Tuesday 19 November 2013

Why do demographers keep under-estimating the size of peak world population?


Why do population projections keep underestimating the size at which world population is supposed to level-off, so that maximum population keeps getting revised upwards?


The answer is that demographic projections are typical of the social sciences in regarding all humans everywhere as interchangeable units (after controlling for age and sex differences) - and therefore the population projections have two false built-in assumptions:

1. That all populations in the world are the same in terms of psychology - and will therefore behave the same way given the same environmental stimuli.

This is false with respect to races, and also religions/ no religion.


2. That human psychology remains constant over time - that the population-relevant behavioural characteristics are not changing over time - not undergoing 'secular changes'.

This is also false. Since both are highly heritable general intelligence is declining while heritable personality is changing due to differential fertility (only slightly modified by differential childhood mortality - which is nowadays very low) - in ways that will reduce economic productivity.

Indeed, I believe (based on historical changes in simple reaction time data) that the rate of change in human psychology is very much faster (about twice as fast) as most people have so far assumed.


But as well as applying biologically due to natural selection, secular change in human psychology also applies at a societal level due to cultural selection - for example, secularization and apostasy have been a major reason for the collapse of fertility below replacement level in all developed countries.

Furthermore, the work of Eric Kauffmann shows that those religions, and especially traditional (anti-modern) denominations within religions, that support larger families are growing in their differential representation - which amplifies future population growth when offspring are retained within fertile denominations.


So we can be reasonably confident that the world population will keep growing until something stops it - famine and disease probably, backed by lethal violence, and perhaps (in the West) the novel phenomenon of mass suicide.

Or maybe the ruling elites will escape mass media influence, snap-out-of their Leftist psychosis, embrace real Christianity, and take sensible action to prevent the mega-horrors to come?

Ha! Only kidding...



Aquinas Dad said...

I am not sure where this is coming from. As a new visitor to the site (from Zippy's) is this a joke? Satire?
Estimates of peak world population keep being revised *downward*. The UN estimates of peak population have been consistently revising peak human population to occur sooner and be lower every five years since 1970.
Also, as someone who has interviewed Prof. Kaufmann (one 'f') his works, especially Shall the Religious Inherit the Earth?, all point to an effectively unstoppable sharp decline in world population in the near future which will serve to greatly magnify the influence and impact of the religious groups you mention.
Again, as a new reader I may be missing something, but you appear to have the central premise backwards.

Bruce Charlton said...

@AD - Maybe there are two stories going around. I am talking about the United Nations, mainly. But "an effectively unstoppable sharp decline in world population in the near future" is bizarre, if you mean in terms of normal demographic change. It may indeed happen, since we cannot long sustain the current population without major change; but only by the largest kill-off by several orders of magnitude in the history of the species. But if you aren't worried, then don't worry - far be it for me to spread doom and gloom when nothing will be done to avert d&g either way...

Aquinas Dad said...

I am sorry, sir, but there will be no mass die-off, no plague, no massive war for human population to peak and then naturally decline, rather rapidly, after a relatively short plateau.
The UN once said human population would peak at 28 billion in 2150. Them 14 billion in 2100; then 10; then 9.5 billion in 2080; them 9 billion in 2070; then 8 billion; then 8 billion in 2050; etc.
The fact is, serious demographers, such as Kaufmann, were very clearly predicting a natural human peak population, short plateau, and then relatively rapid decline in the 1970's based upon the already-changing fertility dynamics of much of the world. This is why each revision of the UN's world population prediction has always moved their 'highest confidence' predictions of how high human population will peak lower and when it will peak sooner.
Indeed, we may well be experiencing effective peak human population *right now*, the beginnings of the 20-25 year population plateua before a rapid, natural, non-violent decline in population.
Total Fertility Rate has been below replacement levels (meaning the next generation will be smaller) for many reagions of the world for more than a generation. Places like, Oh, Europe. North Africa. Asia. because of the US being right at replacement for some time, North America as a whole is - also below replacement for some time. And South America.
Leaving only sub-Saharan Africa. Or, well, parts of sub-Saharan Africa. Usually the violent, poor parts where replacement fertility is much higher than the West and local populations are lower to begin with.
Interestingly, even these fertility numbers may be skewed too high. Why? Higher fertility in that part of the world = more aid from the West.
Oh, don't worry! If you like doom and gloom there is plenty to go around. Who will care for the much larger Boomer generation when they ar in their dotage? How will markets and economies react when markets will be shrinking for the next 1-4 generations? How will governments react to a perpetually shrinking tax, voter, and labor base?
Not only is overpopulation a myth, it is distracting us from the very real impact of the coming population decline.

