Before electricity, night was something akin to the deep sea: just as we could not descend much below the water surface, we also could not investigate the night for more than a short distance, and for a short period of time. Things changed with two inventions: the Bathysphere to plumb the ocean floor, and electricity to light the night for sustained exploration. Exploration led to dominance, and night has become indistinguishable from day in many parts of the world. The benefits of electric light are myriad, but so too are the possible detriments of loss of dark at night, including poor sleep, obesity, diabetes, cancer, and mood disorders. Our primordial physiological adaptation to the night and day cycle is being flummoxed by the maladaptive signals coming from electric lighting around the clock. The topic of sleep and health has finally attained scientific respect, but dark and health is not yet fully appreciated.
