In epidemiology, we have a concept called the “epidemiologic transition,” which illustrates the shift in the the causes of illness and death as humans change from pre-agricultural to agrarian to affluent societies (Omron, 1971).

Traditionally, humans die from infectious causes, limiting their lifespan to a few decades at most. Through agriculture, they are able to increase their nutritional profiles, reducing infant mortality and allowing rapid population increases. As societies introduce efficiencies in transport and trade and move to technological solutions to former pathogen threats, infectious diseases become controlled and chronic conditions become more prevalent. Economic challenges restrict family size so that births and deaths reach equilibrium and population ceases to increase.

While it’s a great model for understanding the shifts in the health profile of worldwide or continental populations, it is fairly unsatisfying when examining within country or within community health and useless when looking at individuals.

The Health Transition and the Maasai

I’ve been thinking about a Maasai community in Laikipia, Kenya that I was working with this summer. We were looking at Q fever, a bacterial disease which can infect all mammals, but is particularly common in domesticated herd animals. The pathogen is transmissible to humans and can cause fevers, malaise, cardiac problems and miscarriages in pregnant women. It is an occupational hazard to those who work with animals, and potentially a threat to pastoralist communities, who depend on livestock for money and sustenance.

Now, it’s hard to know what was really happening before humans moved to agriculture for sustenance. Paleolithic peoples weren’t known for leaving written records or for data collection. We can, however, look at hunter gatherers in Sub-Saharan Africa or South America to give us at least some idea of what human health was like before we started growing crops in fixed locations.

More relevant to the Maasai, we can look at nomadic-pastoralists, who rely on domesticated animals but move from place to place, and sedentarized pastoralists, who also rely on livestock, but reside in mostly fixed locations. Sedentarization can occur due to land constraints which might include scarcity of water or the introduction of political or property boundaries.

Research has indicated that sedentarized pastoralists are more unhealthy than still nomadic livestock herders. Women and children in sedentary communities have been shown to have poorer nutritional profiles than nomads (Nathan, Fratkin et al. 1996, Fratkin 2001). Incidence of diarrheal and respiratory disease is lower in nomadic children than in children in sedentarized communities. Sedentarism and interaction with commercial livestock markets has been associated with declines in social cohesion, which has been associated with declining health profiles of pastoralist communities in Uganda (Pearson 2010). Sedentarization isn’t all bad, however. Nomadic communities have been found to be at greater risk for zoonotic diseases (like Q and Brucellosis), have lower rates of vaccination, poorer vitamin profiles and high rates of infant mortality(Montavon, Jean‐Richard et al. 2013).

The Direction of the Health Transition in Pastoralist Communities

In actuality, it is difficult to quantify “health,” though if we take infant mortality and life expectancy as an indicator of the quality of life of communities, we might find that sedentarized pastoralists do worse than nomadic pastoralists. This contradicts the “epidemiologic transition,” which posits that any shift towards fixed agrarian societies is beneficial to human health.

Modern societies, characterized by technological efficiencies, diversified economies and sophisticated transportation networks are significantly better for human health than nomadic hunter-gatherer contexts and pastoralist communities which exist at the mercy of weather and environmental pressures. Though it is definitely tempting to romanticize the days when humans quietly roamed the grasslands of Africa, eating whatever was available to them, it is hard to deny that humans were better off in a distant past. This would confirm the model of the epidemologic transition.

However, I believe, that though the trajectory toward development may be beneficial in the long term, the disruptions which occur along the transition have deleterious effects on humans health. I found this in Laikipia. Within a Maasai community, there were two distinct groups of people. One held on to traditional herding techniques and relied heavily on traditional medications to treat animals health problems. They mostly refused to send their children to formal school, had large numbers of children, and seemed ambivalent toward household economic diversification. The other was characterized by smaller families, eagerly sent their children to receive formal education, were open to modern herd management techniques and often took jobs or started business to diversify their household economic activities.

I found that those resistant to sedentarization and economic integration with the Kenyan market economy did significantly worse than those who embraced change. I collected data on herds, asking households how many animals they possessed, what kinds, how many were born in the past year and how many died. What I found was that households which engaged with the Kenyan market economy through formal employment as security guards or herders on large commercial ranches had larger and more diverse herds since they did not have to sell animals to obtain cash for health services or school fees. They sprayed their animals for ticks more often and they overwhelmingly reported fewer animals deaths as a proportion of their total herd, indicating that herds were healthier overall.

If we were to take animal health as a proxy of human health (as herding households are in maximal contact with livestock at all times), then we might see that the epidemiologic transition among the Maasai might not be linearly increase consistently, but might rather be J-shaped. Health might decline on the shift from purely nomadic to sedentarized, by might improve again as households adapt to new conditions. Thus, the pattern of the epidemiologic transition, while holding overall, might experience a series of dips along the way, presumably representing disruptions and adaptation to new conditions. It will be interesting to formally test this hypothesis.

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