It's not just serotonin either-most neurotransmitters can cause anxiety or anxiety like symptoms, and in some cases an over-abundance of a chemical can lead to anxiety. So it does appear that you can develop it without experiencing a stressful life.
Howard Heinzl (1918 - 1989) With regard to blue American Staffordshire Terriers, any breeder that believes that a blue American Staffordshire Terrier is some how more valuable than the other recognized colours, is not only deceiving themselves, but they are also deceiving their customers.
1 For New Owners: Both the Neapolitan Mastiff and Staffordshire Bull Terrier are better suited for owners with previous dog ownership experience.  With Kids: The Staffordshire Bull Terrier is better for kids. It can grow up with them and become a great family pet.