CHAPTER VI!
!
!NATURAL SELECTION!
Man has risen
from the ape chiefly through the action of natural
!selection. Any
scheme of conscious race betterment, then, should carefully examine nature's
method, to learn to what extent it is still acting, and to what extent it may
better be supplanted or assisted by methods of man's own invention.
Natural
selection operates in two ways: (1) through a selective death-rate and (2)
through a selective birth-rate. The first of these forms has often been
considered the whole of natural selection, but
wrongly. The
second steadily gains in importance as an organism rises in the scale of
evolution; until in man it is likely soon to dwarf the
!lethal factor
into insignificance. For it is evident that the appalling slaughter of all but
a few of the individuals born, which one usually associates with the idea of
natural selection, will take place only when the number of individuals born is
very large. As the reproductive rate decreases, so does the death-rate, for a
larger proportion of those born are able to find food and to escape enemies.
When considering
man, one realises at once that relatively few babies or adults starve to death.
The selective death-rate therefore must include only those who are unable to
escape their enemies; and while these enemies of the species, particularly
certain micro-organisms, still take
!a heavy toll
from the race, the progress of science is likely to make it much smaller in the
future.
The lethal
factor is the one which Darwin himself most emphasised. Obviously a race will
be steadily improved, if the worst stock in it is cut off before it has a
chance to reproduce, and if the best stock survives to perpetuate its kind.
"This preservation of favourable individual differences and variations,
and the destruction of those which are injurious, I have called natural
selection, or the survival of the fittest," Darwin wrote; and he went on
to show that the principal checks on increase were overcrowding, the difficulty
of obtaining food, destruction by enemies, and the lethal effects of climate.
These causes may be conveniently divided into sustentative
!and
non-sustentative. The sustentative factor has acquired particular prominence in
the human species, since Malthus wrote his essay on population--that essay
which both Darwin and Wallace confess was the starting point of their discovery
of natural selection.
There is a
"constant tendency in all animated life to increase beyond the nourishment
prepared for it," Malthus declared. "It is incontrovertibly true that
there is no bound to the prolific plants and animals, but what is made by their
crowding and interfering with each
!others' means
of subsistence." His deduction is well known: that as man tends to
increase in geometrical ratio, and can not hope to increase his food-supply
more rapidly than in arithmetical ratio, the human race must eventually face
starvation, unless the birth-rate be reduced.
When the
non-sustentative forms of lethal selection are considered, it is seen very
clearly that man is not exempt from the workings of this law. A
non-sustentative form of natural selection takes place through the destruction
of the individual by some adverse feature of the environment, such as excessive
cold, or bacteria; or by bodily deficiency; and it is independent of mere
food-supply. W. F. R. Weldon
showed by a long
series of measurements, for example, that as the harbour of Plymouth, England,
kept getting muddier, the crabs which lived in it kept getting narrower; those
with the greatest frontal breadth filtered
!the water
entering their gills least effectively, and died.
But, it was
objected, man is above all this. He has gained the control
!of his own
environment. The bloody hand of natural selection may fall on crabs: but surely
you would not have us think that Man, the Lord of Creation, shares the same
fate?
!Biologists
could hardly think otherwise. Statisticians were able to supply the needed
proof. A selective death-rate in man can not only be demonstrated but it can be
actually measured.
"The
measure of the selective death-rate." says[53] Karl Pearson, to whom this
achievement is due, "is extraordinarily simple. It consists in the fact
that the inheritance of the length of life between parent and offspring is
found statistically to be about one-third of the average inheritance of
physical characters in man. This can only be due to the fact that the death of
parent or of offspring in a certain number of cases is due to random and not to
constitutional causes." He arrived at the conclusion[54] that 60% of the
deaths were selective, in the Quaker
families which
he was then studying. The exact proportion must vary in accordance with the
nature of the material and the environment, but as
!Ploetz found at
least 60% of the deaths to be selective in the European royal families and
nobility, where the environment is uniformly good, there is no reason to think
that Professor Pearson's conclusion is invalid.
!Dr. Ploetz[55]
investigated the relation between length of life in parents, and infant
mortality, in about 1,000 families including 5,500 children; half of these were
from the nobility and half from the peasantry. The results were of the same
order in each case, indicating that environment is a much less important factor
than many have been wont to suppose. After discussing Professor Pearson's work,
he continued:
It seems to me
that a simpler result can be reached from our material in the following way.
Since the greater child-mortality of each of our classes of children (divided
according to the ages at death of their parents) indicates a higher mortality
throughout the rest of their lives, the offspring of parents who die young will
therefore be eliminated in a higher degree, that is, removed from the
composition of the race, than will those whose parents died late. Now the
elimination can be non-selective, falling on all
sorts of
constitutions with the same frequency and degree. In that case it will of
course have no connection with selection inside the race. Or it may be of a
selective nature, falling on its victims because they differ from those who are
not selected, in a way that makes them less capable of resisting the pressure
of the environment, and avoiding its dangers. Then we speak of a selective
process, of the elimination of the weaker and the survival of the stronger.
