Boas, Franz. Race, Language and Culture – T10

[Race]

Growth

Early studies of growth have proved that from birth on the rate
of the absolute value of growth of the body as a whole is decreasing
until shortly before adolescence, and that at this time a rapid increase of
the rate of growth develops which lasts for a few years. It is followed
by a decrease which continues until the maximum stature is attained.
Bowditch, 11 Peckham 22 and Roberts, 33 who made these early studies also
showed that the distribution of statures and weights were asymmetrically
distributed. In 1892 I investigated these asymmetries and showed that
they were probably due to the changing rate of growth. I assumed that
the physiological development of children did not proceed at the same
rate, that some might be retarded, others accelerated and that their
physiological status would be distributed symmetrically according to
the laws of chance. This would result in an asymmetrical distribution
of statures. 44

William Townsend Porter's 55 measurements of St. Louis children
showed that children of a certain age in higher school grades were taller
and heavier than those of the same age in lower grades, and concluded
103that bright children grow more rapidly than dull ones. In reviewing his
results I wrote as follows. 16

I should prefer to call the less favorably developed grade of children
retarded, not dull; these terms are by no means equivalent, as a retarded
child may develop and become quite bright. In fact, an investigation
which I had carried on in Toronto with the same object in view, but
according to a different method, gives just the reverse result. The data
were compiled by Dr. G. M. West, who found that the children pronounced
by the teacher as bright were less favorably developed than
those called dull. Furthermore, I do not believe it is correct to say that
the facts found by Dr. Porter establish a basis of precocity and dullness,
but only that precocious children are at the same time better developed
physically; that is to say, the interesting facts presented by Dr. Porter
prove only that children of the same age who are found in higher grades
are more advanced in their general development than those found in
lower grades. Dr. Porter has shown that mental and physical growth
are correlated, or depend upon common causes; not that mental development
depends upon physical growth.

This brings me back to the question of the cause of the asymmetries
of the observed curves. According to the above interpretation of Dr.
Porter's results (which is merely a statement of the observed facts), we
must expect to find children of a certain age to be at different stages
of development. Some will stand on the point corresponding exactly
to their age, while others deviate from it. This was the assumption which
I made in the paper quoted above, when trying to explain the asymmetries
of the curves, and I consider Dr. Porter's observations a strong
argument in favor of my theory, which may be briefly summarized as
follows:

When we consider children of a certain age we may say that they will
not all be at the same stage of development. Some will have reached
a point just corresponding to their age, while others will be behind, and
still others in advance of their age. Consequently the values of their
measurements will not exactly correspond to those of their ages. We
may assume that the difference between their stage of development and
that belonging to their exact age is due to accidental causes, so that just
104as many will be less developed as further developed from the average
child of a particular age. Or, there will be as many children at a stage
of development corresponding to that of their age plus a certain length
of time as corresponding to that of their age minus a certain length of
time.

The number of children who have a certain amount of deviation in
time may be assumed to be arranged in a probability curve, so that the
average of all the children will be exactly at the stage of development
belonging to their age.

At a period when the rate of growth is decreasing rapidly, those children
whose growth is retarded will be further remote from the value
belonging to their age than those whose growth is accelerated. As the
number of children above and below the average of development is
equal, those with retarded growth will have a greater influence upon the
average measurement than those whose growth is accelerated, therefore
the average value of the measurement of all the children of a certain age
will be lower than the typical value, when the rate of growth is decreasing;
higher than the typical value when the rate of growth is increasing.
This shows that the averages and means of such curves have no meaning
as types. I have shown in the place quoted above, how the typical
values can be computed and also that for stature they differ from the
average up to the amount of 17 mm.

