Thesis #45 – Our ancestral hunter-gatherer populations had generally low population densities, and thus low effective population sizes, which produced relatively early cessation of aging at relatively high function due to genetic drift.
With very low population densities among our ancestors, the effective population sizes of hunter-gatherers was probably much lower than the total census population size of our species. Without question, the total human census population size has been growing since agriculture was first adopted. Coupled to this have been progressive improvements in transportation, making it possible for humans to travel hundreds of miles in their lifetimes thanks to the roads and waterways of agricultural civilizations. Thus, overall, the effective population sizes of hunter-gatherers were substantially lower than that of civilized human populations.
This, by itself, leads to the evolution of an earlier age at which aging stops, as already discussed in these theses. The point is that smaller effective population sizes are subject to less evolutionary “reach through” to higher chronological ages. This means that the forces of natural selection are further weakened at later adult ages, allowing an earlier cessation of aging. This is a numerical result derived from formal theory, so expect to find it relatively hard to intuitively assimilate.
There are present-day human populations that have lost hunter-gatherer patterns of demography and selection only in historical times, in such remote areas as upland jungle New Guinea for less than a century. Among such populations, aging is likely to cease during the age-range that we refer to as “middle age,” perhaps between 45 and 65 years of age. Thus, if such individuals were given regular access to food and good quality medicine, yet continued to sustain hunter-gatherer patterns of activity and feeding, they could enjoy long-sustained lives of reasonable health. At least until they die of homicide or the attack of a large carnivore.
That is, among present-day humans, there are some populations that, if they combined their ancestral hunter-gatherer lifestyle with the medical and law-enforcement benefits of modern civilization, could sustain function for many more decades than those of us with agricultural ancestry can. This possibility is strongly suggested by the epidemiological data that Steffen Lindeberg compiled in his 2010 book, “Food and Western Disease.” The indigenous populations that he has studied show remarkably low rates of chronic age-associated disease, from cardiovascular disease to cancer to diabetes. At least that is there pattern so long as they do not adopt a Western diet.
When these hunter-gatherer-ancestry individuals adopt Western diets, they show a pattern of age-associated disease at least as severe as that of Western populations leading a Western lifestyle, and often more so. The obvious evolutionary prescription that can be derived from the 55 is that these individuals should revert to their ancestral lifestyle, at least with respect to diet and activity. Lindeberg presents case-studies where this has been done, yielding a remarkable improvement in chronic health conditions among such individuals. This would be analogous to shifting cereal chow-fed cats back onto their normal diet of animal prey. Animal species will live longer on diets and activity regimes to which they have long adapted, humans included.