Hunter-gatherers lived in equilibrium with their environment just as every other species does. The oft-cited example is the !Kung Bushmen of the semi-arid Kalahari desert, who were studied by Richard Lee of the University of Toronto and a team of anthropologists in the mid-1960s. Their observations, Lee noted, were made during “the third year of one of the most severe droughts in South Africa’s history.” The United Nations had instituted a famine-relief program for the local agriculturalists and pastoralists, and yet the Bushmen still survived easily on “some relatively abundant high-quality foods,” and they did not “have to walk very far or work very hard to get them.” The !Kung women would gather enough food in one day to feed their families for the next three, Lee and his colleagues reported; they would spend the remaining time resting, visiting, or entertaining visitors from other camps.

The prevailing opinion among anthropologists, not to be confused with that of nutritionists and public-health authorities, is that hunting and gathering allow for such a varied and extensive diet, including not just roots and berries but large and small game, insects, scavenged meat (often eaten at “levels of decay that would horrify a European”), and even occasionally other humans, that the likelihood of the simultaneous failure of all nutritional resources is vanishingly small. When hunting failed, these populations could still rely on foraging of plant food and insects, and when gathering failed “during long-continued drought,” as the missionary explorer David Livingstone noted of a South African tribe in the mid-nineteenth century, they could relocate to the local water holes, where “very great numbers of the large game” also congregated by necessity. This resiliency of hunting and gathering is now thought to explain why it survived for two million years before giving way to agriculture. In those areas where human remains span the transition from hunter-gatherer societies to farmers, anthropologists have reported that both nutrition and health declined, rather than improved, with the adoption of agriculture. (It was this observation that led Jared Diamond to describe agriculture as “the worst mistake in the history of the human race.”)

Although famines were both common and severe in Europe until the nineteenth century, this would suggest that those with European ancestry should be the most likely to have thrifty genes, and the most susceptible to obesity and diabetes in our modern toxic environments. Rather, among Europeans there is “a uniquely low occurrence of Type 2 diabetes,” as Diamond puts it, more evidence that the thrifty-gene hypothesis is incorrect.

Species adapt to their environment over successive generations. Those that don’t, die off. When food is abundant, species multiply; they don’t get obese and diabetic.