These considerations also show clearly that the curves must be asymmetrical.
Supposing we consider the weights of girls of thirteen years of
age, the individuals composing this group will consist of the following
elements: girls at their normal stage whose weight is that of the group
considered, advanced girls, and retarded girls. In each of these groups
which are represented in the total group in varying numbers, the weights
of the individuals are probably distributed according to the laws of
chance, or according to the distribution of weights in the adult population.
What, however, will be the general distribution ? As the rate of
increase of weight is decreasing, there will be crowding in those parts of
the curves which represent the girls in an advanced stage of development,
and this must cause an asymmetry of the resultant general curve,
which will depend upon the composition of the series. This asymmetry
does actually exist at the period when the theory demands it, and this
coincidence of theory and observation is the best argument in favor of
the opinion that advance and retardation of development are general
and do not refer to any single measurement.105

Furthermore, the increase in variability until the time when growth
begins to decrease, and its subsequent decrease, are entirely in accord
with this theory. I have given a mathematical proof of this phenomenon
in the paper quoted above (p. 103, note 4)… Dr. Porter's formulation
of the phenomenon, namely that “the physiological difference
between the individual children in an anthropometric series and
the physical type of the series is directly related to the quickness of
growth” does not quite cover the phenomenon.

It will be seen from these arguments that the very natural supposition
that some children develop more slowly than others is in accord with
all the observed facts. It was necessary to prove this in some detail
because the further interpretations made by Dr. Porter largely hinge
upon this point.

Another important phenomenon brought out in this paper is that
tall boys of 16 years grow much less than short boys, because they are
nearer the adult stage (Fig. 2).

From data collected in Worcester, Mass., 110 I proved that in early
years short children grow more slowly than tall children 211 (Fig. 3);
that is to say, their general development continues to be slow. Later on,
during the period of adolescence, they continue to grow, while tall children
have more nearly reached their full development. Small children
are throughout their period of growth retarded in development, and
smallness at any given period as compared to the average must in most
cases be interpreted as due to slowness of development. During early
life slowness of development which has manifested itself is likely to
continue, while some of the effects of retardation will be made good during
the period of adolescence, which is liable to be longer than in children
who develop rapidly in early life.

On account of these intricate relations between the amounts of growth
and stature attained at a given moment the percentile position of individuals
or of groups of individuals does not remain the same, but approaches
the average.

The results of this investigation suggest that the differences of growth
observed in children of different nationalities and of parents of different
occupations may also be partly due to retardation or acceleration
of growth, partly to differences in heredity.

In order to decide this question we may assume that in the averages
obtained for all the series representing various social groups only accidental
deviations from the general average occurred. Then it is possible
to calculate the average deviation which would result under these conditions.
When the actual differences that have been found by observation
are taken into consideration another average deviation results. If
the latter nearly equals the former, then the constant causes that affect
each social group are few and of slight importance. If it is much larger
than the former, then the causes are many and powerful. The ratio
between the theoretical value of the deviation and the one obtained by
observation is therefore a measure of the number and value of the causes
influencing each series.

I have applied these considerations to the measurements of Boston
school children obtained by Dr. H. P. Bowditch. I have used thirteen
different classes in my calculations, namely, five nationalities: American,
Irish, American and Irish mixed, German and English; and eight
108classes grouped according to nationalities and occupations: American
professional, mercantile, skilled labor and unskilled labor, and the same
classes among the Irish.

The observed and theoretical values are indicated in the following
diagram (Fig. 4).

The figures prove, therefore that
the differences in development between
various social classes are, to
a great extent, results of acceleration
and retardation of growth
which act in such a way that the
social groups which show higher
values of measurements do so on
account of accelerated growth, and
that they cease to grow earlier than
those whose growth is in the beginning
less rapid, so that there is
a tendency to decreasing differences between these groups during the
last years of growth.

The interpretation here given explains the simultaneous advance of
stature, weight, and school achievement. The question is of sufficient
importance to demand further corroboration. If the general development
affects all the traits of the body, being dependent upon physiological
age, we may expect that the correlation of measures during the
period of rapid growth is increased, because all are affected at the same
time in the same way. This was shown to be the case for school children
109of Worcester, Mass., and for selected years for those of Milwaukee and
Toronto 112 (Fig. 5).

