Hunter-gatherer lifespan; Traditional life-expectancy

The average period an individual may expect to live among nomadic peoples who rely primarily on hunting, fishing, and harvesting wild foods.

Hunter-gatherers do not experience short, nasty, and brutish lives as some earlier scholars have suggested (Vallois 1961). Instead, there appears to be a characteristic life span for Homo sapiens, in that on average, human bodies function well for about seven decades. These seven decades start with high infant mortality rates that rapidly decline through childhood, followed by a period in which mortality remains essentially the same to about 40 years. After this period, mortality rates rise steadily until around 70 years of age (Gurven and Kaplan 2007). Of course, mortality rates differ geographically and temporally, especially in the risks of violent deaths and disease. However, these differences are minimal when compared on a global scale, and the mortality profiles of modern hunter-gatherers living in vastly different environments are remarkably similar.

We know specific details about modern hunter-gatherer lifespan from a few well-studied groups: the !Kung, Aché, Agta, Hadza, and Hiwi (Gurven and Kaplan 2007). Work on these groups show that approximately 60% of hunter-gatherer children live to age 15. Of those who reach 15, around 60–80% of them will live to age 45. If an individual lives to age 45, then on average they will live for approximately two more decades. However, not all modern hunter-gatherer groups show the exact same lifespan profiles. The average life expectancy at birth among these groups varies from 21 to 37 years, and the proportion of individuals living to 45 years old varies between 26% and 43% of the population. These individuals who live to age 45 then have a continued life expectancy between 14 and 26 years.

The generally low life expectancy at birth among modern hunter-gatherers is due to their very high infant mortality rates, which pulls down their average life expectancy significantly. Compared to the United States, infant mortality is over 30 times greater among modern hunter-gatherers, and early child mortality is over 100 times greater (Zopf 1992; Hill et al. 2007). Even late childhood mortality is about 80 times greater among modern hunter-gatherers. Not until the late teens does the relationship start to even out, with over a ten times difference in mortality. This difference then continues to decline until it reaches age 70, where mortality among modern hunter-gatherers is only three times greater than individuals of the same age living in the United States (Gurven and Kaplan 2007).

Given that the average human lifespan estimate was obtained from modern hunter-gatherer populations, does it represent the evolutionary history of our species, or is it simply the result of modern civilization impacting these groups (Washburn 1981)? Comparative studies predict a human lifespan of 66–78 years from regressions of lifespan on brain and body weight (Hammer and Foley 1996). Converted to average adult lifespan, these results overlap with the observed lifespan from contemporary populations. Similarly, a reestimation of several Paleolithic mortality curves shows a Paleolithic life course pattern similar to those of modern hunter-gatherers (Konigsberg and Herrmann 2006). These types of comparative studies as well as studies on modern hunter-gatherer populations support the conclusion that the evolved average adult lifespan for Homo sapiens is around 70 years and thus individuals living long lives in both traditional societies and developed countries is not simply the result of modern medicine and hygiene (Blurton Jones et al. 2002).

There are a number of hypotheses as to why human lifespan is so long and includes a lengthy postreproductive period. Two notable examples are the “embodied capital model” (Kaplan et al. 2000) and the “grandmother hypothesis” (Hawkes et al. 1998). The “embodied capital model” proposes that learning the complexities of hunter-gatherer feeding environments requires a long time to master but provides high benefits later in life, thus favoring an extended life span. The “grandmother hypothesis” suggests that humans live to old age so that women can invest time and resources in their grandchildren.

Excepting outside forces such as violence and disease, hunter-gatherers can live to approximately 70 years of age. With this life expectancy, hunter-gatherers are not dissimilar to individuals living in developed countries. One major area of difference is the high infant mortality rate of hunter-gatherers, which pulls down their life expectancy at birth and influences their overall average lifespan. This pattern of life expectancy among hunter-gatherers is not only a consequence of the impacts of modern civilization. Rather, humans appear to have an evolved lifespan of approximately seven decades that includes a lengthy postreproductive period.