While practically nothing is known of the physiology of the Eskimo, with the exception of their great capacity for animal food, recent investigations have yielded definite information in this line regarding the Indians. It has been supposed that in his physiologic functions the Indian differs considerably from the white man, but the greater our knowledge in this direction the fewer the differences appear; there is, however, a certain lack of uniformity in this respect between the two races.
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The period of gestation of Indian women is apparently the same as that of the whites, and the new-born child is in every way comparable to the white infant. It begins to suckle as soon as it is given the breast, generally shows excellent nutrition, and has from the beginning a good voice. In 6 to 8 months the first teeth appear; during the 7th or 8th month the child begins to sit up; at 1 year it stands alone, and soon after begins to walk; at the age of about 18 months it commences to talk, and when 4 years of age it has a good command of language. During its first year the Indian child spends as much time in sleeping as does a healthy white child, and after the first year is very playful. It cries, on the average, less than the white child, but the principal reason for this seems to be the fact that it is generally well nourished and not sickly. The infant is nursed usually much later than among whites, not infrequently up to its 3d or 4th year, but after its 6th to 9th month it also partakes of most of the foods of its parents. Up to the 7th year incontinence of urine is quite frequent, apparently without pathological cause, but this disappears spontaneously thereafter.
As among whites, the period of puberty in the Indian is earlier in the low and hot regions than in those that are elevated or cold. In such very hot regions as the lower Colorado valley many of the girls begin to menstruate between the ayes of 11 and 13; while among tribes that live at a considerable altitude, as the Apache of Arizona and the Indians farther N., this function begins usually during the 13th or 14th year, and delays are more numerous; precise data from many localities are as yet lacking. The development of the breast in the girl commences usually at about the 12th year, and except among individuals there appears to be no great variation among the tribes of which there is most knowledge. Full development of the breast is seldom attained in the unmarried young woman before the 18th year. The time of puberty in Indian boys differs apparently but little, if any, from that in whites. Scanty growth of mustache is noticeable from about the 16th year, sometimes much later.
Marriage is generally entered into earlier than among American whites; only few girls of more than 18 years, and few young men of more than 22 years, are unmarried. Now and then a girl is unmarried at 14 or 15, and there is an instance of a Comanche girl of 11 years who married a Kiowa. Among the latter tribe it is not exceptional for girls to be married at 13. Indian women bear children early, and the infants of even the youngest mothers seem in no way defective. The birth rate is generally high, from 6 to 9 births in a family being usual. Twins are not very uncommon, but triplets occur very rarely. One or more naturally sterile women may be met in every large band.
The adult life of the Indian offers nothing radically different from that of ordinary whites. The supposed early aging of Indian women is by no means general and is not characteristic of the race; when it occurs, it is due to the conditions surrounding the life of the individual. stray hairs in small numbers may occasionally be found, as in brunette whites, even in children, but such occurrence is without significance. Senile grayness does not commence earlier than among healthy whites, and it advances more slowly, seldom, if ever, reaching the degree of complete whiteness. Baldness not due to disease is extremely rare. A common phenomenon observed in the aged Indian is pronounced wrinkling of the skin of the face and other parts. Little is known as to the exact period of menopause in the women, for but few of them know their actual age. Men remain potent, at least occasionally, much beyond 50 years. The longevity of the Indian is very much like that of a healthy white man. There are individuals who reach the age of 100 years and more, but they are exceptional. Among aged Indians there is usually little decrepitude. Aged women predominate somewhat in numbers over aged men. Advanced senility is marked by general emaciation, marked wrinkling of the skin, forward inclination of the body, and gradual diminution of muscular power as well as of acuteness of the senses. The teeth are often much worn down, or are lost mainly through the absorption of the alveolar processes.
