Skip to navigation | Skip to content

Some fears are inherited

Genetics may have something to do with whether you fear a situation

Fear, long thought to be a learned response, may actually be a partly inherited trait programmed into our genetic makeup, a study of twins has found.

Dr John Hettema of Virginia Commonwealth University in Richmond, Virginia, and Swedish colleagues studied 90 pairs of identical twins and 83 pairs of fraternal (or non-identical) twins enrolled in the Swedish Twin Registry. Their report appears in the latest issue of the journal, Archives of General Psychiatry.

Identical twins have exactly the same genes, but fraternal twins are genetically different - as different as children born separately from the same parents.

In the study, the twins were shown a series of different images, some naturally frightening, such as snakes and spiders, and others neutral, such as circles and triangles. The subjects were also given a mild electric shock while viewing some of the images.

During the tests, the researchers measured the subjects' skin electrical conductivity, which normally increases in states of anxiety and fear due increased output from sweat glands. When the results were analysed, the researchers found that the identical twins had the same responses; but the non-identical twins had differing responses.

Traditionally, fear has been thought of as a learned response. A person undergoes a frightening experience and then learns to be apprehensive and anxious when it happens (or may happen) again, Hettema said. The process is known as conditioning.

"Now can say that the fear conditioning process in humans is controlled, at least to some extent, by genetic factors," he said. Between one-third and one-half of the fear conditioning process appears to be inherited, he added.

Fear is a natural and desirable response to a dangerous situation. But when a person's fear is out of proportion to the stimulus that caused it, or is chronic or debilitating, a person can be said to be suffering from an anxiety disorder.

Understanding the genetic basis of fear could therefore help future researchers develop treatment for conditions like phobias and anxiety states, Hettema said.

Tags: health, cloning-and-dna, neuroscience