"...in not too many generations differential fertility could swamp the
effects of anything else we may do about our economic standing in the


IQ and falling birthrates
R.J. Herrnstein
The Atlantic, May 1989 v263 n5 p72(7)

Bright, well-educated American women of all races are having fewer children,
a phenomenon the author believes may affect national productivity and the
gene pool


concern frequently from young men and women passing through Harvard-more
than ever before in my three and a half decades here. And I hear about it in
conversations with my peers, frustrated by the slow accumulation of
grandchildren. This concern is at least mildly ironic, coming, as it does,
two decades after alarms about a "population explosion."

Though populations in South America and Africa and the Indian subcontinent
continue to grow at an alarming rate, the U.S. media direct their attention
increasingly to labor shortages in industrial societies and to shrinking
school populations in affluent American suburbs. Thinking people have heard,
and are talking, about the "birth dearth," as Ben Wattenberg named it in the
title of a recent book. Day-care and parental benefits, which will
presumably increase the birth rate, earn approving mention in the platforms
of both political parties and in glossy annual reports of large companies.

The concern about fertility also bubbles to the surface in artistic
renderings of contemporary and future life-in light movies like Baby Boom
and Three Men and a Baby, for example, about young women or men trying to
reconcile careers and parenthood, and in serious novels, like Margaret
Atwood's Handmaid's Tale, with its fantasy of a not-too-distant future in
which the dwindling number of fertile women are made slaves to procreation.

Low fertility, of course, is hardly a new worry. Some of its history,
especially that in Europe since the middle of the nineteenth century, is
well and compactly told by Michael Teitelbaum and Jay Winter in their book
The Fear of Population Decline. Some French writers attributed the defeat of
their nation in the Franco-Prussian War, in 1871, to the slow French rate of
reproduction, as compared with that of fecund Germany. Fertility became a
central issue in early-twentieth-century French politics. Besides being
blamed for France's inability to field an army large enough to defeat the
Germans and also have a functioning economy at home, low fertility was seen
by various contemporary French commentators as the cause or the effect of
"national degeneracy," a disease of the French spirit.

Fiction echoed reality, as it does everywhere. In Emile Zola's novel
Fecondite, written at the turn of the century, happiness and personal
triumph came to a working-class couple with fifteen children and scores of
grandchildren, rather than to various unappealing bourgeois, with their
selfishly hedonistic but ultimately miserable lives, their Malthusian
rhetoric bemoaning fecundity, and, above all, their small families. Zola was
one of the founding members of the National Alliance for the Growth of the
French Population.

In Great Britain, too, arguments about reproduction were part of the
political landscape before and after the turn of the century. As in France,
a disastrous and costly war heightened public alarm. But the British had
been outfought in southern Africa, rather than outnumbered, by the Boers,
even though the British eventually won the war. Considerations of the losses
of the Boer War emphasized not so much the question of how many British
soldiers but of how good they were. If the French worry about fertility was
characterized as mainly quantitative, the British worry was mainly

The worries went beyond the quantity and quality of armies. Teitelbaum and
Winter describe a British preoccupation with the general "physical deteriora
tion" of the population; with what was called the residuum, meaning urban
unskilled workers; and with the "proliferation of the unfit" versus the
underreproduction of the fit. Prime Minister Arthur Balfour worried publicly
in 1905 that the very members of the working class who showed the enterprise
and ability to improve their lot were the ones who limited their own
fertility, while those who did not get ahead bred beyond their capacity for
taking good care of their children. "Everything done towards opening up
careers to the lower classes did something towards the degeneration of the
race," he said.

In our time, Prime Minister Lee Kuan Yew, of Singapore, has said, "Levels of
competence will decline, our economy will falter, our administration will
suffer, and society will decline" because so many educated men are failing
to find educated women to marry and are instead marrying uneducated women or
remaining unmarried. But Lee is an exception, for few modern political
leaders dare to talk in public about the qualitative aspect of low
fertility. We know why this is, and it has less to do with whether or not we
have a fertility problem than with the unacceptability of talking about the
subject. In our century the Nazis made selective fertility an emblem of
National Socialism, with malevolent consequences that need no review here.
Hence even to mention fertility in relation to nation or race has become