Since in our examination of the various causes of the difference in infant
mortality, in the various age-classes of
parents, we
found no sufficient cause in the effects of the
!environment,
which necessarily contains all the non-selective perils, but found the cause to
be in the different constitutions inherited by the children, we can not escape
the conclusion that the differences in infant mortality which we observe
indicate a strong process of natural selection.
The infant
mortality with the 85-year-old fathers and mothers is found to be 11.2%-15.4%,
average about 13%. The total
child-mortality
reaches 31-32%, of which the 13% make about 40%. Accordingly at least 60%, and considering
the above mentioned sources of error we may say two-thirds, of the child
mortality is selective in character. That accords reasonably well with the
!55-74% which
Pearson found for the extent of selective deaths in his study.
!In general,
then, one may believe that more than a half of the persons who die nowadays,
die because they were not fit by by nature (i. e., heredity) to survive under
the conditions into which they were born. They are the victims of lethal
natural selection, nearly always of the non-sustentative type. As Karl Pearson
says, "Every man who has lived through a hard winter, every man who has
examined a mortality table, every man who has studied the history of nations
has probably seen natural selection at work."
There is still
another graphic way of seeing natural selection at work, by an examination of
the infant mortality alone. Imagine a thousand babies coming into the world on
a given day. It is known that under
average American
conditions more than one-tenth of them will die during the first year of life.
Now if those who die at this time are the
inherently
weaker, then the death-rate among survivors ought to be correspondingly less
during succeeding years, for many will have been cut down at once, who might
otherwise have lingered for several years, although doomed to die before
maturity. On the other hand, if only a few die during the first year, one might
expect a proportionately greater number to die in succeeding years. If it is
actually found that a high death-rate in the first year of life is associated
with a low
!death-rate in
succeeding years, then there will be grounds for believing that natural
selection is really cutting off the weaker and allowing the stronger to
survive.
C. Snow[56]
analysed the infant mortality registration of parts of England and Prussia to
determine whether any such conclusion was justified. Natural selection, in the
form of a selective death-rate, is strongly operative in man in the early years
of life. We assert with great
!confidence that
a high mortality in infancy (the first two years of
life) is followed by a correspondingly low mortality in childhood, and
vice-versa.... Our work has led us to the conclusion that infant mortality does
effect a 'weeding out' of the unfit."
"Unfitness"
in this connection must not be interpreted too narrowly. A child may be
"unfit" to survive in its environment, merely because its parents are
ignorant and careless. Such unfitness makes more probable an
!inheritance of
low intelligence.
Evidence of natural
selection was gathered by Karl Pearson from another source and published in
1912. He dealt with material analogous to that
of Dr. Snow and
showed "that when allowance was made for change of environment in the
course of 50 years, a very high association existed between the deaths in the
first year of life and the deaths in childhood (1 to 5 years). This association
was such that if the infantile
!death-rate
increased by 10% the child death rate decreased by 5.3% in males, while in
females the fall in the child death-rate was almost 1% for every 1% rise in the
infantile death-rate."
!To put the
matter in the form of a truism, part of the children born in any district in a
given year are doomed by heredity to a premature death; and if they die in one
year they will not be alive to die in some succeeding year.
Lately a new
mathematical method, which is termed the Variate Difference Correlation method,
has been invented and gives more accurate results,
in such an
investigation as that of natural selection, than any hitherto used. With this
instrument Professor Pearson and Miss Elderton have confirmed the previous
work. Applying it to the registered births in England and Wales between 1850
and 1912, and the deaths during the first five years of life in the same
period, they have again found[57] that
!"for both
sexes a heavy death-rate in one year of life means a markedly lower death-rate
in the same group in the following year of life." This lessened death-rate
extends in a lessened degree to the year following that, but is not by the
present method easy to trace further.
!"It is
difficult," as they conclude, "to believe that this important fact
can be due to any other source than natural selection, i. e., a heavy mortality
leaves behind it a stronger population."
To avoid
misunderstandings, it may be well to add to this review the closing words of
the Elderton-Pearson memoir. "Nature is not concerned with the moral or
the immoral, which are standards of human conduct, and the duty of the
naturalist is to point out what goes on in Nature. There
!can now be
scarcely a doubt that even in highly organised human communities the death-rate
is selective, and physical fitness is the criterion for survival. To assert the
existence of this selection and measure its intensity must be distinguished
from an advocacy of high infant mortality as a factor of racial efficiency.
This reminder is the more needful as there are not wanting those who assert
that demonstrating the existence of natural selection in man is identical with
decrying all efforts to reduce the infantile death-rate.”
