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Boas, Franz. Race, Language and Culture – T08


Conditions controlling the tempo
of development and Decay 11

I venture to bring to your attention a number of observations
regarding the life span which I hope may be of interest to you.

The life span is usually understood to be expressed by tables of
expectation of life; but this is not what I mean to discuss. I wish to
exclude all deaths due to infections, contagious diseases and accidents,
and consider only the life span that we should find, if the strength of
the organism were allowed to exhaust itself and death were to occur as
a result of senility.

Even here certain allowances have to be made, for we may distinguish
between an hereditary, purely biologically determined element and
another one that depends upon conditions of life. Ample or deficient
nutrition, more or less exhausting daily labor, abuse of the body, greater
or lesser nervous strains are elements that modify the life span as it may
be determined by heredity. Even geographical conditions may have
their influence. Tropical or temperate climate, the degree of humidity,
altitude, all have their influence upon the life span. It is, therefore, impossible
to speak of the life span of an individual as determined absolutely
by hereditary constitution. It must always be understood as the
result of a hereditary constitution subject to a given set of environmental
conditions. Therefore, even in a population of the same descent, the
life span will depend upon social and economic conditions.

A closer examination of the problem shows that the simple statement
that a certain length of life may be expected for an individual of known
hereditary character and living in a known environment does not exhaust
it. The life span is the result of physiological processes that go
on throughout life and that have to be observed from the time of birth
until death. When we study the distribution of moments of the occurrence
of definite physiological changes, it appears that the variability of
the time of occurrence increases with great rapidity during life. Measured
89by standard variations, the period of pregnancy has a variability of
a few days, the appearance of the first teeth of a few weeks, the time
when puberty is reached varies by more than a year, the time of menopause
by several years, and death by arteriosclerosis by more than seven
years. These rapid increases are not the same for different types of
physiological phenomena. The teeth, for instance, behave quite differently
from the skeleton. All, however, show the characteristic rapid
increase in variability. This may be due to one of two causes. Either
the increase of variability may be due to a high degree of variability of
the changes which occur during a given interval without any relation
to the time when a previous stage is reached, or the given interval may
have a marked correlation with the time when the previous stage has
been reached. If the former is the case, it would be impossible to predict
the future, if the latter we may be able to predict the course of the life
span. It is, therefore, of fundamental importance for the understanding
of the life span to determine whether there is any correlation between
the rapidity of physiological processes during life.

Unfortunately it is very difficult without a somewhat rigid organization
to follow individuals from birth to death. Continuous observations
on individuals are most easily obtained during school life, and I have
asked myself the question whether during youth there is any evidence
of a consistent speed of physiological changes. The observations show
clearly that such consistency prevails. Following young children of six
years up to maturity it may be observed that growth is completed earlier
for tall ones than for short ones, both for boys and girls. During
adolescence all children show a decided increase in the speed of development.
Among girls this occurs earlier than among boys. This sudden
spurt is followed by a rapid decrease in the rate of growth. Among
young children, those who are tall have the spurt earlier than those who
are short. Tall girls have their first menstruation, on the average, earlier
than short ones. The criterion of size of young children is not as clear
as might be desired, because some children are tall because they are
accelerated in development, others are tall because by heredity they
belong to a tall strain. It is, therefore, more instructive to compare all
those who have the period of maximum rate of growth at the same time.
Then it appears that the whole growth period for those who mature
early is condensed. 12 The bodily growth occupies a short period and
proceeds with great energy. The reverse is true of those with a late
90spurt. They develop slowly and the whole period of growth is extended.
The same observation may be made on girls arranged according to the
time when they reach maturity, but it is not quite so clearly defined,
because the relation between sexual maturity and bodily growth is more
indirect. It is, however, evident from all the material collected that the
period of bodily development is a unit which in some individuals proceeds
rapidly, in others slowly.

The next important question to be decided is whether this unity of the
rate at which the physiological life process runs on is determined by
heredity or by the influence of outer conditions. The latter may be
proved by a number of observations. Many investigators have shown
that the average stature of European populations has increased considerably
since the middle of the past century. Previous studies do not
show us how this change comes about, whether it is a result of speeding
the process of development and of an incidental final increase, or
whether it is a general rise of the standards for each age. So far as the
material collected to date allows us to judge, there is a speeding up of
growth which brings about very great differences during the growth
period. These differences decrease when growth begins to slow up,
but result in a somewhat higher stature of the adult. The groups compared
were measured, the one in 1909, the other in 1935. It would
seem that the changed conditions result in a change of the tempo of
development. In other words, we find here proof that the tempo of
the life cycle in youth may be strongly modified by conditions of life.
I do not venture to speculate on the causes that may underlie these
changes, for it is not apparent that the social and economic conditions
of the groups concerned have changed noticeably during the interval of
twenty-five years. The only other series known to me is one of measurements
of children in Jena 13 in Germany; one taken from 1878-1880, the
other in 1921. This shows also a considerable increase in stature among
the children measured in 1921 notwithstanding the malnutrition of the
preceding years. It is not convincing because during the interval Jena
had become an industrial center which attracted people from a distance.
Since the native Thuringian population is markedly short, that of the
wider environment taller, I was inclined to ascribe the difference to the
differing ancestry of the two series. The phenomenon observed here in
New York in a more homogeneous group indicates, however, that conditions
91similar to those prevailing here may have contributed to the
increase in stature.