Nonetheless, human fertility, particularly in its qualitative aspect, has a
special and direct relation to economic productivity. A full study of
fertility and productivity would, of course, cross many frontiers of
scholarship, but my focus is narrower. My subject is differences among
groups within the population: how these differences affect fertility and how
that, in the long run, may affect the society's economic well-being. Partly
because of our ghastly memories of the Nazis, many social theorists and
scientists have for some time been reluctant to take such differences into
account. Society, these social scientists say, must be studied at the level
of broad social forces, not at the level of small subpopulations. But
however useful and illuminating the abstractions of social theory are, the
actual life of a society must consist of myriad individual human actions. In
the present instance the social consequences of reproduction are illuminated
by the study of individual differences, and the light it sheds spreads
further than many realize.


rates, the difference between the two rates determining the direction and
size of population growth (if we set aside complications like migration and
age at reproduction). With the advent of industrialization, mortality rates
fall. Since birth rates remain high, the first consequence of
industrialization is a rise in population. This is what alarmed Thomas
Malthus, who wrote at the end of the eighteenth century to warn of the
tendency of populations to expand to the point of marginal subsistence.

Malthus could not have known that in the next stage of this process of
demographic transition, as it is known among demographers, the birth rate
falls, largely or totally compensating for the fall in mortality rates. The
average number of live births per American woman, for example, fell from
about eight in the 1700s to about two in the 1970s. The timing and size of
the two components of the demographic transition-the fall in death rates and
the fall in birth rates-may vary from nation to nation, but the transition
itself is as close to a demographic universal as social science has

This purely quantitative aspect of the transition is quite well known,
unlike the qualitative aspect, which may in the long run be no less
significant socially. Robert Retherford, of the East-West Population
Institute, in Honolulu, has examined dozens of empirical studies, from many
countries, of the demographic transition in relation to social status. The
evidence shows that prior to the transition women of high status had higher
fertility than those of low status. Among the possible reasons for this:
high-status women usually enjoyed better health, they married earlier,
because their spouses could afford to start families earlier in life, and
they endured fewer and shorter separations from their spouses than
low-status women did.

After the transition the overall birth rate is lower, but now women of high
status usually have lower fertility than those of low status. Health and
marital separation cease to be major factors in fertility, and because of
the educational opportunities open to women of high status or high
intelligence, their age at marriage rises above that for women who, for
whatever reason, lack those opportunities. More-subtle changes, involving
the social relation between men and women, may further depress fertility,
especially at the upper end of the social and intellectual range.

With only rare exceptions, according to the evidence that Retherford has
assembled, the fall in fertility during the transition is thus not just a
fall but also a redistribution. At first glance the demographic transition
seems biologically perverse. Why do people limit their fertility just when
improved conditions of life-as reflected in the reduced mortality rate-might
allow them to raise more children successfully? And why should more
limitation of fertility take place at high social-status levels than at low?
Theorists have several hypotheses.

Economic theorists have noted a simple economic fact about
industrialization, one that may influence people's decisions about family
size. Economic resources flow from children to parents before
industrialization, and vice versa afterward. Another pair of hands on the
farm is transformed, after the demographic transition, into another mouth to
feed or another tuition to pay. Industrialization and modernization may tip
the economic balance toward small families, and do so at higher
social-status levels more than at lower, if people calculate consequences at
 all rationally, as economists usually assume they do.

Theorists with a more biological orientation have suggested that after
industrialization people may focus more on the quality of offspring than on
the quantity. A few well-nurtured children may have been, at some point in
our evolutionary history, a better long-term strategy for the survival of
parental genes than many children at the brink of extinction. This means
that those who have fewer children may, theoretically, have more
grandchildren who reach reproductive age. Biologists theorize that from the
evolutionary pressures of such an era, if it existed, we may have inherited
behavioral dispositions that favor lower birth rates as conditions improve
on the average-as they do in the transition to an industrialized society for
those who succeed in that society. Whether or not the reduced birth rate
after industrialization is justified rationally is beside the point as far
as this theory is concerned, for the inherited traits of an era arise from
the selective processes of an earlier era.

Another biological approach to the demographic transition looks at the
differing pressures of parenthood on women and men. Females and males
inevitably have different investments in offspring. Mothering is more
depleting than fathering. For example, the number of ova per woman is quite
limited, compared with the virtually unlimited number of sperm per man. A
woman can have little more than one pregnancy a year; a man has no such
limitation on his reproductive rate. Each of a woman's children represents a
greater fraction of her reproductive potential than does each of a man's.
Because she invests more in each child, she is more vulnerable biologically,
and perhaps psychologically, to anything that threatens an offspring.
Because of this special vulnerability, the customary sexual division of
labor-whether or not its origins are inherited-places on mothers a
disproportionate share of the burdens of child-rearing.