The conclusion
that, of the infants who die, a large number do so through inherent
weakness--because they are not "fit" to survive--is also suggested by
a study of the causes of death. From a third to a half of the deaths during the
first year of life, and particularly during the first month, are due to what
may be termed uterine causes, such as debility, atrophy, inanition, or
premature birth. Although in many
!cases such a
death is the result of lack of prenatal care, in still more it must be ascribed
to a defect in the parental stock.
In connection
with infant mortality, it may be of interest to point out that the intensity of
natural selection is probably greater among boys than among girls. There is a
steady preponderance of boys over girls at birth (about 105 to 100, in the
United States), while among the stillborn the proportion is 158 to 100, if the
Massachusetts figures for 1891-1900 may be taken as general in application.
Evidently a large
number of weak
males have been eliminated before birth. This elimination continues for a
number of years to be greater among boys than among girls, until in the period
of adolescence the death-rates of the two
sexes are equal.
In adult life the death-rate among men is nearly always higher than that among
women, but this is due largely to the fact that men pursue occupations where
they are more exposed to death. In such cases, and particularly where deaths
are due to accident, the mortality may not only be non-selective, but is
sometimes contra-selective, for the strongest and most active men will often be
those who expose
themselves most
to some danger. Such a reversal of the action of natural selection is seen on a
large scale in the case of war, where the
!strongest go to
the fray and are killed, while the weaklings stay at home to perpetuate their
type of the race.
A curious aspect
of the kind of natural selection under
consideration,--that
which operates by death without reference to the food-supply,--is seen in the
evolution of a wide pelvis in women. Before the days of modern obstetrics, the
woman born with an unusually narrow pelvis was likely to die during
parturition, and the inheritance of a narrower type of pelvis was thus stopped.
With the introduction and
improvement of
instrumental and induced deliveries, many of these women are enabled to
survive, with the necessary consequence that their
daughters will
in many cases have a similarly narrow pelvis, and experience similar difficulty
in childbirth. The percentage of deliveries in which instrumental aid is
necessary is thus increasing from generation to generation, and is likely to
continue to increase for some time. In other words, natural selection, because
of man's
!interference,
can no longer maintain the width of woman's pelvis, as it formerly did, and a
certain amount of reversion in this respect is probably taking place--a
reversion which, if unchecked, would necessarily lead after a long time to a
reduction in the average size of skull of that part of the human race which
frequently uses forceps at childbirth. The time would be long because the
forceps permit the survival of some large-headed infants who otherwise would
die.
!But it must not
be supposed that lethal, non-sustentative selection works only through forms of
infant mortality. That aspect was first discussed because it is most obvious,
but the relation of natural selection to microbic disease is equally widespread
and far more striking.
As to the
inheritance of disease as such there is little room for misunderstanding: no
biologist now believes a disease is actually handed
down from parent
to child in the germ-plasm. But what the doctors call a diathesis, a
predisposition to some given disease, is most certainly heritable--a fact which
Karl Pearson and others have proved by
statistics that
can not be given here.[58] And any individual who has inherited this diathesis,
this lack of resistance to a given disease, is marked as a possible victim of
natural selection. The extent to which and the manner in which it operates may
be more readily understood by the study of a concrete case. Tuberculosis is, as
everyone knows, a disease caused directly by a bacillus; and a disease to which
immunity can not be acquired by any process of vaccination or inoculation yet
known. It is a disease which is not directly inherited as such. Yet
every
city-dweller in the United States is almost constantly exposed to infection by
this bacillus, and autopsies show that most persons have actually been infected
at some period of life, but have resisted
!further
encroachment. Perhaps a fraction of them will eventually die of consumption;
the rest will die of some other disease, and will probably never even know that
they have carried the bacilli of tuberculosis in their lungs.
Of a group of
men picked at random from the population, why will some eventually die of
tuberculosis and the others resist infection? Is it a matter of
environment?--are open-air schools, sanitary tenements, proper hygiene, the kind
of measures that will change this condition? Such is
!the doctrine
widely preached at the present day. It is alleged that the white plague may be
stamped out, if the open cases of tuberculosis are isolated and the rest of the
population is taught how to live properly. The problem is almost universally
declared to be a problem of infection.
!Infection
certainly is the immediate problem, but the biologist sees a greater one a
little farther back. It is the problem of natural selection.
To prove this, it
is necessary to prove (1) that some people are born with less resistance to
tuberculosis than others and (2) that it is these people with weak natural
resistance who die of phthisis, while their neighbours with stronger resistance
survive. The proof of these
propositions has
been abundantly given by Karl Pearson, G. Archdall Reid and others. Their main
points may be indicated. In the first place it
must be shown
that the morbidity from tuberculosis is largely due to heredity--a point on
which most medical men are still uninformed. Measurement of the direct
correlation between phthisis in parent and child shows it to be about .5, i.
e., what one expects if it is a matter
!of heredity.
