Human Population: What Are the Limits?
A Conversation with Paul Demeny
From the Environmental Review Newsletter Volume Two Number Eleven, November 1995
Introduction:
The world population is now approximately 5.7 billion people, most of whom live in developing countries.
It is thought that as the developing world becomes more industrialized and urban, that people will have fewer
children, and the world population should peak around 12 billion early in the next century. The reduction in birth
rate due to the shift from an agrarian to an urban, industrial/service economy, occurred first in Europe, then
North America and Japan, and most recently in East Asia; that is, the process seems to be independent of culture
and geography.
We spoke with Professor Paul Demeny of the Population Council, a private research and technical
assistance organization based in New York. Dr. Demeny came to the U.S. from Hungary in 1956, received the
Ph.D. in economics from Princeton University in 1961. He became a full professor in 1969 at the University of
Michigan and established the Institute on Asia and Pacific Matters at the East West Institute at the University of
Hawaii in 1971. He was vice president and director of the Center for Policy Studies at the Population Council
until 1988, and is now a distinguished scholar there.
Professor Demeny established the quarterly journal, Population and Development Review, in 1974. The
journal seeks to advance knowledge of the relationships between population and socioeconomic development and
provides a forum for discussion of related issues of public policy. Subscriptions cost $32.00 for one year. The
journal can be reached at Population and Development Review, One Dag Hammarskjöld Plaza, New York, New
York 10017. Phone (212)339-0514
ER: Dr. Demeny, what is the purpose of the Population Council?
PD: The Council's purpose is a better understanding of world population growth and its processes, and a better
understanding how such knowledge can be turned to the betterment of humankind.
The Council has three broad divisions: One does social science research, one does biomedical research, and
one is specializing in technical assistance matters, advising governments and organizations primarily in the Third
World about population matters. My own field is the economic aspects of population change, combining
demography and economics.
ER: How many people are there in the world now?
PD: Currently 5.7 billion. Of course, very finely specified figures ought to be taken with a big grain of salt
because there is still an element of uncertainty in the estimates. It would be fair to state the total world
population, at 5.7 billion plus or minus 100 million.
A good deal of what we know about the population comes from sample surveys and from fragmentary and
sometimes quite deficient data.
ER: How good are the population estimates for some of the less developed countries like Bangladesh?
PD: For the population size, there is an error term around the total figure, but the magnitude is certainly right. Now if you ask, what about the birth rate, we are getting a little more uncertain. And if you are asking, how
does this birth rate compare to the birth rate five years ago, we have an even trickier question. Because when
you go into depth about how many maternal deaths there are, that would require very fine vital registration
systems that do not exist. So in that case, the estimates get larger and larger error terms.
ER: Why has the world population gotten so high so fast?
PD: One has to keep in mind that although there was remarkable acceleration of the rate of population growth
starting after the Second World War, the acceleration of growth can be traced back at least till 1700 or 1650.
And it has been accelerating quite steadily all the way into the mid or late 1960s. And the short answer why this
has happened is control of mortality; namely, improvement of health conditions, better housing, somewhat better
nutrition, and at a later stage, better public health measures and medical care. I am describing primarily the
original accelerator of population; namely, the population of the West. When we come to the 20th century, and
particularly when we come to the very great acceleration of the growth of the population at the middle of the
century, there, the impact of medical technology, pharmacology, and general public health measures was much
larger than in the classical mortality transition case when improving standard of living was more significant.
This opening up the gap between the birth rate and the death rate - which is how the rate of growth is
defined - was primarily not because birth rates have been rising, but primarily because death rates have been
falling, and falling quite spectacularly and rapidly since the 1950s. However, there has been in many countries of
high fertility a temporary increase - not a major increase but a notable increase - also in the birth rates. So the
gap was widened also because of what happened to the birth rates.
ER: That would make the grwoth rate even higher.