One difference between human beings and their close biological relatives is
that human intelligence has made salient the different stakes that women and
men have in parenthood. As human intelligence evolved, women came to
understand more clearly than their simian ancestors the risks, pains, and
obligations of motherhood, and how these contrasted with the consequences of
fatherhood. Women should therefore have come to prefer smaller numbers of
children, and they have. They may want the first child or two as much as or
more than their spouses do, but in the aggregate women in most societies who
express a preference for a particular family size prefer small families, and
in few societies do they prefer large ones. Further, women who express a
preference-suggesting that they feel they have a say in family size-tend to
have fewer children than those who, fatalistically, do not express any
preference at all.

No species can survive in the long run, however, if its female fertility
falls below what demographers call the replacement rate: the number of
children an average woman must have in order to maintain a constant number
of women from generation to generation. Since our species continues to
flourish, the tendency toward childlessness must, therefore, have been
counteracted by evolution and by culture, during the hundreds of thousands
of years since the dawning of human intelligence.

One theory defended by a number of contemporary researchers holds that birth
rates drop when a society modernizes if one of the corollary effects is to
free women to any extent from the cultural pressures forcing them toward
motherhood or keeping them subservient to men. If, for example, they become
less dependent on or less threatened by men, and more free to choose a style
of life, they will, if the theory is right, choose fewer children. They can
just say no.

Inexpensive contraception should hasten the decrease in fertility as women
are liberated, by separating the rewards of sexual activity from the costs
of parenthood. Contemporary women may choose sex and reject motherhood, an
option unavailable to women sexually oppressed and without access to birth
control. The calls for the right to abortion come largely from these
contemporary women. This theory implies a differential fall in fertility
within a society. The number of offspring may decrease most among
more-intelligent women, since they are most aware of the costs of
motherhood, all of which are deferred from the moment of fertilization. Sex
comes first, the pains and costs of pregnancy and motherhood later. Much
research suggests that the less intelligent people are, the less they are
likely, on the average, to be influenced by the delayed consequences of
their behavior. Women from the higher social strata-and more-intelligent
women-are also likely to have fewer children because they are more likely to
find rewarding occupations other than, and competing with, motherhood.
Societies that manage to keep women subjugated while industrializing should,
according to this theory, avoid or reduce the qualitative effect of the
demographic transition. Their women-especially their advantaged women-should
have more children relative to the historical norms of their society than
comparable women in other industrialized societies.

While all these theories about the failing birth rates of the demographic
transition are probably right to some extent, the exceptions to the general
pattern are well explained by taking sex-role differences into account. The
relevance of women's rights to the demographic transition is exemplified by
the experience of Japan. Daniel Vining, a demographer, has summarized the
evidence showing that educated, upper-class Japanese women did not bear
fewer children than women lower on the social ladder as their country grew
industrially after the Second World War, and they also did not enjoy as much
cultural and economic liberation as did women in modern societies elsewhere.
Japan seems to have passed through the quantitative aspect of the transition
without experiencing much of the qualitative, reducing fertility rates more
or less uniformly all along the social scale. In the Muslim nations as well,
childbearing has not shifted disproportionately to women of lower strata,
and in that culture, too, women have by Western standards remained

WE MIGHT BE CONCERNED ABOUT THE REDISTRIBUtion of childbearing toward lower
social strata for many reasons, among them the correlation between social
status and socially important traits. Intelligence, as measured by
intelligence tests, is one such trait. Because parents and children tend to
have comparable levels of measurable intelligence, the average intelligence
of the population will decline across generations to the extent that
reproduction shifts toward the lower end of the scale (assuming no other
influence on the average level). This decline does not depend only on the
genetic factor in intelligence, even though most contemporary researchers
say that the genetic factor is large. Differential reproduction shifts a
population toward the characteristics of the more prolific parents for all
traits in which parents and children resemble each other, for whatever

Are brighter women, in fact, having fewer children than less bright women in
the United States? Except for the time of the (atypical) Baby Boom,
fertility and tested intelligence have been negatively related in several
national samples of Americans. The best, albeit still tentative, estimates
imply about a one-point drop per generation over the population as a whole,
other things being equal. The decline would be larger in the black
population than in the white, because black women show a steeper fertility
differential in relation to IQ. Using historical estimates of overall
American birth rates, Vining tentatively infers the equivalent of a
four-to-five-point drop in IQ over the five or six generations spanning the
demographic transition in the United States, with only the Baby Boom
generation's IQ not dropping. This may not seem like much, but the drop is
large if we consider the "tails" of the distribution of intelligence and not
just its average. For example, a five-point drop in the average, if the
distribution of scores has the "normal" (that is, the familiar bell-curve)
shape, would result in almost a 60 percent reduction in the fraction of the
population with IQ scores over 130 and a comparable increase in the fraction
with IQ scores below 70. It may be the tails of the distribution, more than
the average, that we should be worrying about.

