Since childhood, I have noticed that many of my peers are more afraid of the dark than I am. I learned early, when our family went camping, that if I allowed my eyes to adjust to the dark, I could see fairly well. I was taught that using a flashlight could make things seem worse. When using a flashlight, our eyes adjust to the amount of light the device casts, and we tend to see only what is illuminated by it. Everything else is shadow and mysterious. If one allows the eyes to adjust and walks through the forest without a flashlight, one can see much more, and the space around doesn’t seem as threatening. As a child, I loved to get up before the sun with my father. We would catch an early breakfast and get to the airport just as the horizon began to get light, taking off at dawn when the air was cool and smooth to fly in the mountains. Before I retired, I was often on call and had to rise in the middle of the night to respond to emergencies. I learned to enjoy driving and helping others when most of the community slept. These days, I rise in the night and do a bit of writing before returning to bed for a second sleep. I’ve been following that pattern for many years.

I haven’t completely erased my natural fear of the dark. I wouldn’t be comfortable walking alone in the dark in bear or mountain lion country, and I can be startled by unexpected sounds or unidentified objects.

Many human fears are the products of evolution, a slow process. In human history, those who ventured out at night were at higher risk of dying from big cats like lions, tigers, leopards, and jaguars, which hunt at night. The Tasmanian devil and the Nile crocodile also hunt during the dark hours. Humans who fell victim to nighttime predators didn’t pass on their genetic material, while those who stayed hidden at night were more likely to reproduce. Over many generations, evolution favored those who were afraid of the dark.

Scientists identify three types of behavior concerning dark and light. Nocturnal animals are those whose main activities are conducted at night. Nocturnal animals tend to sleep during the day. Owls, bats, badgers, mink, mountain lions, and timber rattlesnakes are all considered to be nocturnal animals. Other animals are labeled diurnal, meaning they are most active during the day and sleep at night. A third term, crepuscular, is reserved for those whose activities extend into dawn and dusk hours, is applied to some large predators, and is often used to describe human activities. However, most scientists believe that the fundamental biology of humans is driven by daylight.

The use of artificial light has altered human activity, but that is a relatively recent phenomenon in the evolutionary timetable. While humans have used fire and torches for hundreds of thousands and perhaps millions of years, portable lighting sources powered by electricity are relatively recent inventions. Human activities at night are primarily limited to indoor spaces. We tend to stay close to hearth and home when it is dark outside.

Of course, there are exceptions. A couple of miles from our home, there is an oil refinery that operates 24 hours a day. At night, the entire facility is bathed in artificial light. The square mile of primary activity is a place where it never gets dark. Crews of humans work there all night long, and those who are on the night shift sleep during the day. Most shift workers use blackout window shades to make their bedrooms dark during the day.

Other fears that humans have are rooted in our evolutionary history. Fear of snakes and spiders has come from generations of humans who have avoided or survived venomous bites.

Not all human fears are in proportion to actual threats. The odds of encountering a venomous snake in everyday activities are low. Even those bitten by snakes have a good chance of surviving with proper treatment. Very few humans in contemporary society fall prey to attacks by bears and lions. Our fears, however, remain with us. They have been passed down through our genetics.

Evolution is a slow process. It takes many generations for the majority of any population to adapt to new circumstances. Adaptation can occur more rapidly in species with relatively short life spans, but with humans, it takes many decades for evolutionary changes to become evident. During the time it takes, our fears can become out of sync with the threats to our lives. In terms of human survival, several objects in our environment pose a greater threat than the dark, snakes, and spiders. Handguns, automobiles, computer screens, and diseases pose much greater immediate threats to humans. Still, we tend not to be as afraid of those objects as we are of animals we are unlikely to encounter in our daily lives. Many people do not demonstrate fear of very real environmental threats. It remains to be seen how much human fears will evolve because evolution is a slow process.

No matter how much we try to apply logic to our fears, they are not entirely under our control. I startle easily when walking in the dark. I am nervous when walking through a dense forest at night. Now that I no longer have a job that takes me out at night, I limit my nighttime activities to my house and usually use lamps and other light sources when I am awake. Even when I wander about my house without turning on lights, there is light from the street lamp outside and various light sources within my house. Clocks on appliances provide light. Our house has light switches that emit light when turned off to make it easier to find them in the dark. I rarely bump into objects in my house, even when I don’t turn on the lights. Still, I am a bit more cautious. I walk more slowly and carefully, and listen to the sounds of my house and those that come from outside.

I hope that some of my confidence at night, a trait I learned from my father, has been passed down to our children and will be inherited by our grandchildren. I also hope they develop a reasonable fear of the dangers of modern living. Slow as it is, our evolution continues.