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If I venture to lay before you some brief remarks on the anthropological study of children, I do so for the reason that problems of hygiene are necessarily based on the consideration of the anatomical, physiological, and pathological conditions of masses of individuals, phenomena with which anthropological science is intimately concerned, for anthropology deals with the racial and social influences that determine form and function of the body, without reference to the peculiarities of the individual as such, although the range of variations in form and function in individuals who constitute a social group is a most important topic of our investigations. I wish to deprecate, therefore, at the outset all attempts at an individualistic interpretation of our results, which express only the general conditions that have to be considered in a study of the life of the individual, and which are modified in each individual by his peculiar life history and hereditary conditions that cannot be expressed in our generalized results. Nevertheless, the importance of these is great, for they express in a concise way the general effects of social and racial conditions that cannot be formulated in any other manner, and set definite problems to the student of hygiene as well as of anatomy and physiology.

The phenomena that interest us here are those of the development and growth of the child. The first attempt to study growth by metrical methods was made by Quetelet, in Belgium; but our first accurate knowledge is due to the investigations of Henry P. Bowditch, in Boston, and, later on, to those of Roberts, in England. These were followed by work on similar lines in America, Italy, Germany, France, Russia, and Japan. New lines of research were developed by the application of more rigid biometrical methods, the development of which we owe in large part to the influence of Francis Galton and to the work of Karl Pearson.

The results of these studies and the present status of the problem may be summarized as follows: The rate of growth of the body, measured by weight and stature, increases very rapidly until the fifth month of fetal life. From that time on the rate of growth decreases, first rapidly, then more slowly, until about four years before the age of puberty. During adolescence the rate of growth is considerably accelerated, and decreases again rapidly after sexual maturity has been reached. Thus the curve of growth represents a line which possesses a very high maximum at about the fifth month of fetal life. It decreases rapidly, and has a second although much lower maximum shortly before sexual maturity is reached, and not long afterwards reaches the zero point. The increase in bulk of the body continues much longer than that of length. In the beginning the rates of growth of the two sexes are about equal, that of the male probably exceeding slightly that of the female. Since, however, sexual maturity begins to develop earlier in the female than in the male, the concomitant acceleration also sets in at an earlier time, with the result that for a few years girls have a larger bulk of body than boys.

Although the periods of most active growth of the parts of the body differ considerably, it would seem that the characteristics of the curve of growth as here outlined are repeated in many if not in all organs and parts of the body. For instance, although the head reaches nearly its full size at an early time, so that its rate of growth shows a much more rapid decrease with age than that of the bulk of the body, there is an acceleration of growth during the period of adolescence. The differences between the sexes are in this case quite marked in early life, the head of the girl being always considerably smaller than that of the boy. The early prepubertal acceleration of the girl is not sufficient to bring the head measurements of girls up to those of boys, even during the prepubertal period. The difference in the measurement of the sexes is, therefore, not by any means solely due to the shorter period of development of girls, as might be supposed from a study of stature and weight alone, but important secondary sexual characteristics exist in early childhood.

These prove that the difference in physiological development between the two sexes begins at a very early time, and that in the fifth year it has already reached a value of more than a year and a half.

I give here a tabular statement of the available observations:

	Age in Years	Difference
	Boys	Girls
Ossification of scaphoid	5.8	4.2	-1.6
Ossification of trapezoid	6.2	4.2	-2.0
Eruption of inner permanent incisors	7.5	7.0	-0.5
Eruption of outer permanent incisors	9.5	8.9	-0.6
Eruption of bicuspids	9.8	9.0	-0.8
Minimum increase of annual growth	10.3	8.2	-2.1
Eruption of canines	11.2	11.3	+0.1
Maximum increase of annual growth	13.2	11.2	-2.0
Eruption of second molars	13.2	12.8	-0.4
Maximum variability of stature	14.8	12.4	-2.4

These data are not very accurate and must be considered a first approximation only.

When we remember that growth depends upon physiological development, it will be recognized that we must not compare the stature of girls of a certain age with that of boys of the same age, but that from the fourth year on a girl of a certain age should be compared with a boy a year and a half older than she is.