PD: Yes. Globally, population growth rate peaked in the mid-1960s at about two percent per year. Two percent
per year does not sound like a big figure, but sustained two percent growth would double a population in thirty-five years, and that is a tremendously rapid population increase - historically unprecedented. The historical rate
of growth was way below this, even in the modern era, in the 19th century.
ER: What was the growth rate during the European expansion in the 19th century?
PD: In the 19th century, it was about one-half percent per year - an annual rate of growth of five for every
thousand people. As opposed to quadruple of that rate around 1965.
ER: What is the doubling time for a population growing at one-half percent per year?
PD: At one-half percent per year, the population would double in 140 years.
ER: So even a half percent growth doubles the population every four human generations.
PD: Indeed. Obviously, for any historically significant time period, such rates are simply unsustainable. There is
a classic way of showing this; namely, to assume that current rates of fertility and mortality are frozen and then
project the population into the future. If you do this, with the 1990 figures, by the middle of the 22nd century
you would get a world population of 680 billion. Now we know that this will not happen because it is
inconsistent with anything we know about economics and biology and the environment. So something has to
give. And the age-old remedy - a rise in the death rate - is not a pleasant remedy. So the only choice on the
global level, is a decline in the birth rate.
If you want to have long average length of life, you have to have also, very low fertility. For stability, you
would have to have an average family size of about two per couple for the simple reason that with low mortality
- what the advanced countries enjoy now - virtually every birth survives to a productive age.
People individually or collectively as societies, take stock and decide that an adjustment is needed, and
proceed to get the adjustment or persuade each other to have such an adjustment, so fertility declines. But this is
a process that takes time. So even if fertility would instantaneously drop to the replacement level of two, there
would be a period of quite substantial growth in most places in the world. This is the so-called momentum of the
population that would guarantee that population growth will continue from the present level well into the 21st
century.
ER: Can you explain the idea of population momentum?
PD: The birth rate is the number of births related to the total population. And even as the birth rate declines,
there are a disproportionately larger number of people who were born twenty-five years ago when fertility was
still very high. And even if they have a small number of children, their number is so high that the rate of births
will be high.
Also, a young population has a low death rate. So this gap between high birth rates and low death rates is
particularly acute with young populations - populations that in the recent past typically have had both high
mortality and high fertility. This is more pronounced in the developing world because there, fertility has been
quite a bit higher even than fertility at the peak of the baby boom in the United States.
ER: Why do we think world population will level off at around 11-12 billion people in the next century?
PD: One has to be always hesitant when one is prophesying about the future. Why fertility declined first in the
West and now quite spectacularly in the developing countries, particularly in East Asia but also at a number of
other places, we understand quite well.
In a nutshell, the social and economic changes that take place shift the calculation that every couple makes
in reproducing itself against the desire to have very large families. At the same time, technological change in
contraceptive methods also makes translation of the desire more easy and more readily available.
But the primary motive force is the shift from an agrarian to an industrial economy, from a rural to an
urban residence, from an economy where children are at an early age productive and useful to their parents, to
an economy where children become more costly and less economically useful and parents want fewer of them.
ER: The prospect of putting kids through college is certainly good birth control.
PD: Indeed. And also, rising expectations or rising standards of what is adequate are culturally and historically
determined matters, and they have been systematically changing against high fertility.
When you mentioned why will population stabilize far into the future, one answer is that because we expect
that these processes will be continuing and modernization will occur worldwide. And in addition, because
collectively societies will decide that they have to have a social contract that transmits social values and social
expectations to couples of what is the acceptable level of behavior.
And these expectations do get translated into policies that one hopes are adopted as a result of democratic
and constitutional processes. But in many cases, this is not even needed because the sound economic and social
development process is itself a very strong stimulus to create new patterns of demographic behavior with respect
to fertility.
Now, where does this point to, however, is a big unknown. And the usual and quite commonly accepted
notion that this demographic transition is headed towards population stabilization is a somewhat ill-supported
assumption.
