Paleo Life Expectancy

Critics of paleodiet often claim that Paleolithic people died at 30 years of age or similar young ages, and suggest that this proves that paleodiet (basically, a grain-, legume-, sugar-, and dairy-free diet) does not support health or longevity. 

I would like it if these people would provide some evidence that meat, vegetables, fruits, and nuts lack some  critical nutritional factor necessary for longevity and found only in agricultural foods -- grains, legumes, sugar, or milk.  I do not know of any such factor. 

In fact, we can state certainly that paleolithic diets supplied humans with all the nutrients humans require, because if they did not, the human species would have expired due to malnourishment.  Further, as I showed in my post Primal Diet On A Shoestring, a paleo diet composed of modern foods can easily supply required nutrients.  This means that even if paleo people did have a short life expectancy, it was not due to some nutritional weakness of the paleolithic menu.

I consider the idea that paleo people died at 30 years of age (or so) a “just-so” belief derived from the stories that Mother Culture tells us.  I have never seen any evidence to support this claim.  On the contrary, critics commonly present this as something “everyone knows.”   So, how does “everyone” know this?  They learn it as a part of a pack of stories we get told about preagricultural people, all expressing the Hobbesian claim (made without evidence) that human life in the absence of agriculture and the State was “nasty, cold, brutish, and short.”

In short, "everyone knows" this the same way that "everyone knows" that cereal grains are essential to nutrition -- it is not knowledge, it is simple mythology.

As a matter of fact, we have evidence that hunter-gatherers had low adult mortality rates and achieved ages comparable to civilized people, despite the absence of the legendary longevity powers of agricultural foods and the tyranny of the State.



Recent Hunter-Gatherer Evidence

According to Between Zeus and Salmon: The Biodemography of Longevity, a publication of the National Academy of Sciences Commission on Behavioral and Social Sciences and Education (National Academy Press, 1997) (pages 176-179):

"The most reliable estimates of adult mortality rates available for a pre-contact hunting and gathering group are derived from Aché research (Hill and Hurtado, 1996), because of the research focus on producing accurate measures of age and accounting for all adults that lived during the twentieth century."

So what can we learn from the Aché?

Well, among them, 30-40% of people die before the age of 10-15 (most of these before 5). 

These early deaths draw down the average lifespan in hunter-gatherer tribes.  To simplify the mathematics, if you have a cohort of 100 babies, 40 of which die before 10 years and 60 of which die after 60 years, the average life expectancy for this group will fall under 40 years, despite 60% of the population living more than 60 years.

Among both ancient and modern hunter-gatherers, these and most adult deaths occurred from hazards of childbirth, infections, accidents (e.g. falling from a tree, drowning, etc.), animal attacks (insects, snakes, etc.), poisonings (toxic plants), inclement weather (floods, snowstorms, etc.) and other dangers affecting all age groups but especially children growing up in a wild environment.  They did not occur from diseases of civilization, like heart disease, cancer, diabetes, and the like.

Among the Aché, once people passed puberty, in the adult age range of 20-45 mortality rates appear low, about 1.5% per year.  In comparison,  adult wild chimps have a mortality rate of 7.9% per year.  The text states:

“Adult mortality rates remain low and do not rise significantly until the seventh decade of life, where the rate climbs to 5 percent per year and reaches 15 percent per year by age 75.”

This text supplies the following graph of the age-specific mortality rates among the Aché:

 

Aché age-specific probability of death, smoothed with logistic regression.

From this you can see that among the Aché, children under 10 and adults over 60 years of age have the highest death rates.  Some Aché people live into their 7th decade of life, despite lacking the assistance of civilization.  Males have a higher mortality rate than females due to accidents in hunting, more testosterone-induced reckless behavior,  and possible altercations.

This text also provides the following graph comparing probablities of surviving to ages up to 80 years among several human tribes--!Kung, Yanamamo, Aché, and Hiwi -- and wild chimpanzees at Gombe:

 

Age-specific probabilities of survival among human foragers and chimpanzees. 

You can see that wild humans can live about twice as long as wild chimpanzees, even have a chance of living past 80 years.  Regarding this data, the text states:

"Although sample size and methods of data collection vary among the four human groups, the survival curves show remarkable convergence, Although infant mortality rates vary, with Hiwi being the highest and Yanomamo the lowest, adult mortality rates between the ages of 20 and 45 are almost identical, about 1.5 percent per year. For that reason the survival curves are parallel to one another during the adult period. Chimpanzee survival curves, however, diverge dramatically from the human curves, due to a quite distinct adult mortality profile. For example, while both Hiwi and chimpanzees have about equal probability of reaching age 15, the conditional probability of reaching age 45, having reached age 15, is near zero for chimpanzees in the wild and about 75 percent among the Hiwi."

