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.
AKC PuppyFinder: American Staffordshire Terrier Puppies. Personality: AmStaffs of proper temperament are smart, confident, good-natured companions; their courage is proverbial. Energy Level: Somewhat Active; Versatile and athletic, AmStaffs like mental and physical challenges. Good with Children: Better with Supervision.