This is the coefficient for most physical and mental characters: it is the
coefficient for such pathological traits as deafness and insanity, which are
obviously due in most cases to inheritance rather than infection.
But, one
objects, this high correlation between parent and child does not prove
inheritance,--it obviously proves infection. The family relations are so
intimate that it is folly to overlook this factor in
!the spread of
the disease.
Very well,
Professor Pearson replied, if the relations between parent and child are so
intimate that they lead to infection, they are
certainly not
less intimate between husband and wife, and there ought to be just as much
infection in this relationship as in the former. The correlation was measured
in thousands of cases and was found to lie around .25, being lowest in the
poorer classes and highest in the
!well-to-do classes.
At first glance
this seems partly to confirm the objection--it looks as
!if there must
be a considerable amount of tubercular infection between husband and wife. But
when it is found that the resemblance between husband and wife in the matter of
insanity is also .25, the objection becomes less formidable. Certainly it will
hardly be argued that one of the partners infects the other with this
disability.
As a fact, a
correlation of .25 between husband and wife, for tuberculosis, is only partly
due to infection. What it does mean is that like tends to mate with
like--called assortative mating. This coefficient of resemblance between
husband and wife in regard to phthisis is about the same as the correlation of resemblance
between husband and wife for eye colour, stature, longevity, general health,
truthfulness, tone of voice, and many other characters. No one will suppose
that life partners "infect" each other in these respects.
!Certainly no
one will claim that a man deliberately selects a wife on the basis of
resemblance to himself in these points; but he most certainly does so to some
extent unconsciously, as will be described at greater length in Chapter XI.
Assortative mating is a well-established fact, and there is every reason to
believe that much of the resemblance between husband and wife as regards
tuberculosis is due to this fact, and not to infection.[59]
!Again, it is
objected that the infection of children is not a family matter, but due to
tuberculous cows' milk: how then does it appear equally among the Japanese,
where cows are not tuberculous and cow's milk rarely used as an infant food: or
among such people as the Polynesians, who have never seen a cow?
But, it is
argued, at any rate bad housing and unsanitary conditions of life will make
infection easier and lower the resistance of
the individual. Perhaps such conditions may make infection easier, but
that is of little importance considering how easy it is for all city
!dwellers--for
the population as a whole. The question remains, will not bad housing cause a
greater liability to fatal phthisis? Will not destitution and its attendant
conditions increase the probability that a given individual will succumb to the
white plague?
Most physicians
think this to be the case, but they have not taken the pains to measure the
respective roles, by the exact methods of modern science. S. Adolphus Knopf of
New York, an authority on tuberculosis, recognises the importance of the
heredity factor, but says that after this, the most important predisposing
conditions are of the nature of unsanitary schools, unsanitary tenements,
unsanitary factories and
!workshops. This
may be very true; these conditions may follow after heredity in importance--but
how near do they follow? That is a matter capable of fairly accurate
measurement, and should be discussed with figures, not generalities.
Taking the case
of destitution, which includes, necessarily, most of the other evils specified,
Professor Pearson measured the correlation with liability to phthisis and found
it to be .02. The correlation for direct heredity--that is, the resemblance
between parent and offspring--it will be remembered, is .50. As compared with
this, the environmental factor of .02 is utterly insignificant. It seems
evident that whether or not
!one dies from
tuberculosis, under present-day urban conditions, depends mainly on the kind of
constitution one has inherited.
There is no
escape, then, from the conclusion that in any individual, death from tuberculosis
is largely a matter of natural selection. But by taking a longer view, one can
actually see the change to which natural selection is one of the contributors.
The following table shows
!
the deaths from
consumption in Massachusetts, per 10,000 population:
!
L. Hoffman
further points out[60] that in Massachusetts, Rhode Island,
!and
Connecticut, 1872-1911, the decline in the death-rate from tuberculosis has
been about 50%. "The evidence is absolutely conclusive that actually as
well as relatively, the mortality from tuberculosis in what is the most
intensely industrial area of America has progressively diminished during the
last 40 years."
!It will be
noted that the great increase in death from consumption in this area began in
the decade following 1840, when the large Irish immigration began. The Irish
are commonly believed to be particularly susceptible to phthisis. Crowded
together in industrial conditions, they rapidly underwent infection, and their
weak racial resistance led to a high death-rate.
That
tuberculosis is particularly fatal to the Negro race is well known. Even
to-day, after several centuries of natural selection in the United States, the
annual death-rate from consumption among Negroes in the registration area is
431.9 per 100,000 population (census of 1900) as compared with 170.5 for the
whites; in the cities alone it is 471.0.
That
overcrowding and climate can not be the sole factors is indicated by the fact
that the Negro race has been decimated, wherever it has met tuberculosis.