Bruce Charlton said...

@AD - http://esa.un.org/wpp/Documentation/pdf/WPP2012_%20KEY%20FINDINGS.pdf

I suppose it all boils down to whether someone thinks that two and a half billion extra people is a lot. And whether 'people' are just 'people' or whether it matters what specific people they are. And whether someone thinks the world economy is getting better or worse. And whether the necessary sci-tech breakthroughs are going to come, or not - whether we are on the up-curve or not. Whether developed population media ages mid forties and rising while other places are in middle to late teens is a problem, or not.

The significance of demographic change isn't 'Math' - oh no... Demographic change is natural selection in action on humans. We are living in a period of the most rapid and large scale demographic/ migrational changes in human history/ the most rapid natural selection on humans - our species is changing very fast.

It's off the map!

Aquinas Dad said...

Of course, in this paper
written in 2002 the UN predicted that 75% of the developing world would be below replacement fertility by 2050.
Fascinating; the Second Demographic Transition truly will change everything.
Especially since scholars determined that the UN had underestimated how many developing nations were ALREADY sub-replacement
a trend that was confirmed to be accelerating faster than the 2002 predictions.
So, again - the UN has historically guessed too high and too far into the future on population trends. This shows no signs of ending.
And if this is natural selection at work, and it may very well be, what does it tell us?
It tells us that a secular liberal ideology is a failure.

Crosbie said...

Does anyone have numbers for the absolute numbers of births globally per year, going back some years?

Calogrenant said...


Greg Cochran has had interesting thoughts on related themes.

Bruce Charlton said...

What I find bizarre is that when most intelligent people discuss world population they talk about rates and percentages rather than absolute numbers; and talk about very long term stabilization and decline rather than the peak which lies between now and then.

I persist in believing that a billion is a lot of people, and that when you add a billion to the world then this requires some development of resources.

1804 1 billion
+123 years
1927 2 billion
+33 years
1960 3 billion
+25 years
1975 4 billion
+12 years
1987 5 billion
+12 years
1999 6 billion
+12 years
2011 7 billion
+14 years
2025 8 billion
+18 years
2043 9 billion

OK there is expected to be an extra two years (12 - 14 years) to add the next billion, and a a bit more for the billion after that - but in terms of the big picture, world historical terms - does it really make any difference.

It's not as if this is all theoretical stuff - I can see exactly what is happening to this extra population in my everyday life, year on year: I see it in the city and nation around me, I see it in declining income.

J. B. said...

Dr. Charlton, let's say for the sake of argument that something will be done to address the reality of 2 billion more people... what is that you would want done?

Most people I know who express worry about overpopulation want people to stop having kids, have abortions, maybe murder the elderly and sick ("euthanasia"), and also coercively redistribute more and more resources from the wealthy and productive to the poor and unproductive. Since you reject all of these proposals I'd like to know what you would propose instead as a way of averting the dangers of overpopulation.

Calogrenant said...

"sensible action to prevent the mega-horrors to come"

Are you implying here you have some idea of what that sensible action might be? I must confess I have no idea of what even a rightly ordered leadership could do, what 'action' to take.

Bruce Charlton said...

@Jabes/ Calogrant - It cannot be averted.

Think of the coming disaster in terms of magnitude.

It can actively be made bigger and worse - which is what we are doing now, in almost every way possible (including the collapse of fertility in developed nations).

Or it can be reduced in severity, ameliorated - by stopping doing, and in most cases reversing, what we are doing now.

Crosbie said...

Absolute numbers of births are here: World Population Prospects: The 2012 Revision, under 'Births'. It indicates that peak births occurred during the period 1985-1990, and are now slightly down on that. The big trend seems to be a fall in the East Asian birth rate, and a corresponding large rise in Africa.