The best demonstration of this is that in many advanced countries, spontaneous and voluntary fertility
limitation has brought fertility down to well below replacement levels. Now, forces may be generated that then
will eventually nudge the birth rates back to a higher level, enough to replace the population, but it is difficult to
specify what those forces precisely will be.
If larger families are totally eliminated voluntarily - as is the case in much of Western Europe now or in
Japan - then you have families consisting of two children or one child and typically a significant portion of the
female population remains childless. If you put these together, the average adds up to something considerably
less than two. So you have in a closed population - not counting international migration - the level of fertility
can be pointing towards population decline. And while this is the case in many of the western countries, in the
United States and in a few East Asian situations, we cannot be certain and cannot be making a very flat
statement how this will apply to Africa or South Asia forty years from now. They may follow this previous
model, or they may not.
I think, on balance, it is unlikely that a magic hand will calibrate fertility behavior so that it precisely yields
zero population growth. It may well be that by the middle of the 21st century, decline of population will set in
and an erosion of those very large numbers that this past fifty years and the next few decades will have built up,
which particularly in densely populated countries, may be precisely what the doctor has ordered and might be a
very welcome phenomenon.
But declining population does raise a number of relatively novel demographic and social questions,
primarily because of a pronounced population aging, and for matters of social security and the flexibility of the
labor force - even national defense - this can cause headaches.
ER: Do you assume that this assessment each couple makes, operates independently of culture and geography?
PD: As to whether the reactions or the calculation or the cultural patterns that produce the low birth rate in
Western countries will be applicable to, say, Africa, we have to be cautious because of the great cultural
differences. But we do know that what was once considered as a uniquely western pattern of demographic
behavior got very quickly established in the different cultural setting of Japan. And we also observe this in more
recent decades just about everywhere in Southeast Asia. And the process is now well advanced also in a good
part of South Asia; in particular, Southern India and in Bangladesh and in Sri Lanka.
So we have plenty of evidence that the forces that with modernization and with economic advance, depress
the birth rate work in a great variety of cultural settings. And it is unlikely that Africa would be an exception
from that rule. Certainly, in Latin America too, the pattern is very much with the time lag than was the pattern in
Europe earlier.
ER: Why are developing countries having their population boom a hundred years after Western Europe?
PD: Well, because of the slower rate of economic and social change - advancement, if you will - manifest in
such matters as the level of education. Until very recently, an overwhelming majority, certainly of women, in
South Asia were illiterate. As education spreads, as women's autonomy within the family and their economic
value rises, we find the same patterns developing that characterize earlier what happened in the West. For
instance, a higher level of education, a higher level of literacy, would be very likely inconsistent with the very
early age of marriage that characterized until recently a good deal of the developing world. That alone introduces
an element that depresses fertility and when women marry later - not at their middle teens but around twenty or
even beyond - they bring different mental equipment and a different bargaining power to family matters than
what was the case before.
And as industrialism spreads and urbanization spreads, what I referred to earlier as the shift towards more
expensive children and less economically useful children, more demanding standards of upbringing and
education, they have a force to make behavior change. When this is also helped by access to modern
contraceptive technology, the change can be spectacular or quite rapid. And we found that particularly in East
Asia: a transformation that took quite a long time in the West has been very greatly accelerated. Of course, these
birth rates typically started in the developing world to begin with, at a higher level than was the case in the
earlier European, history. But the transition from high to low fertility, has been getting speedier, partly
accelerated by governmental programs and governmental goading and determination to edge the birth rate down.
A classic example of this would be in Indonesia, where besides the forces of modernization, there was a very
systematic and determined government program that told couples - women in particular - that they are
expected to practice family planning and offer them at no charge, means of fertility control.
ER: The slogan that development is the best birth control came out of the Cairo population conference. I
question whether current models of economic development will cause a demographic transition to lower fertility
in some of the really poor developing countries.
