THE EVOLUTION OF NUTRITION AND IMMUNITY: FROM THE PALEOLITHIC ERA TO THE MEDIEVAL EUROPEAN BLACK DEATH

To understand the biological effects of nutritional disruption on Native American immunity and fertility after 1492, it is necessary to consider what we know, and what we do not yet know, about three vital stages in human nutritional history. The earliest two stages affected the nature of human evolution. The first began more than 2.5 million years ago, when nutrient-dense foods from land mammals allowed an increasingly small human gut to complement an expanding brain. The second, according to a newer and more controversial hypothesis, took place between 200,000 and 90,000 years ago, when coastal marine migrations from Africa provided greater access to the omega-3 fatty acid docosahexaenoic acid (DHA). Those migrations contributed to what some scholars now describe as a second stage in the evolving growth of the human brain, due to the greater reliance on DHA as an exogenous nutrient. These evolutionary interactions, and their nutritional basis, coincided with a hunter-gatherer lifestyle and preceded the intensified farming of "Neolithic" foods such as wheat and corn, which began around 10,500 years ago throughout the world. We consider the rupturing of hunter-gatherer food systems as a third major stage in human nutritional history, beginning with the rise of Neolithic agriculture in Europe and Asia, and slightly later with the rise of maize intensification in parts of North America.

Assessing what we define as the third stage in human nutritional history allows us to consider how immunity, and thus demography, might be compromised by rupturing the food requirements that developed during the two earlier evolutionary stages. Scholarship on declining health markers and increasing disease in Europe and Asia during the Neolithic era, and slightly later during the rise of maize intensification in North America, offers an important model and conceptual framework to explain similarities and differences in post-contact North America, when populations were also faced with sudden changes to subsistence strategies and threats to their immunological health. There is still much that we do not know regarding the evolution of the human immune system, including the extent to which it continued to evolve and adapt during the rise of the Homo genus around two million years ago; or even the nature of the role of an immune system during the evolutionary divergence between vertebrates and invertebrates before that period. Nonetheless, we are comfortable with the suggestion that selective pressures may well have contributed to ongoing refinement of the inflammatory and immunological response during the Paleolithic era, coinciding with the development of a small gut in relation to a large brain, including in relation to the micronutrient and metabolic requirements for optimal immune function.

The brain utilizes micronutrients as well as energy. The former is required for the proper function of enzymes and other features that underlie chemical and hormonal signaling between the brain and the rest of the body. The relatively recent enlargement of the brain thus risked constraining the function of other parts of the body that preceded its evolutionary growth, including the cellular processes that allow the immune system to function against pathogens, or perceived pathogens. The consumption of nutrient-dense foods during the Paleolithic era thus allowed a smaller digestive system in relation to the enlarged brain, while also continuing to supply the immune system with all that it continued to require; or even with micronutrients and metabolic sources that allowed it to continue to evolve advantageously. If those micronutrient-dense foods were suddenly replaced with nutrient-poor foods, the consequences for optimal health, including immune function, would be deleterious. We ought to examine those consequences at relevant historical junctures. The problematic health consequences of the Neolithic transition to agriculture 10,000 years ago, for example, may have compromised immune function at just the point when the changing societal context made diseases more likely to proliferate. Examining that phenomenon provides a paradigm to understand the problematic curtailment of nutrient-dense foods in Native American history, particularly if we can inform our assessment of both historical phenomena and their mutual relevance with new insights from the fast-developing scientific literature on the association between nutrition and immunity.

The scientific literature on the link between nutrition and immunity has developed significantly since anthropologists and archaeologists first identified declining health in transitional Neolithic populations. It has evolved even further since historians such as Jones and Kelton began to highlight ruptured food access as one of several contingent factors in the decline of post-contact Native American populations. A vast number of human immune cells reside in the human gut. The immune response to pathogens that enter the body via the gut begins with these immune cells. Yet we have only very recently begun to realize the full extent of the inflammatory response that follows the gut's encounter with foods that are maladapted to its evolved structural and hormonal mechanisms: a release of inflammatory proteins that upregulate the human immune response, often chronically. It is likely that in such a chronically inflamed state, the efficacy of the acute immune response to pathogens is reduced. In this chapter we examine whether such a state was likely during the third stage of human nutritional history, which corresponded with the rise of Neolithic grains in Europe and the Middle East, and which also witnessed the proliferation of new diseases.

We take care to avoid overstating the importance of the concept of chronic inflammation, given that its scientific literature is still in its infancy, leading some in the sphere of functional medicine toward possible exaggeration or misunderstanding. Doing so will require examination of the optimal operation of the immune response to invading pathogens both in relation to and separate from the process of inflammation. We consider the connection between inflammatory health markers, declining working immunity to disease and the introduction of new subsistence patterns in the Neolithic Old World. Scholarship on these connections — including that which has examined Neolithic skeletal evidence — offers important models and conceptual frameworks to explain similarities and differences in post-contact North America, when populations were also faced with sudden changes to subsistence...