The theory is finally proved by the determination of the tempo of
development as shown in the moments when certain physiological stages
are reached and by their variability. 116

As might be expected individual differences in the tempo of development
occur. Even children of the same family do not all develop at the
same rate. Some of these differences are hereditary, but others due to
outer conditions are at least equally important. Satisfactory nutrition
and absence of pathological processes accelerate growth. Poor nutrition
and frequent diseases retard it. Therefore we have to investigate in how
far individuals of the same population vary at various periods of life;
for instance, at what age the canines of individuals of the same group
erupt. The investigation of various events in the life of man which are
characteristic of certain age classes shows that the variability of the age
in which such an event takes place increases rapidly with increasing age.
For example, the period of pregnancy varies by a few days, the eruption
of the first deciduous tooth by a few months, puberty by more than a
year, and death by arteriosclerosis by more than ten years. The degree
of variability is expressed by the mean square deviation from the average
age. 217

tableau Male | Female | Difference | Pregnancy | Eruption of deciduous teeth | Lower central incisor | Lower molar 1 | Loss of deciduous teeth | Upper lateral incisor | Lower canine | Eruption of lower molar 2 | Ossification of hand | Presence of triquetrum | Presence of naviculare | Presence of pisiforme | Maximum rate of growth | Calcification of first rib 60% | Menopause

It appears from these data that the increase in variability of physiological
age is rapid until the fifth or sixth year. From the sixth to the
twentieth year it increases slowly. At a later age the increase is very
rapid.

I have described here the variability of the physiological development
as though the whole body were a unit. There are, however, differences
in the speed of development of various organs. This is brought out most
clearly by a comparison of the dates for eruption of teeth of boys and
girls. While in all other traits girls of a given age are much more mature
than boys of the same age, there are very slight differences only in the
eruption of teeth, proof that these are subject to influences different
from those acting upon the skeleton.

It is not admissible to assume with Crampton that physiological development
is equal to physiological age.

This appears in a comparison between growth and menarche. The
earlier the age of maximum growth, the longer is the interval between
this moment and the date of menarche. 219

tableau Age of Maximum Growth | Years | Average Interval between Date of Maximum Growth and Menarche | Months

A general comparison between the data for males and females shows
that the whole development of the female is more rapid than that of the
male. This brings about a curious relation between the measures of the
113two sexes. 120 It has been assumed that the sexes develop at approximately
the same rate until the prepubertal spurt of the girls sets in, about two
years before that of the boys. During this period stature and weight of
girls exceed those of boys and this lasts until the prepubertal spurt of
the boys begins while the girls are concluding their period of growth.

The best proof of the correctness
of this view is given by the peculiar
relation of the measures which
complete the principal part of their
growth at an early time. The
growth of the head offers a good
example. The total amount of increment
from the second year on is
slight. Therefore, if girls are ahead
of boys by one year and a half the
increment of growth corresponding
to this period is slight. If the typical difference between the sizes of
the sexes should be present during early childhood the heads of girls
ought to be smaller than those of the boys of the same age. This is
actually the case. The length of head of the adult woman is about 96%
of that of men. In childhood the length of head of girls is about 97.4%
of that of boys of the same age (Fig. 7). The ratio of 96% would be
found among girls chronologically three years younger than boys. 221 For
stature the normal relation of sizes of adult men and women is found for
girls chronologically one and a half years younger than boys which corresponds
to their physiological acceleration. The results of psychological
tests also show better results for girls than for boys of the same age,
which may also be due to a greater speed of development of girls.114

The general growth curve, being composed of individuals of markedly
different physiological stages becomes clearer when those having
the same physiological stage at some moment of their development are
segregated. I chose for this moment the time when the maximum rate
of growth of stature occurs, since this moment is in all probability most
closely related to the development of stature. The following curve shows
the growth of the various groups (Fig. 8).

It has been shown before that in these groups the increase in variability
which coincides approximately with the period of maximum
growth all but disappears.

A comparison of the rates of annual growth for those who have the
maximum rate of growth at the same time, during the periods preceding
and following that moment, show that development proceeds the more
rapidly the earlier it sets in (Figs. 9, 10).

