Autoimmune Diseases in the Interpretation of Evolutionary Medicine

Autoimmune diseases comprise a broad group of conditions that affect virtually any organ or tissue and share mechanisms of chronic, autoimmune-based inflammation. Once rare or unknown, they have become increasingly common in recent years, affecting individuals of all ages, including the elderly, due to the growing the number of older people. According to evolutionary medicine, if the frequency of a disease, or group of diseases, increases sharply over a few decades, the primary cause cannot be the effect of genetic alterations but rather the consequence of one or more alterations in the living conditions of the species. For autoimmune diseases, there is no environmental, dietary, or infectious factor that appears to correlate with their increased frequency. On the contrary, the epidemic of autoimmune diseases is likely correlated with serious alterations of our holobiont (i.e., our organism, the host species, plus the myriad of species coexisting with us). In particular, the critical factor appears to be the decreasing incidence of macroparasite infestations, without, however, excluding the effects of profound alterations in the bacterial ecosystems that are also part of our holobiont. The macroparasites modulate and curb the intensity of immune responses in order to survive in our bodies. In the coevolution of host organism and other species of the holobiont, a delicate balance has developed that is severely altered by the eradication of macroparasites. Therefore, it is necessary to move beyond the concept of macroparasites as harmful species by definition and therefore to be eliminated without hesitation. Alternatively, it is essential to study our holobiont as a whole and consider the balances of its ecosystems before modern alterations. Furthermore, it is essential to evaluate the effects of reintroducing macroparasite species with which we have coevolved into our holobiont.