"In the years 1803 and 1810 the British government
imported three
or four thousand Negroes from Mozambique into Ceylon to form into regiments,
and of these in December, 1820, there were left
just 440,
including the male descendants. All the rest had perished mainly from
tuberculosis, and in a country where the disease is not nearly so prevalent as
in England."[61] Archdall Reid has pointed
out[62] that the
American, Polynesian and Australian aborigines, to whom tuberculosis was
unknown before the advent of Europeans, and who had therefore never been
selected against it, could not survive its advent:
!they were
killed by much smaller infections than would have injured a European, whose
stock has been purged by centuries of natural selection.
These racial
histories are the most important evidence available to the student of natural
selection in man. The conclusion to be drawn from them seems plain. Natural
selection, which has in the past never had an opportunity to act upon the Negro
race through tuberculosis, is now engaged in hastening, at a relatively rapid
rate, the evolution of this race toward immunity from death by tuberculosis.
The evolution of the white race on this line is, as the figures show, going on
simultaneously,
but having begun centuries earlier, it is not now so rapid. The weakest white
stocks were cut off hundreds of years ago, in Great Britain or Europe; those of
the black race are only now going.
Despite all the
efforts of medicine and sanitation, it is likely that
!the Negro death-rate
from phthisis will continue high for some years, until what is left of the race
will possess a degree of resistance, or immunity, not much inferior to that of
the whites among whom they live. The blacks in North America now must be
already more resistant than their ancestors; the mulattoes descended of normal
healthy unions should be more resistant than the pure Negroes, although no
statistics are available on the point; but were a new immigration to take place
from Africa to-day, and the immigrants to be put into villages with their
Americanised brethren, the high death-rate would result.
It is the custom
of sentimentalists sometimes to talk as if the North American Indian had been
killed off by the white man. So he was,--but not directly: he was killed off by
natural selection, acting through the white man's diseases and narcotics. In
1841 Catlin wrote, "Thirty millions of white men are now scuffling for the
goods and luxuries of life over the bones of twelve millions of red men, six
millions of whom have fallen victims to small-pox." Small-pox is an old
story to the white race, and the death of the least resistant strains in each
generation has left a population that is fairly resistant. It was new to the
natives of America, and history shows the result. Alcohol, too,
counted its
victims by the thousand, for the same reason. The process of natural selection
among the North American Indians has not yet stopped; if there are a century
from now any Indians left, they will of
!necessity
belong to stocks which are relatively resistant to alcohol and tuberculosis and
the other widespread and fatal diseases which were unknown upon this continent.
The decrease of
natives following the Spanish conquest of tropical America has long been one of
the most striking events of history. Popular historians sometimes speak as if
most of the native population had been killed off by the cruelty of the
conquistadores. Surely such talk could not proceed from those who are familiar
with the action of
natural
selection. It is obvious that when the Spaniard brought the
natives
together, making them work in mines and assemble in churches, he brought them
under conditions especially favourable for infection by the new diseases which
he had brought. The aborigines of the New World, up to the time the Spaniards
came, had undergone no evolution whatever against these diseases; consequently
the evolution began at so rapid a
!rate that in a
few centuries only those who lived in out-of-the-way places remain unscathed.
In Tasmania is
another good illustration of the evolution of a race proceeding so rapidly as
to be fatal to the race. When the first
English settled
on the island, in 1803, the native population consisted
of several
thousand. Tuberculosis and many other new diseases, and, most of all, alcohol,
began to operate on the aborigines, who were attracted
to the
settlements of the whites. In a quarter of a century there were only a few
hundred left. Many, of course, had met violent deaths, but an enlightened
perusal of any history of the period,[64] will leave no
!doubt that
natural selection by disease was responsible for most of the mortality. By 1847
the number of native Tasmanians was reduced to 44, who were already
unmistakably doomed by alcohol and bacteria. When the last full-blood Tasmanian
died in 1876, a new chapter was written in the story of the modern evolution of
the human race.
No such stories
are told about the white settlements on this continent, even before the days of
quarantine and scientific medicine. There is no other adequate explanation of
the difference, than that the two races have evolved to a different degree in
their resistance to these
!diseases. It is
easily seen, then, that man's evolution is going on, at varying rates of speed,
in probably all parts of the human race at the present time.
This long
discussion may now be summarised. We dealt with lethal selection, that form of
natural selection which operates by prematurely killing off the less fit and
leaving the more fit to survive and
!reproduce their
kind. It is of course understood that the word "fit" in this
connection does not necessarily mean morally or mentally superior, but merely
fit for the particular environment. In a community of rascals, the greatest
rascal might be the fittest to survive.
