The biological adaptations that allowed humans to inhabit cold environments — the metabolic capacity to generate heat, the physiological responses to cold exposure, the behavioral tendencies toward fire-making and clothing and shelter — were shaped by millions of years of selection pressure from exactly the kind of cold that threatened Jean Hilliard on December 20, 1980.

But while humans were adapting to cold, they were also dying from it, and the history of cold-weather fatalities is as old as the history of cold-weather living.

Soldiers have died of hypothermia in winter campaigns since armies first marched in cold weather.

Explorers have died of cold in remote territories since exploration began.

Workers, travelers, and the impoverished have died of cold in cities and in the countryside since industrialization brought populations into environments where the combination of inadequate clothing, inadequate shelter, and inadequate nutrition made hypothermia a constant danger.

The medical understanding of hypothermia — what it is, how it progresses, what can be done to reverse it — developed slowly through this long history.