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.
An American Staffordshire Terrier may be right for you. If you don't want to deal with... Legal liabilities (public perception, future breed bans, insurance problems, increased chance of lawsuits) An extremely careful search to be sure you're acquiring a stable-tempered individual.