PD: The slogan you referred to was actually hatched back in the first big intergovernmental population
conference in Bucharest. It so happened that the Indian minister of health who was representing India gave this
slogan and put it into current use. But in this last conference in Cairo, as was the case also before in Mexico
City, there was a good deal of emphasis on not relying on this quasi-automatic mechanism - that spontaneous
adjustment in response to development will reduce birth rate - but was asking also for concerted efforts to
provide access to contraceptive services to everybody who wants to have it.
The adjustment to lower birth rates is not magic if you have sound development, then those within family
calculations predictably do induce people to control their fertility. It would be very unlikely that Americans who
could easily feed six children, would decide to have six children. There are many more elements to the
calculation than just how many people can we feed.
What is more uncertain, however, is would declining fertility take place in a situation where economic
development is very slow and bumpy? One answer is that there is indeed more to the change than economic
calculation alone. People's expectations can change even if their immediate material surroundings are relatively
unchanged. And with modern methods of communication and exposure to the outside world, and radio and
television even to remote corners of the world, there are a good many factors that do work towards adjusting
individual behavior.
But perhaps even more significantly, there are then collective decisions concerning demographic change
such as family planning programs. And some of this tries to cater to existing latent demand for birth control,
people who would like to control their fertility, but find this too onerous. If somebody helps them and teaches
them, they might be willing to do things that they are unwilling to do when birth control is very costly.
Partly, the programs themselves, by helping women in such matters or couples in such matters as how to
bring up their children and how to make them healthier and how to make themselves healthier, stimulate new
patterns of living and new behavioral responses. The very strongly emphasized element in Cairo was insistence
on women's education as a key to this behavioral change. Also, access to non-pressure offered, broad range of
reproductive services.
ER: What was the basis for that new emphasis on women's rights in the context of world population?
PD: There is a strong political element and there is an element of westernization underlying this process.
Western feminists organizations' role was very pronounced in the Cairo proceedings and in the preparatory
process that went into it, which is a classic example of a cultural influence. Western feminists organizations' role
is significant in introducing new elements in the political agenda and posing demands that were not posed even
ten or fifteen years before.
Earlier models for the transformation of demographic behavior insisted on setting targets for population and
birth rates and trying to influence demographic behavior with fairly direct means. The classic example of this
was the Chinese policy that set specific targets and birth quotas and birth permits - the one-child policy. But
there were extremely large, if temporary, efforts of this sort in India.
There is a strong insistence nowadays that these direct efforts are counterproductive, and simply by helping
people do what they want to do anyway - namely, be healthier and educate their children better - will lead to
a spontaneous and voluntary modification of fertility behavior without any element of coercion.
ER: Were these coercive approaches counterproductive?
PD: It depends on the place. Now, bypassing the political question or how one should judge the system, the
rapid reduction of fertility in Communist China in a population that in its bulk remains poor and backward would
be probably impossible without rather heavy-handed policy measures.
When this was attempted by a less organized and less well structured political leadership, the results were
very much counterproductive: in India this effort -it being a democratic country - resulted in a resounding
defeat of the government, Indira Gandhi's electoral defeat. So the government backed down.
The notion that collective action can affect standards of expectations and pressure individuals is very
common in many fields of life. Sometimes it is informal pressure but every bit as effective. Few people in
Seattle would walk naked on the street because there is mutual expectation of what living in a society demands
from you. And it can be extended to such matters as how many children do you have. Or, it can be legalized:
people are supposed to have only one spouse although some would like several. Well, society does not permit
this. In principle, fertility need not be an exception from such rules; namely, that if there is an overriding social
interest to demand certain patterns of behavior, well, that can be done.
This is not the philosophy that the international agencies or any government likes to adopt. There is an
insistence that everybody has a basic human right to have as many children as they wish, but there is that little
addition that they should be free to choose responsibly. And what is responsible is a legitimate matter for
collective decision.
