would certainly be due to heterogeneric selection. In place of a quantitative

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exposition of its effects, illustrations of its ravages must suffice. For this purpose one of the worst enemies of man may be selected, a vegetable parasite known as the tubercle bacillus. Tuberculosis is the chief cause of deaths in the United States, though pneumonia has now become a close second. It is responsible for over one hundred thousand deaths in the registration area alone, or about 8.3% of the total number. Frederick L. Hoffman estimated the mortality from tuberculosis in five eastern states and ten cities as 23.2 per ten thousand, during the years 1886–1900, and this showed a decline from 30.7 for the period 1871–1885. Since 1900 a further gratifying reduction has been achieved. The census returns give the annual average for 1906–10 as 16.87 per ten thousand; and for 1915-18, as 14.57; while 1920 showed a still further reduction to 12.56. Hoffman points out that the decline has been more marked for females than for males, and that the rate for negroes has always been much higher than for whites. The extent of the ravages of this disease is shown in a more impressive form in a recent study by Dublin and Whitney ? from the records of the Metropolitan Life Insurance Company. It appears that white males suffer a loss of 3.5 years in their average life time because of tuberculosis, or 7.6% of their entire life expectancy. At the age of 20 it is 3.7 years. The loss for insured wage earners is somewhat higher than for the total population; but the average length of life of all individuals who survive to the age of 20 would be prolonged 2.4 years if tuberculosis were eliminated.

Interesting estimates of losses from the point of view of money costs have also been made. Hoffman says that in 1900 tuberculosis caused annually more than 150,000 deaths in the United States at the average age of 35 years, so that the total loss of life is represented by 4,800,000 years per annum. Estimating the net value of a life at 35 years of age at $50 per annum, he places the money loss at $240,000,000 per annum. Dublin and Whitney in the study just cited estimate the net value of a human life at $100 per annum, and conclude that the annual money loss from deaths is over $500,000,000. Dr.

2 John B. Huber, Consumption and Civilization, p. 89.
2 Publications American Statistical Association, December, 1920.

H. W. Thomas of Chicago has computed in greater detail the total money loss for Illinois from this cause. The loss from raising children who die of tuberculosis under the age of 20, is $1,187,800. The loss from inability to perform labor on the part of the consumptive is $30,000,000. The loss of savings of those who die before the end of the producing age is $5,139,000, and the cost of care of the sick is $225,000. This makes a total cost to Illinois yearly of $36,551,000. Looking at the matter from this point of view the cost of eliminating deadly diseases would be small compared with the losses incurred by their ravages. The total amount spent in the United States for the prevention of tuberculosis was estimated at $14,450,000 2 in 1911.

Although tuberculosis is the most serious single disease that attacks the human race, diseases due to other parasites complicate the situation, for each presents a separate problem of control. Pneumonia, influenza, cancer, and syphilis may be mentioned as some of the most serious germ diseases still prevalent. Smallpox, yellow fever, scarlet fever, diphtheria, and typhoid are among those which are gradually yielding to the progress of science, as shown by decreased death rates for them. Taken as a whole the struggle of man against lower organisms is one of his greatest problems, and the attainment of definite supremacy over these enemies will be of inestimable advantage to the human race.

The Indirect Struggle of Man with Lower Forms of Life. The indirect struggle of man with lower organic life is of the same general nature as the direct. While ordinarily its results are not quite so serious, it may lead to injuries similar in kind. The struggle concerns chiefly the innumerable pests which attack man's food supply. Vegetable products suffer from insects; such as the corn root-worm, and the chinch bug, which damage corn crops; the Hessian fly, which attacks the wheat crop; and insect scales and worms, which infect trees and fruits. Animals are injured by the bites of flies and ticks. Kelsey says that some two hundred insects attack domestic animals in this coun

1 John B. Huber, Consumption and Civilization, p. 90.
2 The survey, 27: 1612.

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try. Important raw materials also are liable to extensive damage. Enormous losses in the cotton crop have been caused by the boll weevil, the boll worm, and the cotton leaf worm. An estimate given below, of the total losses from pests, has been made by C. L. Marlott:

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Although it cannot be expected that all losses to crops will be avoided, a loss of over 10%, amounting in value to $800,000,ooo, can and should be greatly reduced. A saving of this amount would be more desirable than the addition of 10% to our cultivated land area, for a saving in crops already sown, and sometimes already harvested, would mean a saving of labor now expended without result. To increase crops 10% would involve more than a 10% increase in labor, for the extra supply would have to be raised on the margin of cultivation at the highest labor costs.

In addition to these comparatively regular losses there are occasional losses in particular districts from such plagues as grasshoppers, which often do enormous damage. In the tropics ants are a serious menace, for they destroy clothing and all but the very hardest woods, so that houses, utensils, and even railroad ties last there but a short time.

1 Year Book of the Department of Agriculture, 1904, p. 464.

Although insects are the most serious menace to crops because of the difficulty of their control, an astonishing amount of damage is done by larger animals. Mr. W. B. Bell,' an expert in the Department of Agriculture, estimated that prairie dogs, ground squirrels, pocket gophers, jack rabbits, and similar pests were cutting down the crops on farms in the western states, ten, twenty, and even thirty per cent; and were reducing the carrying capacity of pasture ranges ten to fifty per cent. It has been estimated also that native rodents cause a loss of $150,000,000 a year in cultivated crops, and a similar loss in forage on pasture ranges, or a total of $300,000,000 annually. House rats and mice are some of our worst enemies. They destroy annually $200,000,000 worth of crops and stored products. And, besides, rats are very dangerous disease carriers.

While our indirect struggle with lower animals is chiefly for vegetable products, the attacks of wild animals upon domestic animals occasion greater losses than is generally realized. Mr. Bell estimates that such animals as wolves, coyotes, bobcats, and mountain lions destroy from $20,000,000 to $30,000,000 worth of domestic stock annually.

Exceptional damage to crops may result in such a shortage as to create famine; and then the increasing death rate has results similar to those from the direct attacks of parasites. Advanced nations reduce this damage to a minimum by a diversity of crops. If one fails others may be substituted, and severe famine is usually avoided.

The Utilization of Lower Forms of Life. The utilization, or the domestication, of plants and animals took place at a very early period and has been of enormous consequence in the progress of civilization. Morgan 2 says that the domestication of animals took place in the middle status of barbarism, but some use was evidently made of animals long before that period.

1 Year Book of the Department of Agriculture, 1920. 2 Ancient Society, Ch. 1.

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