Sunday, December 18, 2005

Larger-scale Patterns In Global Demography

Guest Post by Steven Earl Salmony
Awareness Campaign on the Human Population

Note: These views do not reflect the general approach to demographic issues as we see them on this blog, but in the interest of general debate and of giving Stephen a little more opportunity to air his views we are putting them online.

Imagine for a moment that we are looking at an ocean wave, watching it move toward the shore where it crashes finally at our feet. The wave is moving toward us; however, at the same time, there are many molecules in the wave that are moving in the opposite direction, against the tide. If we observe that the propagation of the human species worldwide is like the wave and the reproduction numbers of individuals or certain countries are like the molecules, it may be inaccurate for the latter to be looked at as if it tells us something meaningful about the former.

Abundant research indicates that most countries in Western Europe, among many other countries globally, have recently shown a decline in their rates of human population growth. These geographically localized data need not blind us to the fact that the absolute global human population numbers are skyrocketing. The world’s human population is like the wave; the individual or localized reproduction numbers are like the molecules.

Perhaps a "scope of observation" problem is presented to everyone who wants to adequately understand the dynamics of human population numbers.

Choosing a scope of observation is a forced choice, like choosing to look at either the forest or the trees, at either the propagation numbers of the human species (the wave data) or localized reproduction numbers (the molecular data). Data regarding the propagation of absolute global human population numbers is the former while individual or localized reproduction data are the latter.

From this vantage point, the global challenge before humanity could be a species propagation problem. Take note that global propagation numbers do not vary with the reproduction data. That is to say, global human propagation data and the evidence of reproduction numbers of individuals in many places, may be pointing in different directions. The propagation data are represented by the wave; the reproduction data are represented by the molecules moving against the tide.

In the year 1900 world’s human population was approximately 1.2 to 1.6 billion people. With the explosive growth of the global human population over the 20th century in mind (despite two world wars, ubiquitous local conflicts, famine, pestilence, disease, poverty, and other events resulting in great loss of life), what might the world look like in so short a period of time as 41 years from now? How many people will be on the planet at that time? The UN Population has recently made its annual re-determination that the world’s human population will reach 9.2 billion people around 2050, and then somehow level off. No explanation is given for how this leveling-off process is to occur.

We can see that the fully anticipated growth of absolute global human population numbers is about 8 billion people between 1900and 2050.

Whatever the number of human beings on Earth at the end of the 21st century, the size of the human population on Earth could have potentially adverse impacts on the number of the world’s surviving species, on the rate of dissipation of Earth’s resources, and on the basic characteristics of global ecosystems.

For too long a time human population growth has been comfortably viewed by politicians, economists and demographers as somehow outside the course of nature. The potential causes of global human population growth have seemed to them so complex, obscure, or numerous that a strategy to address the problems posed by the unbridled growth of the human species has been assumed to be unknowable. Their preternatural, insufficiently scientific grasp of human population dynamics has lead to widely varied forecasts of global population growth. Some forecasting data indicate the end to human population growth soon. Other data suggest the rapid and continuous increase of human numbers through Century XXI and beyond.

Recent scientific evidence appears to indicate that the governing dynamics of absolute global human population numbers are indeed knowable, as a natural phenomenon. According to unchallenged scientific research, the population dynamics of human organisms is essentially common to, not different from, the population dynamics of other organisms.

To suggest, as many politicians, economists and demographers have been doing, that understanding the dynamics of human population numbers does not matter, that the human population problem is not about numbers, or that human population dynamics have so dizzying an array of variables as not to be suitable for scientific investigation, seems not quite right.

If I may continue by introducing an extension of my perspective.

According to the research of Russell Hopfenberg,Ph.D., and David Pimementel, Ph.D., global population growth of the human species is a rapidly cycling positive feedback loop in which food availability drives population growth and this recent, astounding growth in absolute global human numbers gives rise to the misperception or mistaken impression that food production needs to be increased even more.

Data indicate that the world’s human population grows by approximately two percent per year. All segments of it grow by about 2%. Every year there are more people with brown eyes and more people with blue ones; more people who are tall and more short people. It also means that there are more people growing up well fed and more people growing up hungry. The hungry segment of the global population goes up just like the well-fed segment of the population. We may or may not be reducing hunger by increasing food production; however, we are most certainly producing more and more hungry people.

