Sunny Side of the Street

I have often wondered if optimists were born that way or if their life experiences served to mold their positive dispositions.  Is there a happiness gene that some people get in utero that enables them to have a sunny outlook as they develop or does a life filled with plenty of positive experiences lay the foundation for lifelong optimism?  More importantly, and perhaps even more relevant to my question,  would those born with the 'gene of optimism' maintain their positive outlooks if their lives took a turn and more adversity started heading their way?  I wonder...