If this view is correct, then it appears that the relation in size of the two sexes persists even in childhood.

I think no better proof can be given of the correctness of this view than the peculiar behavior of those parts of the body which complete their growth at a very early time; for instance, that of the head.^[71] The total amount of the growth of the head from the second year on is slight. If, therefore, girls are ahead of boys in their development by about a year and a half or two years, the total amount of growth of the head in their favor will be the small amount of growth accomplished during this period of a year and a half or two years. If, then, there is a typical difference between the size of the body of male and female in childhood of the same character as found in adult life, then the head of the girl ought to be at all periods smaller than the head of the boy; and this is what actually happens. The phenomenon has been interpreted as indicating a less favorable development of the head of the woman; but the previous remarks show that it is obviously due solely to the different rate of physiological development of the two sexes. The results of physiological tests which show very generally that girls do better than boys of the same age may be another expression of the general acceleration of their development.

While we may thus speak of a curve of growth and development of the whole body and its organs, which has characteristic values for each moment in the life of the totality of individuals that compose a social group, not all the individuals pass through these stages of development with equal rapidity. It is easiest to make these conditions clear to ourselves by stating the various ages at which certain points in the physiological development of the individual are reached. Data are available for the periods of pregnancy, eruption of teeth, pubescence, sexual maturity, and development of long bones. So far as these can be reduced according to fairly accurate methods, the following results have been obtained: The average period of pregnancy is 269.4 days. One-fourth of all the children observed have been born in the periods of pregnancy between 265 and 273 days, one-half, between 260 and 278 days, and three-fourths, between 254 and 285 days. According to the laws of large numbers, the ratio of children born between any other limits of time can be determined, if any one of the pairs of values here mentioned is known; for instance, the pair which indicates the limits in which the middle half of all the children are born. In our case these limits are, accurately speaking, 269.4 days (the average), plus and minus 9 days. We may, therefore, call 9 days the measure of the variability of the period of pregnancy. I repeat that this means that one-half of all the children are born within the period limited by 269.4 days (the average), minus 9 days (i.e., 260.4 days), and plus 9 days (i.e., 278.4 days). In this way the variabilities shown in table on page 98^[72] have been determined.

It appears, from this table, which may be represented in the form of a curve, that the variability of the physiological stages of development increases very rapidly, probably so that its logarithm is in a ratio approximately proportional to the actual age, or, to use the term applied by Dr. Crampton and Dr. Rotch, to the chronological age. The causes that lead to this rapidly increasing variability are so far entirely unknown. It is certain, however, that there must be definite causes at work which bring about this phenomenon; for, if the variability were due to accidental causes only, it would increase much more slowly than in a ratio proportional to the increasing age, namely, proportional to its square root. The study of the general curve indicating the increase of variability in physiological development points to an irregularity at the time of approaching maturity. At this period the variability seems to increase at an unusually rapid rate, and either to be stationary or to decrease again at a later time.

	Age	Variability
	(years).	(years).
Pregnancy	0.0	± 0.09
First incisors	.6	± .14
First molars	1.6	± .20
Inner permanent incisors, girls	7.0	± 1.10
Inner permanent incisors, boys	7.5	± .90
Outer permanent incisors, girls	8.9	± 1.40
Bicuspids, girls	9.0	± 1.90
Outer permanent incisors, boys	9.5	± 1.40
Bicuspids, boys	9.8	± 1.10
Permanent canines, boys	11.2	± .90
Permanent canines, girls	11.3	± .70
Appearance of pubic hair, boys (Boas)	12.7	± 1.60
Second molars, girls	12.8	± 1.10
Second molars, boys	13.2	± 1.30
Appearance of pubic hair, boys (Crampton)	13.4	± 1.00
Full development of pubic hair, boys (Boas)	14.6	± 1.10
Full development of pubic hair, boys (Crampton)	14.5	± .90
Puberty, girls	14.9	± 1.30
Wisdom teeth, boys	19.3	± 1.40
Wisdom teeth, girls	22.0	± 1.20
Menopause	44.5	± 3.90
Death due to arterial diseases, men	62.5	± 8.80