Hopfenberg’s and Pimentel's evidence suggests that the magnificently successful efforts of humankind to increase food production in order to feed a growing population has resulted and continue to result in even greater human population numbers.

The perceived need to increase food production to feed a growing population is a widely shared and consensually validated misperception, a denial both of the physical reality and the space-time dimension. If people are starving at a given moment of time, increasing food production cannot help them. Are these starving people supposed to be waiting for sowing, growing and reaping to be completed? Are they supposed to wait for surpluses to reach them? Without food they would die. In such circumstances, increasing food production for people who are starving is like tossing parachutes to people who have already fallen out of the airplane. The produced food arrives too late; however, this does not mean human starvation is inevitable.

Consider that human population dynamics are not biologically different from the population dynamics of other species. Human organisms, other species and even microorganisms have essentially common population dynamics. We do not find hoards of starving roaches, birds, squirrels, alligators, or chimpanzees in the absence of food as we do in many "civilized" human communities today because these non-human species are not annually increasing their food production capabilities.

Please take note that among tribal peoples in remote original habitats, we do not find people starving. Like non-human species, “primitive” human beings live within the carrying capacity of their environment. History is replete with examples of early humans and more remote ancestors not increasing their food production annually, but rather living successfully off the land for thousands upon thousands of years as hunters and gatherers of food.

Prior to the agricultural revolution and the production of more food than was needed for immediate survival, human numbers supposedly could not grow beyond their environment’s physical capacity to sustain them because global human population growth or decline is primarily determined by food availability. Looked at from a global population perspective, more food equals more human organisms; less food equals less human organisms; and, in one and all cases, no food equals no humans.

Thanks for your careful consideration, rigorous scrutiny, and thoughtful comments.

Saturday, December 17, 2005

Evolutionary Theories of Aging and Longevity

Here are the Gavrilovs on this topic.

Evolution of Life Span

Now here's a useful slide presentation.

Longevity: The Biology and Demography of Lifespan

The book Longevity: The Biology and Demography of Lifespan by James R Carey, was published in 2003. The book:

presents the results of a monumental, twelve-year, National Institute on Aging-funded research project on the determinants of longevity using data from the life tables of five million Mediterranean fruit flies, the most comprehensive set of life table studies ever on the mortality dynamics of a single species. He interprets the fruit fly data within the context of human aging and the aging process in general to identify the determinants of mortality. Three key themes emerge: the absence of species-specific life span limits, the context-specific nature of the mortality rate, and biodemographic linkages between longevity and reproduction.

You can find an introductory chapter here.

Life Span: Evolutionary, Ecological and Demographic Perspectives

An interesting conference with the above name was held by CEDA back in 2001. You can find a full list of the papers given here.

Wolfgang Lutz and the Low Fertility Trap

Taking as his starting point the proposition that in the two centuries or so which have lapsed since the ending of the earlier Malthusian demographic regime (which occured more or less similtaneuosly with the arrival of the industrial revolution) no homeostatic demographic equilibrium has been achieved, the demographer Wolfgang Lutz has continued to dig away at the fertility issue to the point that he now feels compelled to ask the question whether or not those societies which may be characterised as experiencing low fertility (below TFR 1.5) may not in fact be caught in some kind of low fertility trap.

Lutz defines the basic Idea lying behind his hypothesis as being the following: once fertility falls below a certain level and stays there for sufficient time this can produce a self-reinforcing demographic regime change that is difficult or impossible to reverse. This 'low fertility trap' hypothesis is really based based on the operation of three interacting mechanisms:

1/. A population momentum component. The delay in childbirth produces very low fertility rates which last for decades, during this time there is pyramid-base shrinkage, and new generations arrive composed of much smaller cohorts. This systematically produces less and less children.

2/ An ideas propagation mechanism. This works via the idea of 'ideal family size': young people are increasingly socialized in an environment with few children, and this may result in a lower 'ideal family size' in the subsequent generation, and so on. Recent (2001) Eurobarometer readings from Germany and Austria indicate that young people may now, on average, have a below replacement ideal of family size (slide on page 8). Since preferences and expectations are important here, this can only lead fertility downwards.

3/ A negative economic feedback process due to cohort and other effects (the Easterlin thesis). Lutz, Skirbekk and Testa develop a flow chart model (page 7 of the presentation in the Adobe Acrobat) which attempts to describe this process.