So modern hunters live well past 45.  What about ancient people?

Migration and Population Expansion Evidence

In preagricultural times (between 50, 000 and 10, 000 years ago), humans migrated out from Africa around the globe.  By 10, 000 years ago, humans had reached and populated the Americas.  Given human reproductive function, this could not have occurred if people died at 30 years of age.

In The Paleolithic Prescription, S. Boyd Eaton, M.D., Melvin Konner M.D., Ph.D., and Marjorie Shostak present data on reproductive milestones among recent hunter-gatherers.  Among three recent hunter-gatherer tribes (Agta, !Kung, Ache), the average age of menarche (onset of menses) is about 16 years of age, the average age of first live birth is 19.5 years, the average birth spacing is 3.45 years, and the average number of live births per woman is between 4 and 5.

In order for the human population to grow to populate all continents over the period 50K to 10K years ago, each woman (on average) would have had to have had more than 2 children who made it to adulthood and reproduction.

Taking the first live birth at 19.5 years,  an average birth spacing of 3.5 years, and a 30-40% mortality rate for children under 15, we can see that the average paleo woman had to live at least 60 years in order to see a growth in the total human population.

Lets do a thought experiment.  Say Patty Paleo has her first birth at 19.5 years of age.  This child, named Peggy Paleo will have a 60% chance of making it to adulthood.  If Peggy does make it to adulthood (menarche), Patty will be 35.5 years of age when Peggy first menstruates, and 39.0 years of age when Peggy has her first child.  Since Peggy will have to learn how to birth and care for a child from Patty, Patty will still be largely essential to Peggy’s survival until 39 years of age.

Patty Paleo will have her second birth at about 23 years of age.  If this second child, Rick reaches physiological adulthood (capable of reproduction, 16 years of age), Patty will have reached 39 years of age.

Two births only replace Patty and Paul, the parents of Peggy and Rick, assuming that both Peggy and Rick make it to adult hood.  Let’s say that Peggy and Rick do make it to adulthood.  To expand the population, Patty has to have at least a third child and raise it to adulthood.  So Patty has her third child, Darth, at 23+3.5=26.5 years of age.

Since about 1 in 3 children die before adulthood among the Aché, our thought experiment should include this aspect.  We will imagine that Darth makes it to 4 years of age, then dies of a snake bite.  Patty is now 30 years of age, and has her fourth child, Star. 

Patty will spend the next 16 years raising Star to adulthood, at which time Patty will be 46 years old. 

Data collected on the !Kung indicates that the average !Kung woman has 4 to 5 live births during her reproductive lifetime, with the last birth occurring in the woman’s third decade of life [1]. Therefore, we can imagine that Patty has a fifth child, Apogee, at 33.5 years of age.  Apogee will  reach 16 years of age, when Patty reaches 49.5 years of age.

The Menopause Evidence

Further evidence that paleo people, at least women, reached ages well beyond 50 years of age exists right now in the phenomenon of menopause, a reproductive milestone unique to humans among primates (elephants also have a menopause, and can live 70 years in the wild). 

According to evolutionary theory, menopause would not exist unless it conferred some survival advantage for offspring.  The fact that human females go through menopause around 50 years of age tells us that our ancestral mothers did in fact make it to 50 years and beyond, and that those mothers who ceased menstruating at about 50 years of age left more offspring (children and grandchildren) than those who continued to menstruate.  

In short, the fact that present-day human females go through menopause provides living testimony that our prehistoric ancestors had lifespans greater than 50 years, and that paleo people who lived more than 50 years made their offspring more successful (reproductively).

Photographic Evidence

Of course I could have simply showed you this photograph of Chief Seattle, a lifelong hunter-gatherer, made when he was somewhere near 85 years of age. According to the Wikipedia entry on his life, the Chief was born about 1780, and this photograph dates to 1865.

Clearly, those who say that paleo people didn’t live past 30 just don’t know the subject well enough to have an opinion.

For more on this topic, read Ron Hoggan’s excellent article, Life Expectancy in the Paleolithic.

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Notes:

1.  Frisch RE, Fatness and Fertility, Scientific American 1988 Mar;258(3):88-95.