A post from the author of the Finnish language book Evolving Humanity: "The replenishment rate required to keep a population stable is about 2.1 children per woman. The average fertility rate in a lot of industrialized countries is well below this - for instance, 1.58 in Canada, 1.42 in Germany, 1.32 in Italy, 1.20 in Japan and 1.04 in Hong Kong. The EU average is 1.51. Yes, in a lot of poor countries the figures are considerably higher - Niger tops the chart with 7.68 children per woman - but even then the overall world population growth is projected to start declining around 2050 or so. To give a sense of proportion: suppose that tomorrow, we developed literal immortality and made it instantly available for everyone, so that the death rate would drop to zero in a day, with no adjustment to the birth rate. Even if this completely unrealistic scenario were to take place, the overall US population growth would still only be about half of what it was during the height of the 1950s baby boom! Even in such a completely, utterly unrealistic scenario, it would still take around 53 years for the US population to double - assuming no compensating drop in birth rates in that whole time. We've adapted to increasing lifespans before. Between 1950 and 1990, the percentage of population over 65 almost doubled in Sweden, going from 10.3 to 18.1. (In the United Kingdom it went up from 10.7 to 15.2, in the US from 8.1 to 12.6, and in the more-developed countries overall it went from 7.6 to 12.1.) The beauty of economics is that like all resource consumption, having children is a self-regulating mechanism: if a growing population really does exert a heavy strain on resources, then it will become more expensive to have children, and people will have less of them. ... I see no reason to presume that radical life extension and indefinite youths would pose us any problems that we couldn't handle, at least not on the overpopulation front." You might also look at the demographic models mentioned in the Fight Aging! archives.