Everyone is to some degree afraid of the dark, because we’re evolutionarily programmed to be. During our tribal days, in the blackness—where our dull senses were essentially useless—we were easy prey for hunters of the night. Safety was with our people in a fire-lit camp.
When civilization progressed and we settled into homes, that fear stuck with us. And then it gave rise to one of the stranger and more little-known theories of Western society: Night air is poisonous.
Not only was venturing into the darkness and breathing in the evening ether terrible for your health, but so too was simply leaving a window open at night. It was such a powerful and pervasive myth that all the way into the early 1900s, many anxious Americans were taking every possible measure to seal their homes against the poisons of the evening, according to Peter Baldwin in his essay “How Night Air Became Good Air.”
But good lord, how did it come to this? Being afraid to venture out into the night and mingle with mountain lions and such is one thing, but fearing the air you require to live? It turns out that our ancestors actually did have good reason to be afraid of night air—but not for the reasons they imagined.
The myth is a component of miasma theory, which held that “bad air” emanating from decaying organic matter caused disease (an idea later replaced by germ theory). This was particularly bad around swamps, of course, and seemed to worsen at night. Said Catharine Beecher, the great American educator: “Thus it appears, that the atmosphere of the day is much more healthful than that of the night, especially out of doors.”