March 14, 2003
World Population May Shrink Later In 21st Century

Ben Wattenberg says UN demographers have finally accepted the extent of declining birth rates.

Now, in a new report, United Nations demographers have bowed to reality and changed this standard 2.1 assumption. For the last five years they have been examining one of the most momentous trends in world history: the startling decline in fertility rates over the last several decades. In the United Nations' most recent population report, the fertility rate is assumed to be 1.85, not 2.1. This will lead, later in this century, to global population decline.

Wattenberg and the UN demographers are almost certainly wrong in predicting a decline in the human population. If robots do not take over and if nanotech replicators do not run amuck and wipe us out then the human population will increase even late in the 21st century. Why? Aging rejuvenation therapies will cause a radical increase in life expectancy.

Increased life expectancy will increase the population in two ways. The most obvious is of course that people who live longer will not cause a population decline by dying off. The less obvious cause is that aging rejuvenation therapy will allow female reproductive organs to stay functional for a longer period of time. Women will be able to have children in their 50s, 60s, and later. Gene therapies will help repair aging cells and cell therapies will replace aging stem cell reservoirs. Also, the development of the ability to grow new organs will eventually include the ability to grow new ovaries and other female reproductive organs.

Another future contributing factor to the growth in human population will be the development of artificial wombs This will increase the fertility rate even among younger women who are too busy with their careers to want to be slowed up by a pregnancy. Consider the Hollywood actresses who can't get pregnant without putting their careers on hold. This is especially true for TV actresses who star in their shows. Filming goes on for too large a portion of the year to allow a pregnancy to happen. When artificial wombs become reliable many will opt instead to have their babies grown from their own cells but not in their own bodies. An artifiical womb will be more trustworthy than a surrogate mother because women won't have to worry about the artificial womb doing drugs, drinking alcohol, smoking, eating poorly, or getting an infection.

Natural selection is also going to eventually cause reproduction rates to rise. In a study of twins in Australia evidence was found for natural selection for genetically influenced traits that increase fertility.

University-educated women have 35% lower fitness than those with less than seven years education, and Roman Catholic women have about 20% higher fitness than those of other religions. Although these differences were significant, education and religion only accounted for 2% and 1% of variance in fitness, respectively. Using structural equation modeling, we reveal significant genetic influences for all three life-history traits, with heritability estimates of 0.50, 0.23, and 0.45, respectively. However, strong genetic covariation with reproductive fitness could only be demonstrated for age at first reproduction, with much weaker covariation for age at menopause and no significant covariation for age at menarche. Selection may, therefore, lead to the evolution of earlier age at first reproduction in this population.

Current highly visible trends are useful for predicting the future one or two decades in advance. But the further out a prediction is made the more other factors need to considered. Natural selection happens more slowly than changes caused by industrialization. But natural selection does happen and it is exerting selective pressure that is changing the behavioral and other characteristics of humans. At the same, the ways in which technology is changing society today are not the only ways technology will reshape human society tomorrow.

The two biggest wild cards that make future prediction extremely difficult for the 21st century will be the development of machine intelligence and the development of genetic engineering techniques for boosting human intelligence. These two developments will cause such huge changes in human society that predictions of demographers about human reproductive patterns 50 or 100 years from now are almost certainly very far from what will really happen.

It is still possible that the human population on Earth will decrease by the end of the 21st century. But it is unlikely to do so as a result of trends that demographers can now measure. Humans could migrate off planet in large numbers when space flight becomes widely affordable. Or a world government, responding to the development of biotechnologies that can rejuvenate and dramatically extend life, could enforce strict reproductive limits in order to prevent a rise in population. Or perhaps humans may all become part of a Borg mind that suppresses reproductive instincts in the individual nodes. Or a virus could be released into the population that does genetic alternations that in turn cause cognitive changes in human minds that make child-rearing unappealing. There are a lot of reasons human population could rise or fall in the latter part of the 21st century. The most important factors that will determine the outcome depend on technological developments that will happen as the century progresses. We can not know with sufficient precision how all these changes will play out. Therefore predictions of world population changes become increasingly inaccurate the further out the predictions are made.

Share |      Randall Parker, 2003 March 14 09:09 AM  Trends Demographic

Charlie Murtaugh said at March 17, 2003 5:07 PM:

As usual, I'm much more skeptical about lifespan enhancement, etc. than you are. But I'll confine my criticisms to one point: if you think that gestation is the main obstacle to career women having kids, I think you need to work with a few more women. In the labs I've been in, it's routine for pregnant women to work at the bench right up into the eigth month of pregnancy. The problem comes after the baby is born, when the mom wants to stay home -- even if she can afford a nanny or daycare. Perhaps in the City of the Future new moms can take a maternal-instinct-suppressing pill, before they hand their infants off to Roberta the Nanny Robot, or perhaps some cloned meat-puppet set to "Nurture," but that's a subject for another post on your part.

Randall Parker said at March 18, 2003 9:12 AM:

Charles, I'm optimistic about life extension therapies because the rate of progress in biological sciences is accelerating. Microfluidics, nanopore DNA sequences, increasingly higher capacity gene arrays, and assorted other advances are going to raise the productivity of biological researchers. At the same time, the number of people doing biological research will rise as more parts of the world industrialize and more economies can support the work of scientists.

Gestation: The women who do not become pregnant are more averse to the experience of pregnancy than the ones who do. There are women who do not want the burden. There are women who do not want to have a less sexy figure with stretch marks after the pregnancy is completed. There are women whose occupations (e.g. models, actresses, ballet dancers, professional athletes) are just not compatible with pregnancy. There are even women who fear pregnancy and the process of giving birth (I know a woman who never had children for that reason).

Priviledge Zanda said at November 5, 2004 10:18 PM:

Particulary less developed countries[LDC],are definitey going to exprience a decline in their population because of one of the following factors.

(a)Due to high rates of Infectious and Parasitic diseases,Inpaticular AIDS it is reducing every day,for example in ZIMBABWE there is a possibility that for every four people,one is HIV+.Majority of the population dont afford retroviral drugs to reduce the virulence of the disease.
(b)Poverty is also threatenig population increase by harnessing high mortality rates.Lake of balanced diet

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