This is also indicated by the total amount of increment during longer
periods preceding and following the moment of maximum rate of
growth, for example, during a period of 4½ years before and 4½ years
after this moment.

Unfortunately the available
data do not permit us
to follow the observation
up to absolutely completed growth. Some scanty data on boys of the
same social stratum who have been followed up to the completed adult
stage (Fig. 13) do not indicate that acceleration has any result on the
final stature, while the observations on girls followed up to 17 years on
which the data discussed above refer would indicate a slight effect. It
is exceedingly difficult to obtain data containing an adequate number
of continuous observations up to the adult stage.119

The variability of menarche is ± 1.6 years. According to this, girls
whose menarche is twice the variability, i.e., 3.2 years before the average
age, would be 3.2 × .96, or about 3 cm. shorter than those of average
physiological development. On the other hand stature in young years,
on account of its great variability, will have a much more marked
influence. The variability is approximately ±5.5 cm. Consequently
retarded individuals whose deviation from the norm is twice the variability,
i.e., 11 cm. too low, will be as adults 10.9 cm. shorter than the
average girl. In other words, what is presumably hereditary stature has
a much stronger influence than tempo of development.

At the same time the tempo of development does not depend entirely
upon environment. This has been demonstrated by our discussion
on pp. 86 et seq., which showed that familial traits influence the
rates of growth of brothers and sisters.

The general increase in stature which has been observed in every
part of Europe proves that non-hereditary influences affect the growth
of the body. Various studies have shown that children of parents living
under modern conditions exceed their parents in stature. The recent
study of the stature and other bodily measurements of Harvard students
compared with those of their own fathers 224 demonstrates this definitely.

A study of growing children of each age shows that those born in
recent years are taller than those born earlier. In order to avoid possible
errors I investigated the statures of the parents of immigrant children
contained in my report on Changes in Bodily Form of Immigrants. 325
These measurements were taken in 1909. The ages of the adults give,
therefore, at the same time the year of birth.

Figure 14 indicates merely the gradual decrease of stature with increasing
age. If there should be any increase with time of birth it would
be very slight. I think we may safely say that the stature of Hebrew
120immigrants has remained the same from 1845 to 1890. This corresponds
to the stability of their economic and social condition in Europe
during this period.

A comparison of a number of measures of adult Hebrews living in
America, mostly born in the United States, taken in 1909 and in 1937
shows also increases in all measures although not in equal proportional
amounts.

tableau Increase of Measures in Percent | Male [ Female | Stature | Length of head | Width of head | Width of face121

The influence of outer conditions upon growth may also be studied
by a comparison of various social strata. As an example I give the
statures of Hebrew children in an expensive private school compared
with the general East Side population of Hebrews, both series belonging
to the same period (Fig. 16).

The results of the measurements of children at entrance are given in
Figure 18.

It will be seen that the children placed in charge of the Hebrew
Orphan Asylum before 1918 were, at the time of admission, shorter
than those admitted after 1918.124

Racial determinants of growth curves are difficult to determine on
account of the strong environmental influences that affect growth. The
tempo of growth seems to be little affected by racial descent, but depends
rather upon environment. The average time of maturity of girls in New
York is practically the same for North Europeans and Hebrews. 127126

tableau Horace Mann School | Non-Hebrew | Hebrew | Hebrew Orphan Asylum | Italian Public School | Negro Orphan Asylum | Girls

A comparison of Negro and White in New York shows that the time
of adolescence and of the period of maximum rate of growth coincide,
or at least, that the difference in period is very slight. As among the
Whites, the earlier the period of maturation the more intense is the
129growth (Fig. 22). 129 Besides this we find that on the average the intensity
of growth among the Negroes is greater than among the Whites. It is
not possible to decide whether this is a racial characteristic or due to
environmental factors (Fig. 23).

The total growth curve of Negro orphan girls agrees with that of
other groups growing up under unfavorable conditions (Fig. 24).130