These observations conform with the experimental results of observations
on rats. Between 1912 and 1919 Gudernatsch 14 administered
dried endocrine glands to successive generations of white rats. He observed
that the feeding of dried thymus gland brought it about that the
animals treated were healthy, had numerous pregnancies, large litters
and long life. Recent work by L. G. Rowntree, J. H. Clark, and A. M.
Hanson 25 showed that injections of thymus extract (Hanson) accelerated
the rate of growth and development, hastened the onset of adolescence
in the offspring of the treated rats and increased the fertility of
parent rats. It is still more interesting to note that the acceleration is
much greater in later litters of the second generation and is more
marked in each succeeding generation under treatment. Omission of
the injection in one generation caused the loss of all these changes.
Analogous observations were made by Dr. Otto Roth. 36 There is still
some doubt as to the active principle that causes the acceleration. Both
the experiments on rats and the observations on man show clearly that
the tempo of development and the ultimate size may be influenced by
outer conditions.

Nevertheless, the importance of hereditary determinants may not be
neglected. Many attempts have been made to investigate the correlations
between the ages at death of parents and children, and it has
been found that a fairly marked positive correlation exists. The same
is true for members of a fraternity. The material is not quite convincing
because it is difficult to eliminate complex social causes and to confine
the cases strictly to death due to senile degeneration. I have investigated
the question in how far the tempo of development of one member of a
fraternity may be repeated among other members of the same fraternity.
The data prove that a child tall for its own age will have brothers
and sisters who mature early, while others who are short for their own
age will have such of a slow tempo of development. These data are
from an orphan asylum, where all the children were under the same
environmental conditions, so that external influences, if any, were very
slight. This also agrees with observations made on animals. Pearl 47 particularly
92has raised from a mixed series strains differing materially in
life span.

All these observations may be summarized in the statement that each
individual has by heredity a certain tempo of development that may be
modified by outer conditions. The gross, generalized observations available
at the present time suggest that in a socially uniform group the
tempo of development may be considered as an hereditary characteristic
of individuals.

The data which we have at our disposal end with the completion of
growth and the important question arises whether the characteristic
tempo of the individual extends over later periods of life ; whether a
rapid tempo of growth will also be associated with rapid decay and
earlier death, or whether other types of relation exist. Unfortunately it
is quite impossible at the present time to obtain adequate data which, as
you will readily observe, must be based on long continued observations
of the same individual. If we can obtain the cooperation of the proper
authorities such data might easily be secured from the officer corps of
the Army and Navy and in similar organizations that require periodic
health examinations.

We owe the knowledge of data in regard to later life to Dr. Felix
Bernstein 18 who proved by means of life insurance records that an early
onset of presbyopia is associated with other early degenerative processes
which lead to an earlier death by arteriosclerosis. I do not doubt that
many records of death in the archives of life insurance companies
could by appropriate search be associated with the growth curves of
individuals. Private schools which keep such records remain in touch
with their graduates, and by means of proper organization, policyholders
among them could be found in sufficient number to give the required
information. Furthermore, since we know that the tempo of development
is hereditary we might investigate the degree of presbyopia among
the parents of children whose growth curve is known. This might also
be secured with the help of private schools.

The general problem of the tempo of physiological processes in relation
to the life span is certainly not only of theoretical interest, but may
also enable us to predict with increased accuracy the expectation of life
even in early years.93

11 Read at the 46th Annual Meeting of the Association of Life Insurance Medical
Directors of America, October 17-18, 1935.

21 See p. 118.

31 Robert Rössle and Herta Böning, “Das Wachstum der Schulkinder,” Veröffentlichungen
aus der Kriegs- und Konstitutions Pathologie
, vol. 4, part 1 (1924).

41 Max Hirsch, Handbuch der inneren Sekretion (1930). Chapter: Entwicklung
und Wachstum.

52 Archives of Internal Medicine, vol. 56 (1935), no. 1, pp. 1-29.

63 Zeitschrift für Morphologie und Anthropologie, vol. 33 (1935), pp. 409-439.

74 See for instance “The Biology of Death VI,” The Scientific Monthly (1921),
pp. 143-162.

81 Zeitschrift für die gesammte Versicherungs-Wissenschaft, vol. 31 (1931), p. 150.