Evolution, the Immune System, and the Health Consequences of Socioeconomic Inequality

Abstract

Healthy development and function of essentially all physiological systems and organs, including the brain, require exposure to the microbiota of our mothers and of the natural environment, especially in early life. We also know that some infections, if we survive them, modulate the immune system in relevant ways. If we study the evolution of the immune and metabolic systems, we can understand how these requirements developed and the nature of the organisms that we need to encounter. We can then begin to identify the mechanisms of the beneficial effects of these exposures. Against this evolutionary background, we can analyze the ways in which the modern urban lifestyle, particularly for individuals experiencing low socioeconomic status (SES), results in deficient or distorted microbial exposures and microbiomes. Thus, an evolutionary approach facilitates the identification of practical solutions to the growing scandal of health disparities linked to inequality.

Keywords: brain development; evolutionary biology; immune dysfunction; immune regulation; microbiota; socioeconomic status.

FIG 1

A simple classification of the variety of inputs provided by microbes that influence organ development, physiology, metabolism, and the immune system. References are in the main text. LPS, lipopolysaccharide.

FIG 2

Factors associated with low SES that have profound effects on microbial exposures and on the composition of the microbiota and the consequent microbiota-mediated effects on health. References are in the main text.