Mice lacking functional nerve cell receptors for this neurotransmitter, gamma-amino butyric acid, are more fearful than mice having the receptor. Fear which in humans ranges from generalized anxiety to specific phobias is an important biological adaptation and a common behavior in all mammals. Fear is an emotion, an unspoken memory, stored in special parts of the brain. It provokes individuals to react rapidly, almost instinctively, in the face of perceived danger.
Fear can be present in greater or lesser degrees in different individuals.
When a tendency to fear is present in excess, its consequences are not always helpful. As many as one fourth of all Americans will suffer from potentially debilitating anxiety , panic disorders , animal phobias and post-traumatic stress reactions at least once in their lives. These disorders cause not only mental anguish but a variety of real physical symptoms, including localized pain. As with other forms of behavior, we would like to know to what extent fear is learned from environmental experience and to what extent it is influenced by our genetic makeup. The study of fear in animals such as mice has shown that fear can be selectively bred into succeeding generations, suggesting a strong genetic component.