In my last two posts, I have replied to the overpopulation objection to radical life extension, the most common objection to those of us who want to defeat death. While my defense of indefinite lifespans has so far centered around moral concerns, the computer scientist Alexandre Maurer has recently offered mathematical reasons to doubt the whole premise of the overpopulation objection to longer lifespans.
His main conclusion is that fertility rates and not longevity are the true culprits in population increases. A spectacular extension of life will have a negligible effect on population growth compared with a slightly greater fertility rates. To explain, he offers a simple example.
Assume an initial population of 1000 people. The fertility rate is 2, and the life expectancy is 80. Women give birth at 20. Now, let us consider two variations:
Case A: Death disappears. Nobody dies anymore!
Case B: The fertility rate slightly increases from 2 to 2.5.
Which of these two cases will lead to the greater population increase? A quick calculation gives the following results:
– After 500 years, the population will be 26 000 in case A, and at least 780 000 in case B: 30 times more than in case A.
– After 1000 years, the population will be 51 000 in case A, and at least 206 000 000 in case B: more than 4000 times case A! The gap will be enormous.
The point is that the disappearance of death “only causes a linear population increase; while a fertility rate slightly greater than 2 causes an exponential population increase.” And this means that early death is an inefficient means of population control compared to lower birth rates.
Another consideration is that:
There is an inverse correlation between fertility and longevity: population increases the most in the countries with the shortest life expectancy. The common cause is poverty: when infant mortality is high, there is an incentive to have many children to ensure that some of them eventually survive. In addition, when there is no retirement system, the only “retirement insurance” consists in having many children. Further, to this double incentive to have children, must be added the lack of access to contraception, and a lack of information about it.
The implication of all this is that “people concerned about overpopulation should focus on reducing inequalities and improving the standard of living of the poorest countries.”
In fact, in rich countries, underpopulation is more of a problem rather than overpopulation, and rich countries would benefit enormously from increased healthy lifespans. Moreover, since rich countries will probably be the first to benefit from life-sustaining technologies, “is very unlikely that increasing life expectancy will result in an overpopulation crisis; especially since such an increase will first happen in rich countries, where the fertility rate is low.”
Furthermore, better material security generally leads people to have fewer children. Remember too that a “even if we lived 1000 years, a fertility rate slightly lower than 2 (e.g.,1.9) is sufficient in the long-term to result in a decreasing population.”
So in addition to all the moral arguments I have made in my two previous posts, I add Maurer’s insight: fertility rates are much more significant in causing population increase than death rates.