Speculation on ancestral lifespan is fun and potentially illuminating, but I think examining living, albeit imperfect, examples of modern hunter-gatherers offers greater insight. Sure, the environment has changed, wild food sources have shrunk in diversity and availability, and modern civilization has encroached and meddled and disrupted, but the few remaining hunter-gatherer populations exhibiting relatively untouched traditional lifestyles represent the most promising window into what life actually looked like and how long it lasted for our ancestors. Luckily, a couple of researchers – Gurven and Kaplan – had the bright idea to look at ethnographic studies on actual, living HG populations and analyze the available data on actual lifespan and mortality therein. They found some interesting stuff.
This study (PDF) has been floating around for a while. Readers have sent it to me on several occasions, and I believe it’s been mentioned in other bits of the online ether (blog comments, etc). The earliest I saw it was over a year ago on Ryan Koch’s blog.
The populations they looked at were given classifications: hunter-gatherers; forager-horticulturalists; and acculturated hunter-gatherers. Hunter-gatherers were groups without significant contact with outside cultures and included the !Kung, the Ache, the Agta, the Hadza, and the Hiwi. Forager-horticulturalists hunted, gathered, and used some agriculture. They included the Yanomamo, the Yanomamo Xilixana, the Tsimane, the Machiguenga, and the Gainj. Acculturated hunter-gatherers/foragers had significant, steady contact with outside cultures and included Northern Territory Australian Aborigines, the Tiwi, and the Warao, as well as other !Kung, Agta, Hiwi, and Ache groups. Gurven and Kaplan also looked at Swedes from the mid 18th century.
On average, 57%, 64%, and 67% of children make it to 15 years among “untouched” hunter-gatherers, forager-horticulturalists, and acculturated hunter-gatherers, respectively. That makes perfect sense, given what we know about child mortality rates in HG populations. The “wildest” groups, the HGs, who rely on hunted and gathered food also experience the most childhood deaths, while the hunter-gatherers with similar diets but presumable access to certain modern trappings enjoy the best childhood survival. It’s important to note that the acculturated groups in this study were characterized by increased access to immunization and medical care, especially for children; acculturation of traditional peoples hasn’t always had such a beneficial effect on their health and longevity (consider the health of Native Americans relegated to reservations, white flour, sugar, and vegetable oil). In fact, first contact with industrial or “civilized” cultures usually resulted in a massive initial increase in childhood mortality (diseases, mainly; the Ache lost about 40% of their population to foreign disease), but post-contact was characterized by lower childhood mortality, even compared to pre-contact rates. Mortality reductions in contacted hunter-gatherers were greatest in childhood and declined as populations aged.
Of folks who hit age 15, the percentage of hunter-gatherers who make it to age 45 is higher than the percentage of forager-horticulturalists who make it to age 45, but not by much – 64% to 61%. Acculturated hunter-gatherers excel here; 79% of their 15 year-olds make it to age 45. You might even say the study’s acculturated hunter-gatherers were essentially Primal, eating and moving traditionally while enjoying access to modern medicine.
From age 45, the mean number of expected remaining years of life is 20.7, 19.8, and 24.6 for hunter-gatherers, forager-horticulturalists, and acculturated hunter-gatherers, respectively. Give or take a few years, they could all “expect” to live about two decades if they were still alive by age 45 – a far cry from a “nasty, short, and brutish” existence.
There was variability among different populations within each category, of course, and at a later date it might be worth it to examine the differences in lifespan and lifestyle (diet, illness, etc.) among, say, the Ache and the !Kung to see if they align with our Primal perspective. The Ache, for example, rely heavily on hunting, traditionally obtain upwards of 80% of their calories from animals, and have high levels of homicide (including infanticide and warfare with rural Paraguayans), and they tended toward greater adult mortality.
The authors have no allegiance to or interest in the Primal Blueprint diet, but we can glean a few things that relate directly to our interests. First, it demolishes the common refrain that hunter-gatherers all die young. Average life expectancy is marred by infant mortality rates, and it’s clear that hunter-gatherers – the closest analogues to our Paleolithic ancestors – can and do enjoy “modern” lifespans with an average modal age of 72 years.
Second, Gurven and Kaplan show that “degenerative deaths are relatively few, confined largely to problems early in infancy.” Heart attacks and stroke “appear rare,” and the bulk of deaths occur when the person is sleeping and are free of obvious symptoms or pathology. Most “degenerative” deaths are attributed to “old age.” “Illness” is the main cause of death among all age groups and all populations, except for the pre-contact Ache (supreme hunters), and the authors break illness into different categories. The big killers were infectious respiratory diseases, things like pneumonia, bronchitis, and tuberculosis. Gastrointestinal illnesses also did a number on them, accounting for 5-18% of deaths, with diarrhea (probably stemming from parasites and coupled with malnutrition) taking the lion’s share. Violence was also a significant killer.
Third, and this is crucial, it destroys the other common argument that an evolutionary diet high in animal products might still be harmful because we didn’t evolve to live past forty, which is when diet-related diseases begin to show. Gurven and Kaplan make an extremely salient point: since the bulk of human evolutionary history took place over the course of 2 million years prior to the advent of agriculture, and that pre-agricultural period conferred most of the “major distinctive features of our species, such as large brains, long lives, marriage and male investment in offspring,” it’s likely that the “age-specific mortality pattern” of human beings also evolved “during our hunter-gatherer past.” That is, they propose that the human potential for longevity is not a product of modern living; instead, it appears to be a genetic characteristic shared by all Homo sapiens. Advances in medical technology bolster and support that inherent longevity (as shown by moderate lifespan increases in acculturated hunter-gatherers and modern industrial populations), but they aren’t responsible for it.
This data shows that human longevity is not a product of modern living. It shows that we have inherent proclivities toward long life, as long as we satisfy certain criteria – namely, the steady acquisition of food and shelter and the avoidance of infection, trauma, illness, and violent injury. The evolutionary lifestyle that eschews modern industrial processed food and promotes healthy levels of activity is the same one that supported our evolution into long-living Homo sapiens. Modern technology, sanitation, and medical advances are merely the cherries on top of an already solid framework.