I have spoken here of the variability of the physiological development of the body as though this were a unit. In 1895, in a discussion of Porter’s observations on the growth of school children in St. Louis, I pointed out the fact that a general variability in physiological development accounts for the close correlation between the distribution of children of the same age in school grades and the variations in the size of the body and its organs; and this problem was later on worked out by myself and Dr. Clark Wissler in regard to various measurements. These correlations have also been proved in a most interesting manner by Dr. Crampton’s observations on pubescence, and by Dr. Rotch’s study of the development of the epiphyses. It is true that a close correlation between the states of the physiological development of the various parts of the body exists, but there exists also a certain amount of variability in the development of one organ when another one has reached a certain definite stage. The correlation is so close that the condition of the bones, or that of pubescence, gives us a better insight into the physiological development of the individual than his actual chronological age, and may therefore be advantageously used for the regulation of child labor and school entrance, as Dr. Rotch and Dr. Crampton advocate; but we must not commit the error of identifying physiological development with physiological age, or of considering chronological age as irrelevant.

The clearest proof that is available is found in the data relating to increase of stature, and in observations on pubescence made according to Dr. Crampton’s methods. Bowditch was the first to investigate the phenomenon of growth of individuals who are short or tall at a given age, but his method was based on a statistical error. Later on, I showed that retarded individuals possess a late acceleration of growth, and these results were amplified by studies made by Dr. Beyer and Dr. Wissler. Recently I had occasion to make a more detailed statistical analysis of the phenomenon of growth,^[73] which shows that groups whose prepubertal accelerated growth begins late in life have rates of growth that exceed by far those of the normal individual; in other words, that, among the retarded groups, the whole energy required for growth is expended in a very brief period. In the case of stature, the phenomenon is complicated by the great differences in hereditary stature among the various parts of the population. It appears more clearly in observations on pubescence. Thus it can be shown that, if the first pubic hair appears in one group of boys at 11½ years, and in another at 15½ years, it will take the former much longer than the latter to attain the full development of pubic hair, and the rate of change found among them will be much greater than that of normally developed individuals. In other words, individuals who exhibit the same stages of physiological development are not the same, physiologically speaking, if their actual chronological ages differ; their past is not the same, and prospective physiological changes in their bodies will proceed in different ways. It is clear, therefore, that the greater the retardation or acceleration in any one particular respect, the greater also will be the disharmonies that develop in the body, since not all the other organs will follow the same rate of acceleration and retardation. The causes of these phenomena are unknown, but we may perhaps venture on the hypothetical explanation that all the cells of the body undergo certain progressive changes with increasing age, and that the internal secretions which become active at the time of puberty exert a stimulus upon the cells which causes accelerated growth in the cells, which depends, however, also upon the state of development of these cells. This may refer to the whole body, as well as to the glands that have a direct influence upon the rate of growth. In retarded individuals many of the cells have advanced in their development more nearly normally than the groups of cells involved in sexual maturity; and when their action sets in the cells of the body are stimulated much more vigorously than the less developed ones of an individual that reaches maturity at an earlier time. This hypothesis, however, would have to be tested experimentally. It is intended only to bring nearer to our understanding the complicated phenomena of retarded and accelerated growth.

It seems very likely that the abnormally large amount of energy expended upon rapid growth during a short period is an unfavorable element in the individual development. A study of the phenomena of growth of various groups of the same population has shown that early development is a concomitant of economic well-being, and that for the poor the general retardation in early childhood and the later accelerated growth are characteristic. It follows from this that there is a corresponding, although not equal, retardation in early mental development, and a crowding of developmental processes later on that probably places a considerable burden on the body and mind of the poor which the well fed and cared for do not suffer.^[74] The general laws of growth also show that a retardation kept up for an unduly long period cannot be made up in the short period of rapid growth; so that it would seem that, on the whole, excessive retardation is an unfavorable element in the growth and development of the individual. Whether there are similar disadvantages in a considerable amount of early acceleration is not so clear.

A word may also be said in regard to the evident increase in the general statures of the people of Europe, which has been proved by the study of military statistics. I presume this is partly due to better nutrition and earlier development, but it seems likely that much of it may be due to the better control of infantile diseases, which exert a long retarding influence upon the growth during the earlier years of childhood.

