Fear of the Dark

According to medical science, fearing the dark or fearing something you cannot see in the dark is considered a mental disorder. This condition is termed “nyctophobia.” However, a mild anxiety about darkness or about not being able to see something in the dark is human nature. No matter how courageous a person may be, it is nearly impossible not to feel uneasy while walking alone on a deserted path in the dead of night. Have you ever wondered what causes this anxiety or fear of the dark in humans?

Our ancestors, that is, primitive humans, had to fight against wild animals for survival. More than ninety percent of the sensory information the human brain processes at any given moment comes from the sense of sight. In humans, this most important sense—the sense of sight or vision—becomes ineffective in the dark, because there are relatively few photoreceptive rod cells in the retina of the human eye. These rod cells are what help us see as clearly as possible in darkness. The retinas of many wild animals, such as tigers and lions, contain many more rod cells than humans do, allowing them to exploit this human weakness and hunt primitive humans in the dark of night. Throughout the primitive era, humans were repeatedly attacked this way at night, witnessing death and losing their companions! These experiences left various imprints on their genetic information and caused genetic changes. We have inherited some of those altered genes over generations. Though we no longer have to battle wild animals for survival, these altered genes have influenced the structure and function of the neurons in the “semantic memory” (a special type of long-term memory in our brain that stores words, concepts, numbers, emotions, etc.), which has given us a natural, mild anxiety or fear of darkness or of things we cannot see in the dark.