!Two forms of
lethal selection were distinguished, one depending on starvation and the other
on causes not connected with the food supply. Direct starvation is not a factor
of importance in the survival of most races during most of the time at the present
day so far as the civilised portion of the world is concerned. But disease and
the other lethal factors not connected with the food-supply, through which
natural selection acts, are still of great importance. From a half to
two-thirds of all deaths are of a selective character, even under favourable
conditions.
It is also to be
noted, however, that with the progress of medicine, and the diminution of unfit
material, this kind of natural selection will tend to become less and less
widespread. For a long time, natural
selection in man
has probably done little to cause marked change in his physical or mental
characteristics. Man's interference has prevented. In recent centuries natural
selection has probably done no more on the whole than keep the race where it
was: it is to be feared that it has
!not even done
that. It is doubtful if there is any race to-day which attains the physical and
mental average of the Athenians of 2,500 years ago.
!Lethal natural
selection, then, has been and still is a factor of great importance in the
evolution of the race, but at present it is doing little or nothing that
promises to further the ideal of eugenics--race betterment.
!But lethal
natural selection is only half the story. It is obvious that if the constitution
of a race can be altered by excess of deaths in a certain class, it can equally
be altered by excess of births in a certain class. This is reproductive
selection, which may appear in either one of two forms. If the individual
leaves few or no progeny because of his failure to mate at the proper time, it
is called sexual selection; if, however, he mates, yet leaves few or no progeny
(as compared with other individuals), it is called fecundal selection.
!While the
reproductive rate must be looked upon as a characteristic which has its
adaptations like other characteristics, it has one peculiarity--its increase is
always opposed by lethal selection. The chances of life are reduced by
reproducing, inasmuch as more danger is entailed by the extra activities of
courtship, and later, in bearing and caring for the young, since these duties
reduce the normal wariness of individual life. The reproductive rate,
therefore, always remains at the lowest point which will suffice for the
reproductive needs of the species. For this reason alone the non-sustentative
form of selection might be expected to be the predominant kind.
J. T. Gulick and
Karl Pearson have pointed out that there is a normal conflict between natural
selection and fecundal selection. Fecundal selection is said by them to be
constantly tending to increase the reproductive rate, because fecundity is
partly a matter of heredity, and the fecund parents leave more offspring with
the same characteristic.
Lethal
selection, on the contrary, constantly asserts its power to
!reduce the
reproductive rate, because the reproductive demands on the parents reduce their
chances of life by interference with their natural ability of self-protection.
This is quite true, but the analysis is incomplete, for an increased number of
progeny not only decreases the life chances of the parents, but also of the
young, by reducing the amount of care they receive.
In short, lethal
selection and reproductive selection accomplish the same end--a change in the
constitution of the species--by different means; but they are so closely linked
together and balanced that any change in the operation of one is likely to
cause a change in the operation of the other. This will be clearer when the
effect of reproductive selection is studied in man.
!
Recalling the
truism that most human characters have a hereditary basis,
it is evident
that the constitution of society will remain stable from generation to
generation, only if each section of society is reproducing at the same rate as
every other (and assuming, for the moment, that the death-rate remains
constant). Then if the birth-rate of one part of the population is altered, if
it is decreased, for example, the next generation will contain proportionately
fewer representatives of this class, the succeeding generation fewer still, and
so on
indefinitely--unless
a selective death-rate is operating at the same time. It is well known not only
that the death-rate varies widely in different parts of the population, as was
pointed out in the earlier part of this chapter, but that the birth-rate is
rarely the same in any two sections of the population. Evidently, therefore,
the make-up of
society must
necessarily be changing from generation to generation. It will be the object of
the rest of this chapter to investigate the ways
!in which it is
changing, while in the latter half of the book we shall point out some of the
ways in which it might be changed to better advantage than it is at present.
Sexual
selection, or differential success in marrying, will be discussed
at some length
in Chapter XI; here it may be pointed out that the number who fail to marry is
very much greater than one often realizes. It has already been noted that a
large part of the population dies before it reaches the age of marriage. Of
1,000 babies born in the United States, only 750 will reach the average age of
marriage; in some countries half
of the thousand
will have fallen by that time. These dead certainly will leave no descendants;
but even of the survivors, part will fail to marry. The returns of the
thirteenth U. S. census showed that of the males 45-64 years of age, 10% were
single, while 11% of the females, 35-44 years old, were single. Few marriages
will take place after those ages. Add the number who died unmarried previous to
those ages, but after the age of 20, and it is safe to say that at least
one-third of
!the persons
born in the United States die (early or late) without having married.
