If we couldn't be afraid, we wouldn't survive for long. We'd be walking into oncoming traffic, stepping off of rooftops and carelessly handling poisonous snakes. We'd be hanging out with people who have tuberculosis. In humans and in all animals, the purpose of fear is to promote survival. In the course of human evolution, the people who feared the right things survived to pass on their genes. In passing on their genes, the trait of fear and the response to it were selected as beneficial to the race.
During the 19th-century debate surrounding evolution, the "face of fear" -- that wide-eyed, gaping grimace that often accompanies sheer terror -- became a talking point. Why do people make that face when they're terrified? Some said God had given people a way to let others know they were afraid even if they didn't speak the same language. Charles Darwin said it was a result of the instinctive tightening of muscles triggered by an evolved response to fear. To prove his point, he went to the reptile house at the London Zoological Gardens. Trying to remain perfectly calm, he stood as close to the glass as possible while a puff adder lunged toward him on the other side. Every time it happened, he grimaced and jumped back. In his diary, he writes, "My will and reason were powerless against the imagination of a danger which had never been experienced." He concluded that the entire fear response is an ancient instinct that has been untouched by the nuances of modern civilization [ref].
Most of us are no longer fighting (or running) for our lives in the wild, but fear is far from an outdated instinct. It serves the same purpose today as it did when we might run into a lion while carrying water back from the river. Only now, we're carrying a wallet and walking down city streets. The decision not to take that shortcut through the deserted alley at midnight is based on a rational fear that promotes survival. Only the stimuli have changed -- we're in as much danger today as we were hundreds of years ago, and our fear serves to protect us now as it did then.
Darwin had never experienced the bite of a poisonous snake, and yet he reacted to it as if his life were in danger. Most of us have never been anywhere near The Plague, but our heart will skip a beat at the sight of a rat. For humans, there are other factors involved in fear beyond instinct. Human beings have the sometimes unfortunate gift of anticipation, and we anticipate terrible things that might happen -- things we have heard about, read about or seen on TV. Most of us have never experienced a plane crash, but that doesn't stop us from sitting on a plane with white-knuckle grips on the armrests. Anticipating a fearful stimulus can provoke the same response as actually experiencing it. This also is an evolutionary benefit: Those humans who felt rain, anticipated lightning and remained in the cave until the storm passed had a better chance of not getting struck with thousands of volts of electricity. We'll look at ways in which we are conditioned to fear in the next section.