A 2020 study from Stanford University has found that human body temperature - previously standardised at 37°C - has been steadily declining over the last 200 years or so.

Using historical records, the research team found that the current average body temperature is probably now around half a degree lower.

[…] we determined that mean body temperature in men and women, after adjusting for age, height, weight and, in some models date and time of day, has decreased monotonically by 0.03°C per birth decade."

See: Decreasing human body temperature in the United States since the industrial revolution

The drop is currently unexplained, but suggestions include : decline in physical activity, the effects of antibiotics, improved hygiene & etc.

Also see :Thermoregulationplugin-autotooltip__plain plugin-autotooltip_bigThermoregulation

"The core temperature of a human is regulated and stabilized primarily by the hypothalamus, a region of the brain linking the endocrine system to the nervous system, and more specifically by the anterior hypothalamic nucleus and the adjacent preoptic area regions of the hypothalamus. As core temperature varies from the set point, endocrine production initiates control mechanisms to increase or decrease energy production/dissipation as needed to return the temperature toward th…