The
consideration of those who died before the age of marriage properly comes under
the head of lethal selection, but if attention is confined
to those who,
though reaching the age of marriage, fail to marry, sexual selection still has
importance. For instance, it is generally known (and some statistical proof
will be given in Chapter XI) that beauty is directly associated with the chance
of marriage. The pretty girls in general marry earlier as well in larger
percentage; many of the ugly ones will never find mates. Herbert Spencer argued
ingeniously that
beauty is
associated with general mental and healthy superiority, and the more exact
studies of recent years have tended to confirm his generalisation. A recent,
but not conclusive, investigation[65] showed beauty to be correlated with
intelligence to the extent of .34. If this
is confirmed, it
offers a good illustration of the action of sexual selection in furthering the
progressive evolution of the race. Miss Gilmore, studying a group of normal
school graduates, found a direct correlation between intelligence (as judged by
class marks) and early
!marriage after
graduation. Anyone who would take the trouble could easily investigate numerous
cases of this sort, which would show the effect of sexual selection in
perpetuating desirable qualities.
!Fecundal
selection, then, is becoming the important phase of reproductive selection, in
the evolution of civilised races. The differential birth-rate is, as we have
often insisted, the all-important factor of eugenics, and it merits careful
consideration from all sides.
Such
consideration is made difficult by the inadequate vital statistics
of the United
States; but there is no doubt that the birth-rate as a whole is low, as
compared with that of other countries; although as a whole it is not
dangerously low and there is, of course, no necessary evil in a low
!birth-rate, of
itself, if the quality be satisfactory. The U. S. Census tabulation for 1915
gives the following comparison of the number of babies born alive each year,
per 1,000 population, in various countries:
Russia in Europe
(1909) 44.0
Japan (1911) 34.1
Italy (1913) 31.7
Austria (1912) 31.3
Spain (1913) 30.4
Austria (1913) 28.3
German Empire
(1912) 28.3
Holland (1913) 28.1
Denmark (1913) 25.6
Norway (1913) 25.3
United States
(registration area only, 1915) 24.9
England and
Wales (1913) 24.1
Sweden (1912) 23.8
Switzerland (1913) 23.1
Belgium (1912) 22.6
!France (1912) 19.0
The United
States birth-rate may, on its face, appear high enough; but its face does not
show that this height is due largely to the fecundity
!of immigrant
women. Statistics to prove this are given in Chapter XIII, but may be
supplemented here by some figures from Pittsburgh.
Ward 7, in that
city, contains the homes of many well-to-do, and contains more representatives
of the old American stock than any other ward in the city, having 56.4% of
residents who are native born of native parents while the majority of the
residents in nearly all the
!other wards in
the city are either themselves foreign-born, or the offspring of foreign-born
parents.
!Ward 7 has the
lowest birth-rate and the lowest rate of net increase of any ward in the city.
With this may be
contrasted the sixth ward, which runs along the south bank of the Allegheny
river. It is one of the great factory districts of
the city, but
also contains a large number of homes. Nearly 3,000 of its
!14,817 males of
voting age are illiterate. Its death-rate is the highest in the city. Almost
nine-tenths of its residents are either foreigners or the children of
foreigners. Its birth-rate is three times that of the seventh ward.
Taking into
account all the wards of the city, it is found that the birth-rate rises as one
considers the wards which are marked by a
large foreign
population, illiteracy, poverty and a high death-rate. On the other hand, the
birth-rate falls as one passes to the wards that
have most
native-born residents, most education, most prosperity--and, to some extent,
education and prosperity denote efficiency and eugenic value. For 27 wards
there is a high negative correlation (-.673),
!between birth-rate
and percentage of native-born of native parents in the population. The
correlation between illiteracy and net increase[66] is +.731.
!The net
increase of Pittsburgh's population, therefore, is greatest where the
percentage of foreign-born and of illiterates is greatest.
The significance
of such figures in natural selection must be evident. Pittsburgh, like probably
all large cities in civilised countries,
!breeds from the
bottom. The lower a class is in the scale of intelligence, the greater is its
reproductive contribution. Recalling that intelligence is inherited, that like
begets like in this respect, one can hardly feel encouraged over the quality of
the population of Pittsburgh, a few generations hence.
Evidently, there
is no difficulty about seeing this form of natural selection at work, and at
work in such a way as greatly to change the character of one section of the
species. For comparison, some figures
are presented
from European sources. In the French war budget of 1911 it appears that from
1,000 women between the ages of 15 and 50, in different districts of Paris, the
number of yearly births was as
!follows:
Very poor 108
Poor 99
Well-to-do 72
Very prosperous 65
Rich 53
!Very rich 35
!Disregarding
the last class altogether, it is yet evident that while the mother in a wealthy
home bears two children, the mother in the slums bears four. It is evident then
that in Paris at the present time reproductive selection is changing the mental
and moral composition of the population at a rapid rate, which can not be very
materially reduced even if it is found that the death-rate in the poorer
districts is considerably greater than it is on the more fashionable
boulevards.
J. Bertillon has
brought together[67] in a similar way data from a number of cities, showing the
following birth-rates:
!
!
