Replenishing our defensive microbes

Large‐scale characterization of the human microbiota has largely focused on Western adults, yet these populations may be uncharacteristic because of their diets and lifestyles. In particular, the rise of “Western diseases” may in part stem from reduced exposure to, or even loss of, microbes with which humans have coevolved. Here, we review beneficial microbes associated with pathogen resistance, highlighting the emerging role of complex microbial communities in protecting against disease. We discuss ways in which modern lifestyles and practices may deplete physiologically important microbiota, and explore prospects for reintroducing or encouraging the growth of beneficial microbes to promote the restoration of healthy microbial ecosystems. Exposure to microbes is known to train our immune system to recognize pathogens and promote host health. Here, we discuss how modern behaviors, including Cesarean sections, antibiotic use, and limited exposure to animals, might derail our microbiota from its ancestral trajectory, and discuss suggested methods to replenish beneficial human microbes.