In the nearly two centuries since 98.6 degrees Fahrenheit (37.0 degrees Celsius) was established as the standard ‘normal’ body temperature, it has been used as the measure by which fevers have been assessed. Over time, however, lower body temperatures have been widely reported in healthy adults — for example, in recent studies in the UK and the US. Researchers have now found a similar decrease among the Tsimane, an indigenous population of forager-horticulturists in the Bolivian Amazon.