Human population dynamics revisited with the logistic model: How much can be modeled and predicted?

Decrease or growth of population comes from the interplay of death and birth (and locally, migration). We revive the logistic model, which was tested and found wanting in early-20th-century studies of aggregate human populations, and apply it instead to life expectancy (death) and fertility (birth), the key factors totaling population. For death, once an individual has legally entered society, the logistic portrays the situation crisply. Human life expectancy is reaching the culmination of a two-hundred year-process that forestalls death until about 80 for men and the mid-80's for women. No breakthroughs in longevity are in sight unless genetic engineering comes to help. For birth, the logistic covers quantitatively its actual morphology. However, because we have not been able to model this essential parameter in a predictive way over long periods, we cannot say whether the future of human population is runaway growth or slow implosion. Thus, we revisit the logistic analysis of aggregate human numbers. From a niche point of view, resources are the limits to numbers, and access to resources depends on technologies. The logistic makes clear that for homo faber, the limits to numbers keep shifting. These moving edges may most confound forecasting the long-run size of humanity.