When we turn from the more general phenomena of growth to a consideration of their controlling causes, particularly of the influences of heredity and of environment, we have to confess our ignorance of the most elementary facts. While there is no doubt that the bodily size of the parents determines to a certain extent the growth of the bulk of the body of the children, it is not by any means clear in how far part of this may be due to the controlling effect of environmental causes to which parents and their children are equally subject. It is quite obvious that the earlier in fetal life certain traits are formed, and the earlier they reach their full development, the stronger will be the hereditary influence; while the later in life the full development is attained the greater will be the influence of environment, not only on account of the longer time of its action but also owing to the greater diversity of its form. Thus, if the anterior part of the palate has very nearly reached its final form and size in the sixth year no amount of subsequent change of food or use will materially influence its form; while weight and stature, and, even more, mental development, will be modified by the influences to which the individual is subject during the first two or three decades of his life. The problem of growth must, therefore, be studied for every organ independently.

Some observations have been made that illustrate the influence of environment, not only upon growth of the bulk of the body but also upon some of the forms that develop very early in life. Thus, it has been shown that urban and rural populations in Europe exhibit characteristic differences in size and form of the head. These differences are slight, and the attempt has been made to explain them as due to selection or mixture; but reasons can be brought forward that suggest other causes for the modification of the bodily forms. It has also been observed that a fairly homogeneous people like the East European Jews develop distinctive forms in the different parts of Europe that they inhabit, and that Italians, Bohemians, and Jews who come to America develop distinctive characteristics. Whatever the causes of these changes may be, whether due to selection or to internal changes brought about by the new environment, they indicate that heredity is not the sole factor that determines the development of the body.

The few observations which we possess on the growth of children of different races seem to show that there are definite characteristics of the growth curve for each group. Thus, Indian children seem to be shorter than European children, while the adult Indian is as tall as or taller than the European; but it is impossible to tell in how far this is due to the mode of life and how far to the influences of heredity. It is not too much to say that all the work on these problems remains to be done. Our ignorance of these facts should make us hesitate to judge rashly of the mental and bodily inferiority or superiority of races, since the data for forming a judgment are entirely lacking, and since most of the features on which we are accustomed to form our judgment develop late in life, and are therefore, as explained before, to a great extent subject to the influence of environment.

Related to these questions is the problem of the period of development of racial traits. At a very early stage of development children of all races are much alike, and many of the most characteristic traits do not develop until maturity is reached. Traces of these racial traits may be observed at an early time, but their accentuation occurs comparatively late. Here we have undoubtedly traits that are determined by a long line of ancestors, not by environment. Thus, parts of the body that are alike in childhood are subject to a more active growth in one race than in another. For instance, the elevation of the nose of the European, the prominence of the face of the Negro, the great length of the leg of the Negro, the great width of face of the Mongol and Indian are due to a marked growth of these features. Others, on the other hand, lag behind. Thus we are confronted with the ontogenetic problem of the origin of the diversity of human types, and of the oft-claimed but never-proved phenomena of early arrest of development in certain groups.

On the whole, what little we know would indicate that the periods of growth are the same everywhere, but that the rate of growth of various parts of the body is greater in one group than in another, and that in this manner the racial characteristics are developed. Too little is known, however, to express any definite opinion on this important subject.

The subject is one that, in its general aspects, as well as in the questions relating to the influence of heredity and environment, has a direct bearing upon questions of social well-being and upon our estimate of racial characteristics, and for this reason deserves systematic study, not only for the sake of its scientific interest but also on account of its practical importance.

[70]	Transactions of the 15th International Congress on Hygiene and Demography, held at Washington, D. C., September 23-28, 1912, (Washington, 1913).

[71]	See also p. 114.

[72]	Compare table on p. 112 in which the ages and standard variabilities for other features are given.

[73]	These observations, so far as stature is concerned, are contradicted by the data given on p. 118. I have not had an opportunity to check the observations on pubescence on new material.

[74]	This paragraph has to be revised in view of the contradictory observations mentioned in note 1, p. 99, and the discussions of tempo of growth pp. 86 et seq.