Nineteenth century fever

Thermometer

A Stanford research group looks into why humans are cooler now.

The normal temperature of the human body is 37°C – or so you thought. That baseline was established in 1851, after a German doctor painstakingly gathered millions of temperature records. Yet, modern studies consistently yield a lower estimate, around 36.6°C. Does this difference come from 21st century thermometers being ever so slightly better than their 19th century counterparts, or have humans somehow lost 0.4°C over the centuries? A Stanford university group examined the question by pouring over US body temperature records starting back in the 1860’s – turns out, the army keeps a close eye on biological measures from certain recruits. The study shows that human temperatures have declined steadily by 0.03°C per birth decade. Are we slowly turning into cold-bloodied mutants then? Not so fast. This change possibly reflects a drop in our resting metabolic rate, the amount of calories we burn just to stay alive. This may partly come from improvements in general health, as the American population became less plagued by chronic infections that cause inflammation and quietly ‘rev up’ the body, such as tuberculosis, syphilis or gum disease.

Written by Elsa Loissel