Among the more primitive tribes, who often pass through periods of want, capacity for food is larger than in the average white. Real excesses in eating are witnessed among such tribes, but principally at feasts. On the reservations, and under ordinary circumstances, the consumption of food by the Indian is usually moderate. All Indians readily develop a strong inclination for and are easily affected by alcoholic drinks. The average Indian ordinarily passes somewhat more time in sleep than the civilized white man; on the other hand, he manifests considerable capability for enduring its loss, Yawning, snoring, eructation, and flatus are about as common with Indians as with whites. Sneezing, however, is rare, and hiccough even more so. Dreams are frequent and variable. Illusions or hallucinations in healthy individuals and under ordinary conditions have not been observed. Left handedness occurs in every tribe, and with nearly the same frequency as among whites (approximately 3 per cent). The sight, hearing, smell, and taste of the Indian, so far as can be judged from unaided but extended observation, are in no way peculiar. In the ordinary Indian with healthy eyes and ears, the sight and hearing are generally very good, but in no way phenomenal. To those who receive education above that of the common school, glasses are often necessary. In the old, eyesight is generally weakened, and in some the hearing is more or less blunted. The physical endurance of Indians on general occasions probably exceeds that of the whites.
The Indian easily sustains long walking or running, hunger and thirst, severe sweating, etc.; but he often tires readily when subjected to steady work. His mental endurance, however, except when he may be engaged in ceremonies or games, or on other occasions which produce special mental excitement, is but moderate; an hour of questioning almost invariably produces mental fatigue. Respiration and temperature are nearly the same as in healthy whites, the latter perhaps averaging slightly lower; but the pulse is somewhat slower, the general average in adult men approximating 66. Muscular force in the hands, tested by the dynamometer, is somewhat lower than with whites in the males and about equal in the females. The shoulder strength shows less difference, and the strength, or at least the endurance, of the back and lower limbs, judging from the work and other pursuits to which the Indians are accustomed, probably exceeds that of the whites.
The mental functions of the Indian should be compared with those of whites reared and living under approximately similar circumstances. On closer observation the differences in the fundamental psychical manifestations between the two races are found to be small. No instincts not possessed by whites have developed in the Indian. His proficiency in tracking and concealment, his sense of direction, etc., are accounted for by his special training and practice, and are not found in the Indian youth who has not had such experience. The Indian lacks much of the ambition known to the white man, yet he shows more or less of the quality where his life affords a chance for it, as in war, in his games, art, adornment, and many other activities.
The emotional life of the Indian is more moderate and ordinarily more free from extremes of nearly every nature, than that of the white person. The prevalent subjective state is that of content in wellbeing, with inclination to humor. Pleasurable emotions predominate, but seldom rise beyond the moderate; those of a painful nature are occasionally very pronounced. Maternal love is strong, especially during the earlier years of the child. Sexual love is rather simply organic, not of so intellectual an order as among whites; but this seems to be largely the result of views and customs governing sex relations and marriage. The social instinct and that of self-preservation are much like those of white people. Emotions of anger and hatred are infrequent and of normal character. Fear is rather easily aroused at all ages, in groups of children occasionally reaching a panic; but this is likewise due in large measure to peculiar beliefs and untrammeled imagination.
Modesty, morality, and the sense of right and justice are as natural to the Indian as to the white man, but, as in other respects, are modified in the former by prevalent views and conditions of life. Transgressions of every character are less frequent in the Indian. Memory (of sense impressions as well as of mental acts proper) is generally fair. Where the faculty has been much exercised in one direction, as in religion, it acquires remarkable capacity in that particular. The young exhibit good memory for languages. The faculty of will is strongly developed. Intellectual activities proper are comparable with those of ordinary healthy whites, though on the whole, and excepting the sports, the mental processes are probably habitually slightly slower. Among many tribes lack of thrift, improvidence, absence of demonstrative manifestations, and the previously mentioned lack of ambition are observable; but these peculiarities must be charged largely, if not entirely, to differences in mental training and habits. The reasoning of the Indian and his ideation, though modified by his views, have often been shown to be excellent. His power of imitation, and even of invention, are good, as is his aptitude in several higher arts and in oratory. An Indian child reared under the care of whites, educated in the schools of civilization, and without having acquired the notions of its people, is habitually much like a white child trained in a similar degree under similar conditions.
Consult Boteler, Peculiarities of the American Indian from a Physiological and Pathological Standpoint, 1880-81; Mays, Experimental Inquiry, 1887; Holder, Age of Puberty of Indian Girls, 1890; Currier, Study Relative to Functions of Reproductive Apparatus, 1891; Parker, Concerning American Indian Womanhood, 1891-92; Eleventh Census, Rep. on Indians, 1894; Hrdlicka (1) Physical and Physiological Observations on the Navaho, 1900, (2) Bull. 34, B. A. E., 1908. See also the bibliographies under Anatomy and Health and Disease.