Obviously, in
all these cases reproductive selection will soon bring
about such a
change in the character of the population, that a much larger part of it than
at present will have the hereditary
!characteristics
of the poorer classes and a much smaller part of it than at present the
hereditary characteristics of the well-to-do classes.
David Heron and
others have recently studied[68] the relation which the birth-rate in different
boroughs of London bears to their social and economic conditions. Using the
correlation method, they found "that in London the birth-rate per 1,000
married women, aged 15 to 54, is highest where the conditions show the greatest
poverty--namely, in quarters where pawnbrokers abound, where unskilled labor is
the
principal source
of income, where consumption is most common and most deadly, where pauperism is
most rife, and, finally, where the greatest proportion of the children born die
in infancy. The correlation
coefficients
show that the association of these evil conditions with the relative number of
children born is a very close one; and if the question is put in another way,
and the calculations are based on
!measures of
prosperity instead of on measures of poverty, a high degree of correlation is
found between prosperity and a low birth-rate.
Fortunately, it
is very probable that the differential birth-rate is not of such ominous import
in rural districts as it is in cities, although some of the tribes of
degenerates which live in the country show birth-rates of four to six children
per wife.[70] But in the more highly civilized nations now, something like a
half of the population lives in urban districts, and the startling extent to
which these urban
!populations
breed from the bottom involves a disastrous change in the balance of population
within a few generations, unless it is in some way checked.
Just how great
the change may be, statistically, has been emphasised by Karl Pearson, who
points out that "50% of the married population provide 75% of the next
generation," owing to the number of deaths before maturity, the number of
celibates and the number of childless
!marriages.
"The same rule may be expressed in another way: 50% of the next generation
is produced by 25% of the married population." At this rate in a few
generations the less efficient and socially valuable, with their large
families, will overwhelm the more efficient and socially valuable, and their
small families.
Fecundal
selection is at work to-day on a large scale, changing the character of the
population, and from a eugenic point of view changing it for the worse.
Fortunately, it is not impossible to arrest this
!change.
But, it may be
objected, is not this change merely "the survival of the fittest?" In
a sense, yes; and it is necessary that the more intelligent classes should make
themselves "fitter" to survive, by a change of attitude toward
reproduction. But the dying-out of the intellectually superior part of the
population is a pathological condition, not a part of normal evolution; for
barring artificial interference with the
!birth-rate,
fertility has been found to go hand in hand with general superiority. This
demonstration is due to F. A. Woods' study[71] of 608 members of the royal
families of Europe, among whom, for reasons of state, large families are
desired, and among whom there has probably been little restraint on the
birth-rate. Averaging the ratings of his individuals from grade 1, the mentally
and physically very inferior, to grade 10, the mentally and physically very
superior, he found that the number of children produced and brought to maturity
increased in a fairly direct ratio.
Investigations
of Karl Pearson and Alexander Graham Bell[72] show that fecundity and longevity
are associated. It follows that the mentally
and morally
superior, who are the most fecund, are also the longest-lived; and as this
longevity is largely due to inheritance it
!follows that,
under natural conditions, the standard of the stratum of society under
consideration would gradually rise, in respect to longevity, in each
generation.
Such is probably
one of the methods by which the human race has gradually increased its level of
desirable characters in each generation. The desirable characters were associated
with each other, and also with fecundity. The desirable characters are still
associated with each other, but their association with fecundity is now
negative.
It is in this
change that eugenics finds justification for its existence as a propaganda. Its
object is to restore the positive correlation
!between
desirable characters and fecundity, on which the progressive evolution of the
race depends.
!The bearing of
natural selection on the present-day evolution of the human race must be
reviewed in a few closing paragraphs.
Selection by
death may result either from inadequate food supply, or from some other lethal
factor. The former type, although something of a bugaboo ever since the time of
Malthus, has in reality relatively little effect on the human race at present.
Non-sustentative lethal selection
!in man is
operating chiefly through zymotic diseases and the bad hygiene of the mentally
inferior.
Reproductive
selection is increasingly effective and its action is such as to cause grave
alarm both through the failure of some to marry properly (sexual selection) and
the failure of some to bear enough
children, while
others bear too many (fecundal selection). It is obvious that the racial result
of this process will depend on what kind of people bear and rear the most
children; and it has been shown that in general the larger families are in the
section of the population that
!makes fewer
contributions to human prosperity and happiness, while those endowed with great
gifts, who ought to be transmitting them to their children, are in many cases
not even reproducing their own number.
!Natural selection raised man from ape-hood to
his present estate. It is still operating on him on a large scale, in several
ways, but in none of these ways is it now doing much actually to improve the
race, and in some ways, owing to man's own interference, it is rapidly
hastening race degeneracy.
CALEB SALEEBY’S Parenthood & Race Culture: An Outline of Family Eugenics
