Thesis 44

Thesis #44 – Most of our ancestral hominin populations of the last million years benefited from increased forces of natural selection at early adult ages under conditions of relatively abundant nutrition derived from hunting, gathering, and cooking and an increased ability to defend themselves against predators, which led to the evolution of relatively slow rates of aging among humans.


We have already discussed possible causes for the wide variation between species in their patterns of aging.  Animals that have good protection from predators, such as shells or rapid flight, have slower rates of increase in their adult age-specific mortality when studied under protected conditions.  This is because they have evolutionarily benefited from a slower fall in their forces of natural selection, due to lower death rates in the wild during their previous evolution.

The hominin lineage that led to the evolution of contemporary humans had similar benefits.  We now exhibit much slower rates of increasing adult age-specific mortality compared to most other terrestrial mammals, even when we protect these other species in zoos, supplying them with food and veterinary care.  In this respect, we are like elephants and whales, which are also notably long-lived.  This raises the natural question:  what was our distinctive adaptation that gave us lower death rates in the wild?

The answer to this must lie in our adoption of proficient tool use and extensive social cooperation.  For much of the last million years, we have been a hunting animal that used sharpened stone at the tips or cutting edges of our weapons and other tools.  An armed group of us can easily defend ourselves against marauding predators, particularly when we throw spears and fire arrows, as such use of weaponry reduces the need to directly engage a potential predator.  This doesn’t mean that we were never successfully carried off by the occasional lion or tiger.  Solitary adult humans who are caught unaware can still be successfully attacked from behind by large carnivores, as can children.  But in armed groups we have long been relatively impregnable to attack by other terrestrial animals.

In addition, we are omnivores who extensively prepare our food, both cleaning and cooking it, as needed.  This has given us the ability to eat a wide range of foodstuffs, from practically any animals of significant size to a wide variety of plant parts, from fruits to tubers to nuts to seeds.

Finally, we have a much greater ability to anticipate dangers than other animals.  And we share knowledge of such hazards socially, thanks to language.

All these features of human ecology produced a general lowering of our adult death rates even before the advent of agricultural civilization.  For a very long time, our principal mortality risks have been contagious disease, physical accident, and violence toward each other.  Perhaps our greatest danger was our fellow man.  Contrary to certain Edenic myths, homicide and tribal warfare are common enough among hunter-gatherer populations that have not been conquered by civilized nations.

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