According to the researchers, there are several reasons why our bodies might be cooling down. One is improvements in temperature regulation. “We have air conditioning and heating, so we live more comfortable lives at a consistent 68°F to 72°F in our homes,” Parsonnet explains. “[I]t’s not a struggle to keep the body warm.”

A more significant factor might be the reduction of inflammation-causing conditions like tuberculosis, malaria and dental diseases, thanks to improvements in medical treatments, hygiene standards and food availability. “In the mid-19th century,” the study authors note as an example, “2–3 percent of the population would have been living with active tuberculosis.” And the prevalence of such diseases may have had a population-level impact on average temperatures.

“Inflammation produces all sorts of proteins and cytokines that rev up your metabolism and raise your temperature,” Parsonnet says.