The Japanese population has a higher average IQ than the American. In public
discussion this IQ differential is usually attributed to the superiority of
Japanese schools, but the difference is already present in the earliest
years of primary school, and has grown in recent generations. The superior
IQ scores of the Japanese population may be to some extent yet another
consequence of the demographic transition, which, as noted above, has had
less of a differential effect within Japan than it has had here.


AN IQ POINT OR TWO ON THE AVERAGE SEEMS A SMALL price to pay for the other
consequences of modernization, especially the liberation of women. So why
should we care if the intelligence of our population is shifting downward?
Can we not compensate in our schools for whatever small cost we are paying
in lost intellectual ability? That is certainly a possibility, but most
people who express that hopeful notion underestimate the cost we pay,
economically and perhaps otherwise as well, for lost IQ points.

As a rule of thumb, more-educated people in a modern society are more
intelligent, as measured by standard tests, and vice versa-chiefly because
societies usually invest educational resources in the people who make the
best use of them, and that usually means the people with the high scores.
Whether or not one approves of it, education and intelligence are thus
correlated-but they are not identical. They can be pulled apart, at least a
bit, as a matter of public policy. During the Cultural Revolution in China a
centuries-old Chinese tradition of educational selection by objective tests
was for a time abandoned. Closer to home, judges and legislatures in this
country have been regulating or banning the use of objective tests for
school placement and university admissions.

Occupational success in modern societies is linked to education. For decades
study after study has shown that people who do well in school are more
likely also to do well socioeconomically. Therefore, one line of reasoning
goes, the key to productivity and individual achievement is education-rather
than individual traits that predict educational success.

If that reasoning were sound, we would be in increasingly excellent shape,
compared with the rest of the world. The United States has decisively left
the competition behind in sending its population to school. From 1900 to the
present the proportion of the American population completing high school
rose from 10 percent to over 70 percent. In the 1970s about half of all high
school graduates went to college. In the Soviet Union, in contrast, about 10
percent of all high school graduates (who are a smaller fraction of the
population to begin with than are graduates in the United States) went on to
the next level of education. Western European countries and Japan also fall
short of the American standard, graduating fewer than 70 percent (in Italy,
the Netherlands, and West Germany the number is fewer than 20 percent) of
their high school students, and admitting far fewer of those graduates to
college. Similarly, American schoolteachers have, on the average, more years
of post-secondary education than teachers anywhere else.

Sending more people to school has no doubt produced benefits in the quality
of American life, but instead of an educated populace, we find widespread
illiteracy and its mathematical equivalent, innumeracy. Many Americans are
going to school more but, apparently, learning less. Schools are being
criticized for their lack of rigor, for failing to instill a love of
learning; society as a whole is criticized for underpaying and
underappreciating teachers. These criticisms may in time lead to
improvement. For the present, however, the fact is that the expansion of
schooling has not done the job we expected it to do, and its disappointments
are evident not just in the classroom. While America has been sending more
people to school, it has also been losing ground in the growth of worker
productivity, compared with nations having less-schooled populations, such
as Japan and West Germany. We now know, to our regret, that something more
fundamental than schooling per se explains the historical role of education
as a ladder to economic success.

Thanks to a remarkable series of studies by applied psychologists,
especially John Hunter, Frank Schmidt, and their associates, we know quite a
lot about the predictors of individual occupational success in the United
States. Overturning the conventional wisdom of several generations of
experts, their analyses prove that variations in intelligence, as measured
by IQ and IQ-like tests (such as the U.S. Employment Service's General
Abilities Test Battery), predict job productivity to an extraordinary

Because job performance is correlated with intelligence, we now know not
only that the productivity of the American work force as a whole, and within
particular occupations in given locations, can be improved by the use of
intelligence tests for job placement, but also how much improvement is
possible. For example, one analysis estimated that Philadelphia would lose
$170 million in productivity over a ten-year period by not using an
intelligence test when hiring recruits for the police department. Losses
that are larger per person hired would be incurred by failing to test
applicants for jobs demanding greater cognitive complexity, such as computer
programming. For the American work force as a whole, after taking into
account the number of people at all levels of intelligence, the productivity
differential between a labor force selected by intelligence tests and one
selected at random from applicant pools was estimated to be worth a minimum
of $80 billion in 1980-about the size of the total annual corporate profit
for the Fortune 500 in that year.

