Research indicates that generalized anxiety disorder is more common than specific phobia. phobic reactions to cats are much more common than to dogs. people, but not animals, may acquire fear through observational learning. some people are more genetically predisposed than others to develop anxiety disorders, ocd, and ptsd.

Phobias are extreme fears that make it impossible to function normally. Phobias may grow out of really negative experiences, but because they are overwhelming and often irrational, they become disabling. There are many different types of phobias; some of the most common include:

Fear of specific animals (dogs, spiders, etc.)

Fear of open spaces, enclosed space, or high places

Fear of natural events, such as thunderstorms

While fears are an unavoidable part of being human, most fears can be controlled and managed. Phobias, however, cause psychological and physical reactions that are difficult if not impossible to manage. As a result, people with phobias will go to great lengths to avoid the object of their fears.

More research will need to be performed in order to isolate the complex genetics involved in the development of phobias and other anxiety disorders. However, this study does support the theory that genetics play a major role.

the answer to your question is,

old stone age.

-mabel < 3