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 w as tested and found wanting in early-20th-century studies of aggregate human populations, and apply it instead to life expectancy (death) an d fertility (birth), the key factors totaling population. For death, o nce an individual has legally entered society, the logistic portrays t he situation crisply. Human life expectancy is reaching the culminatio n of a two-hundred year-process that forestalls death until about SO f or men and the mid-80's for women. No breakthroughs in longevity are i n sight unless genetic engineering comes to help. For birth, the logis tic covers quantitatively its actual morphology. However, because we h ave not been able to model this essential parameter in a predictive wa y over long periods, we cannot say whether the future of human populat ion is runaway growth or slow implosion. Thus, we revisit the logistic analysis of aggregate human numbers. From a niche point of view, reso urces are the limits to numbers, and access to resources depends on te chnologies. The logistic makes clear that for homo faber, the limits t o numbers keep shifting. These moving edges may most confound forecast ing the long-run size of humanity.