Lutz's idea has its origins in:

(a) the observation that countries which have fallen below fertility his critical level of 1.5 TFR have generally not subsequently 'recovered' in the sense of returning to a level above 1.5. In particular the germ of the idea here comes from the work of the Australian demographer Peter MacDonald (see this paper) who was the first to note that 1.5 TFR seems to mark something of a watershed.

(b) an awareness that whilst most projections and policy were being set by the assumption that there was a likely 'homeostatic' return to near replacement fertility, there is no rigourous theoretical justification for this assumption.

As Lutz et al observe:

"Virtually all population projections for low fertility countries assume end of fertility decline at current cohort level (Eurostat) or increase (UN), while at the same time continued increases of life expectancy are assumed. To be honest: we have no good theory with predictive power. Some “soft” arguments: end of postponement, children make happy, governments will eventually do “something”. But at the same time the basic forces that brought down fertility continue to work, possibly even stronger (value change, globalization,youth unemployment)".

(c) the further observation that government policy has non-linear consequences in this area. This view differs, for example, from that of the Canadian sociologist Anne Gauthier who argues straight and simple that: Public policies have an undeniable effect on families. On the other hand it is close to the work of social network theorists who examine propagation mechansisms for ideas and values across societies. In the words of Ronald Rindfuss and his co-workers:

“Changes in attitudes likely create a feedback mechanism, influencing behavior; and changes in behavior likely create a feedback mechanism influencing attitudes.” (Rindfuss et al. 2004, p. 855)

In the terms of Lutz et al: once the number of children (siblings, friends, children seen in other families, media) experienced during the process of socialization falls below a certain level, their own ideal family size may become lower which in course may result in further declining actual family size and still lower ideals in the subsequent generation.

The idea of negative demographic momentum is closely associated with the other key contribution Lutz has made to our understanding of the "second demographic transition": his idea of a 'birth deficit'. This deficit arises due to the the continuing presence of a fertility tempo effect, wherby the increase in the mean age of childbearing results in a lasting loss of births, and these 'missing' births cause structural damage to the age pyramid.

In the main Lutz bases his economic feedback mechanism on the cohort impact theory of Richard Easterlin and his associated 'relative income hypothesis. According to Easterlin changing cohort size produces either a crowding-out (the baby boom) or a crowding-in (declining fertility) phenomenon. The hypothesis posits that, other things being constant, the economic and social fortunes of a cohort (those born in a given year) tend to vary inversely with the relative size of that cohort, which is itself approximated by the crude birth rate in the period surrounding the cohort's birth. The cohort mechanisms operate mainly through three main social institutions – the family, school and labour market. Diane Macunovich has a good summary of Easterlins ideas and their application to fertility changes in Relative Cohort Size, Source of A Unifying Theory of the Global Fertility Transition.

The operation of this general 'crowding mechanism' means that large birth cohorts face adverse economic and social conditions, higher unemployment, and lower than expected wages, outcomes which are significantly at odds with their material aspirations. As a result, they postpone family formation and have fewer children. This type of cohort analysis is now being applied to the 'greying' phenomenon in the United States as the large 'boom generation' steadily approaches retirement age. On the other hand, the crowding-in syndrome would mean that the reduced cohorts which follow the fertility decline should find work more easy to obtain, and salaries relatively higher. This should lead to rising income expectations, which may be more difficult to sustain as the fiscal burden weighs down on younger generations with the consequence that they continually postpone starting families.

This latter eventuality seems to have relatively little empirical evidence to date to back it up (except, perhaps, very recently in Japan) so should really be treated with some caution.

Macunovich takes the theory and tries to use it to develop a general theory of the whole demographic transition from cohort effects, and I feel that at this level the argument is not convincing. The cohort dimension is however very evident in the US baby-boom phenomenon, and the subsequent fertility reaction, and indeed this is having the consequence that population ageing is being seen very much as a cohort phenomenon in the United States, but this experience is hard to generalise.

Lutz et al do, however, offer another suggestive direction for analysis: low fertiliy leads to the acceleration of societal ageing, this produces cuts in welfare and pension benefits, generates a general pessimism about the future and lowers expectations about future income. The general pessimism, coupled with anticipations of increased life expectancy, can produce increased saving for the future, and this of course can produce a drag on current consumption. The drag on consumption produces a lethargic level of economic growth, and this induces young people to delay having children in order to attempt to maintain current income. This economic chain reaction, especially in the light of what is actually happening in Geramny and Japan, does seem to be one of the possible mechanisms through which the trap - should it in fact exist - might operate.

