selection to explain the development of organic life, have adopted some form of the doctrine of orthogenesis. Evolution, according to this doctrine, has proceeded along definitely directed lines, and often without regard to utility. Nägeli, who was one of the most prominent advocates of orthogenesis, attributed evolution mainly to an internal "perfecting principle" which works, in obedience to certain definite laws, in causing organisms to become more highly developed. According to the orthogenesis of Eimer, on the other hand, evolution is due chiefly to inherited modifications produced by the environment. Eimer's orthogenesis, therefore, is essentially Lamarckism. The orthogenesists who appeal to internal causes in order to account for evolution have not been very explicit as to just what these internal causes are. Most forms of orthogenesis are statements as to how evolution has proceeded rather than why. What the causes of evolution may be is still a fertile field for speculation. We shall doubtless need to know much more about the fundamental processes of life than we do at present before the ultimate causes of evolution are revealed.

REFERENCES

CASTLE, W. E., COULTER, J. M., DAVENPORT, C. B., EAST, E. M., AND TOWER, W. L., Heredity and Eugenics. University of Chicago Press, 1912.

COPE, E. D., The Primary Factors of Organic Evolution. Chicago, Open Court Co., 1904.

DE VRIES, H., The Mutation Theory, 2 vols. Chicago, Open Court Co., 1909, 1910.

Species and Varieties: Their Origin by Mutation. Chicago, Open Court Co., 1905.

-, Plant Breeding. Chicago, Open Court, Co., 1907.

GATES, R. R., The Mutation Factor in Evolution. London, Macmillan, 1915.

KELLOGG, V. L., Darwinism To-day. N. Y., Holt, 1907.

MORGAN, T. H., Evolution and Adaptation. N. Y., Macmillan, 1903. Critique of the Theory of Evolution. Princeton University

SEWARD, A. C., Darwin and Modern Science. Cambridge University Press, 1909.

SPENCER, H., The Factors of Organic Evolution. N. Y., Appleton,

1887.

Principles of Biology (Rev. ed.), 2 vols. N. Y., Appleton, 1898, 1904.

CHAPTER XVIII

THE EUGENIC PREDICAMENT

We come now to a consideration of the evolutionary changes occurring in our own species, which is the most important phase of the whole problem of evolution, at least from our point of view. However high man may have risen above the rest of the animal creation, he is still an animal, remarkably similar in structure to his nearest anthropoid relatives, and remarkably like them also in his physiological functions and in his embryonic development. All the facts of human heredity are in harmony with the conclusion that our bodily and mental traits, like those of the lower animals, are transmitted in accordance with Mendel's law, and depend upon the same peculiarities of chromosome behavior. We are part and parcel of the animal creation, and it is fortunate that we are, because, through a study of the lower animals, we learn so very much that is enlightening in regard to ourselves. If all the controverted questions over the causes of evolution discussed in the last chapter were settled, it would be of great assistance to us in grappling with problems of the biological evolution of man. In fact, a very large part of the knowledge that has been gained concerning the life processes of human beings has been obtained by studying other creatures which stand below us in the scale of life.

When we look upon man as the final product of a long period of progressive development, we cannot help being led on to inquire if our present state is the highest which the human race will attain. The doctrine of evolution, which teaches that man has risen instead of fallen, leads us to look forward to the possibilities of further development, and to picture a race of human beings as superior to ourselves as we are superior to Neanderthal man, or his more apelike predecessors. But if we are entitled

to look down upon our poor cousins, the anthropoid apes, a candid contemplation of our physical and mental imperfections and infirmities will force us to admit that there is still a great deal of room for improvement. If one watches the stream of humanity as it files by on the streets of a large city he will readily admit that it would indeed be a pity were the great work of creative evolution to stop with no higher product than the rank and file of present-day humanity.

Francis Galton remarked that "our human civilized stock is

far more weakly through congenital imperfection than that of any other species of animals, whether wild or domestic." He was probably right. We have our hereditarily feeble-minded, epileptic, and insane, our hereditarily deaf and blind, our bleeders and albinos; and among the pathological characteristics transmitted by heredity may be mentioned cataract, cleft iris, displaced lens, cleft palate, harelip, atrophy of the optic nerve, progressive muscular atrophy, lack of teeth, abnormal hairiness of body, color-blindness, polydactylism, brachydactylism, fragility of bones, dwarfism, short sight, ichthyosis, chlorosis, cretinism, goiter, diabetes insipidus, and asthma. These are only a few of our hereditary, or partly hereditary ills. Among people whom we consider normal, there are marked hereditary differences in strength, endurance, and vitality. In some families the members are relatively shortlived, seldom living beyond fifty-five or sixty years of age. In other stocks the individuals exhibit an unusual toughness of constitution and frequently live into the nineties. It adds greatly

to one's expectation of life to come of long-lived ancestry on both sides.

In respect to its hereditary make-up, humanity is a motley lot. There is probably no other species whose inheritance is so exceedingly diversified. For centuries the inhabitants of different countries have been migrating into other realms and mingling their blood with that of alien peoples. The population of most civilized countries consists of mixtures of mixtures past all possibility of analysis or disentangling.

In a species so highly heterogeneous as our own, there is a

FIG. 225-Pedigree of hereditary cataract. The squares represent males, the circles females. (From Davenport and Laughlin.)

possibility of relatively rapid changes through selective breeding. If one could make the proper selection of parents for a few generations, it would not be difficult to bring about great changes in such characteristics as stature, complexion, color of eyes and hair, shape of head, and the degree of native intelligence. Even the most ardent eugenist does not propose that the mating of human beings should be arbitrarily regulated in the interest of their posterity. But if selective breeding were carried out in the human race, it would be easily possible to effect great changes for better or for worse in a comparatively short time.

When treating of the effects of artificial selection, it was pointed out that the rapid improvements main many species were mainly brought about by merely taking hereditary diversities already existing in the sto