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The modern idea of stress began on a rooftop in Canada, with a handful of rats freezing in the winter wind.

This was 1936 and by that point the owner of the rats, an endocrinologist named Hans Selye, had become expert at making rats suffer for science.

"He would subject them to extreme temperatures, make them go hungry for long periods, or make them exercise a lot," the medical historian Mark Jackson says. "Then what he would do is kill the rats and look at their organs."