The therapeutic power of placebo is well recognized. In fact, central nervous system (CNS)-body interactions can influence health, fertility, and even life span itself. We suggest that the placebo response might have been of importance in the evolution of the human species, once brain development reached a certain level. Some individuals may have positively responded to the placebo given by a primordial healer or by themselves, and markedly increased their health and well-being. Those individuals may have had an evolutionary advantage due to increased fertility, better physical performance and increased life span. We consider this enhanced "CNS-body interactions/placebo sensitivity" a biological trait that has been selected for through time. Being this a genetic trait, it is susceptible to bear polymorphisms and suffer spontaneous mutations, which would explain the well recognized interindividual variation in the response to placebo.
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