However, at the end of the day, as Wolfgang Lutz himself emphasises, what we need is more evidence. Perhaps we will find some in the next Eurobarometer survey on family intentions (due June 2006).


Rindfuss, Ronald R, Minja Kim Choe, Larry L. Bumpass, and Noriko O. Tsuya, 2004, Social Networks and Family Change in Japan , American Sociological Review 69 (December 2004): 838-861. Washington, DC: American Sociological Association.

Friday, December 16, 2005

What is This Blog

This weblog is written by a goup of demography enthusiasts. More explanation to come.

Blog Under Construction

What Is Demography Matters

Site Under Construction!

Thursday, December 08, 2005

The Postponement of Childbearing in Europe

At the present time some 66 countries have fertility rates which are below the level necessary for population replacement (TFR 2.1). Within the next decade the number of counries in this group is set to grow to the point where a majority of the world’s population will be living in regions where the existing population no longer replaces itself. This development in an of itself is no disaster - many countries arguably suffer from excessive rates of population increase - but equally reducing fertility too rapidly can lead to economic and social 'imbalances' that may well turn out to be, in and of themselves, 'undesireable'.

Understanding why this is happening has begun to present an important challenge for many areas in contemporary social science as there are evidently factors involved in the process which embrace areas as diverse as demography, sociology, anthropology, psychology, political science, economics and of course biology.

One of the characteristic features of this most recent fertility decline is that it is driven largely by a delay in childbearing: couples (and obviously in particular this means women) wait longer and longer before taking the decision to have a child. Understanding the dynamics behind this 'delay syndrome' is the key to developing a social policy to address the consequences, so it is particularly timely that the Vienna Institute of Demography was host last week to a Conference on this very topic: The Postponement of Childbearing In Europe. A number of interesting and important papers were presented, and I will be looking at a number of them between now and xmas. Indeed I have opened a page on my website which will be dedicated to the Conference.

But, just as a taster, why is postponment so important?

In the first place it is important to bear in mind that the currently registered low levels of fertility - and in particular what is known as lowest-low fertility (sustained fertility rates of 1.3 or below) - may not be taken to mean that completed cohort fertility is as low as it seems at first glance since what is involved is in part a temporal phenomenon (see this presentation by John Bongaarts and Griffith Feeney of the UN Population Council), and this temporal phenomenon gives rise to a measurement problem. Essentially women are both having fewer children, and at the same time they are also having them later, so in the short run there is a 'displacement effect' which tends to exaggerate the fertility (TFR) readings and fertility could eventually ‘recover’ to rather higher levels through increased childbirth at the older ages . However it is important to bear in mind that the postponment process has now been operating in many European societies for thirty or more years now, and it may continue for some decades yet (see this presentation by Joshua Goldstein and Wolfgang Lutz) so with very low levels of fertility operating for more than half a century the actual long-run 'equilibrium' level may be somewhat academic for a social and economic policy which needs to operate in the short to mid-term.

The debate of which this conference forms a part is important since, as I have already indicated, in recent years a general and progressive delay in the average age at first childbirth has been observed throughout the OECD world, and in particular in every European Union country. The percentage of births to mothers aged thirty or over now exceeds over 40% of total births in a number of countries, including Sweden, Denmark, Norway, Finland, the Netherlands, Italy and Spain. Indeed delayed first child birth is now considered one of the most characteristic features of the most recent fertility change, a fact which has lead some authors to talk of yet another demographic transition: the "postponement transition toward a late-childbearing regime".

Spain is a prime case here, since Spanish women are now the oldest first-time mothers in Europe, and arguably in the world, bearing the first child, on-average, at around 29. The position of Spain, however, is by no means unique. Women in at least six other European countries (Ireland, Italy, France, the Netherlands, Sweden, and Switzerland) as well as in Japan currently have their first child at an average age of over 28.

As I say the mean age at first birth in many 'late first birth' countries is, in fact, likely to continue to rise further in the near future, possibly eventually breaking the 30 year benchmark. A variety of factors lead demographers to suggest that it unlikely - at least in the short-term - that the mean age will increase much above this threshold with Czech demographer Thomas Sobotka concluding that a mean age of 32 may constitute something of an outer limit for the record late-first-birth pattern (at least with current assisted reproduction technologies).

In the meantime the issue which faces us is learning to live with the postponement process. That is what this and my subsequent posts on this conference are really all about.