On the other hand - and nobody said this in Cairo much - some of the more signal historical examples
of controlled fertility, declining birth rate, were in fact in societies that were rather heavily male dominated. In
the modern era, Japan is an example of that. It is not exactly a society built on feminist principles, yet after the
Second World War and even before that, Japanese fertility declined way below replacement level.
So it is difficult to have a hard and fast rule that applies everywhere. I would say that many of the feminist
demands should be looked at then on their own merit. Educating women and not murdering female babies and
not discriminating in how food is allocated to children according to sex are totally sound demands, and if they
have a demographic payoff, so much the better.
But the demographic adjustment is something that can happen under a variety of circumstances, including
men realizing that fewer children is in their own interests. France, would be a case of such a family system;
namely, males finding that their responsibility towards the family can be better discharged if they have fewer
children.
And some of the feminist demands, to the extent that they loosen up the family system, can have an effect
that is economically less than beneficial. Certainly a good deal of the spectacular success of the East Asian
economy was based on a very strongly knit families where there was a division of labor and cooperation
between husband and wife, basically a patriarchal family. Which may not be ideal for every member, but
certainly provided very rapid growth of economic change. And eventually such healthy economic development
does benefit everyone, including women. They do end up to go to high school and eventually to colleges, and
they do end up to be favored because families became sparse.
ER: We have seen Taiwan and Singapore come through the other end of this demographic adjustment; has
womens' lot been improved in these countries?
PD: Certainly. Because once families have only two children and if one or both happens to be girls, there are
more pressures than when there are seven children with three of them boys and four of them girls and the boys
get all the attention - Singapore's per capita income is no higher than Australia's - and that means that
people, including girls, have longer education. Eventually economic and social advancement is what brings
greater power economically and socially to women.
ER: Thomas Malthus argued that the human population would be limited by food production and that war and
disease would result from overpopulation. How do you respond to the argument that Malthus was wrong in
1810, and he will be wrong in 2010?
PD: It's a complicated thing because Malthus himself evolved. The most popularly known Malthus, the young
Malthus with his 1798 essay, assumed that there is an elemental force, an attraction between the sexes, and
fertility is high, and the only thing that regulates population change is adjustment in the death rate.
But the more mature Malthus understood that people do not behave in their reproduction like an animal
species; there is a cultural overlay that can feed back on what people do. And acquisition of new ideas and of
institutions that favor individual decision making and make people responsible for running their own life feed
back into changing fertility behavior. So Malthus has more than one, face in this matter.
As to the debate whether a growing population can be supported, even there, the classic original Malthusian
formulation which saw the capacity to feed as the regulating factor in population growth can be and has been
replaced by the shifting definitions of what is adequate and acceptable. If a family finds a living arrangement
where everybody sleeps in the same room, even if the family consists of ten people, it is a very different society
where couples develop the notion that they must have privacy and the children have some element of their own
private space too. Those considerations can be felt as constraining as lack of food in determining what people
actually do, how they behave. So it is not by bread alone that people make these calculations. And these cultural
and ideational shifts can be a very powerful shaper of demographic behaviors.
ER: What will determine how many people can be supported by the Earth? How can we guess at its carrying
capacity?
PD: There is very often a lack of appreciation of the very changed magnitude of the equation here. For instance,
population growth rates have been declining since the late 1960s. At the same time, the absolute numbers added
to the human population are still increasing. At Malthus's time, a two percent annual growth rate would have
represented 20 million people, today the population is five times as much. So the absolute number of people is as
important or more important than the growth rate. Also, the formulation how many people can the earth feed, is
clearly the wrong formulation because what people aspire to is not mere survival but survival with creature
comforts and a pleasant environment. And the notion that growth can be sustained for long, without
compromising on those standards and those aspirations, is demonstrably wrong. So the question is not whether
the Earth can sustain twice today's population or even more, but would that twice as large population be as
much better off than it could be if the growth was slower or the population size was lower. That is a more subtle
calculation, but that is the relevant calculation.
Copyright 1995 Environmental Review