When these new analytic methods are applied to thousands of separate studies
of worker performance in relation to intelligence, certain broad
generalizations follow. Intelligence tests predict performance (as measured
by on-the-job trainability, objective measures of job proficiency, or
supervisor ratings) in hundreds of common occupations. Performance in a job
requiring greater cognitive complexity, such as the job of manager, is more
strongly associated with intelligence than performance in one requiring
less, such as that of sales clerk. But even for a job at the lowest level of
cognitive complexity, such as off-loading conveyor belts, intelligence has
predictive power.

The predictive validity of intelligence-test scores, expressed as a
correlation coefficient between the score and some measure of job
performance, seems to vary from about 0.2 to about 0.6 for individual
occupations, and to average about 0.5 for the work force as a whole. If this
finding holds up, it is an astonishing result. It says that on the average
about 25 percent of the variation in worker productivity can be accounted
for by the scores on intelligence tests that can be administered in an hour
or so.

Performance in occupations demanding little cognitive complexity is usually
best predicted by scores on tests of psychomotor skills (eye-hand
coordination, simple reaction time, and so forth), rather than on tests of
intellectual ability. Therefore the use, for hiring and promotion, of some
combination of intelligence and psychomotor scores, suitably weighted for
particular occupations, would predict job productivity even better than the
use of either or, obviously, the use of neither, which seems to be a fond
hope of advocates of various causes.

One study compared intelligence-test scores with ten other plausible
predictors of productivity (job tryout, biographical inventory, reference
check, experience, interview, training and experience ratings, academic
achievement, education, interest, and age) of entry-level employees in a
variety of occupations. All the variables except age had some predictive
validity, but intelligence scores, with a validity coefficient of 0.53, had
the most. Near the bottom, with coefficients of 0.11 and 0.10, were academic
achievement and education, respectively. For employees already on a job,
intelligence scores predicted performance after promotion as well as, or
better than, measures based on past performance.

Educational level may be a better predictor than intelligence of
occupational attainment in the United States, as many studies have shown,
but for occupational performance, intelligence is the better predictor by
far. Employers may use educational credentials to hire or promote their
employees because they do not understand the power of, do not have
available, or are simply reluctant to use measures of intelligence. But the
failure to use intelligence measures seems costly in terms of productivity.
The evidence also shows that the distribution of intelligence matters in its
own right, and not just in relation to the effect of intelligence on success
in school.

sending more people to school for more years seems to offer little benefit
to economic performance, although doing so may be worthwhile for other
reasons. At one time schooling was largely reserved for socioeconomically
privileged people. Opening the schools to the rest of the population
harvested a vast benefit, intellectually and economically, but we seem to
have passed the point at which a large economic gain can be made by merely
increasing access to schooling.

The data suggest, however, that schools could be improved so as to develop
the very intellectual skills that are so predictive of productivity, and
perhaps to further other social purposes. Even the most confirmed believer
in the genetic factor in intelligence knows that the environment contributes
significantly. Most such believers would probably also agree that schools
can play a major role in developing intelligence. For schools to do so would
take new knowledge about cognitive development and a redirection of how they
go about their business. What is needed, in short, is more support for
research on intellectual variation and development, and less political
restraint on engaging in it and then applying its findings.

Second, we should be conscious of how public policy interacts not just with
education but also with other influences on the intellectual quality of the
population, such as the differential in the fertility rates of women of
different intelligence. Many things may be done short of the horrors of The
Handmaid's Tale. Nothing is more private than the decision to bear children,
yet society has a vital interest in the aggregate effects of those
decisions. This issue demands informed public consideration, and probably
also public action to lessen the tension between parenthood and career. At
the very least, we should stop telling bright young women that they make
poor use of their lives by bearing and raising children, as commencement
speakers and others have implied to educated women for decades.

The competing ideals of equality and efficiency create a dilemma of long
standing. For various reasons, the dilemma is keenly felt in America. The
goal of efficient production competes with the goal of a more equal
distribution of wealth. We can, we believe, gain greater equality with
little or no cost in productive efficiency, especially by investing more in
education. But the data now tell us that economic efficiency depends on
still intractable individual characteristics, given current methods of
education. The individual characteristics run in families for reasons not
easily overridden by social policy. Whatever else we may want to infer from
that fact, we ought to bear in mind that in not too many generations
differential fertility could swamp the effects of anything else we may do
about our economic standing in the world.

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