The majority of our understanding of human personality has concluded that we are born with blank slates that are filled with our experiences.  This line of thought prevailed for much of the 20th Century, with only recent advances in our neurological understanding suggesting that in fact our personalities are derived as much from our genetics as they are from our circumstances.

Happiness is central to our notion of personality and recent studies have suggested that happiness is significantly more genetically determined than previously thought.

A study was conducted of 1,000 pairs of twins to determine how much of our happiness is hereditary.  This research found that around 1/3 of our happiness can be pinned to genetics.

A break out from this research was conducted in order to try and understand which genes in particular are responsible for our happiness.  The Serotinin-Transporter gene was tested to gauge the impact of the two variants of this gene on happiness.  The research found that if a person had 1 long version of the gene and 1 short, they were 8% happier than those with 2 short versions of the gene.  If an individual had 2 long versions however they were 17% happier.

All very interesting.  The research also asked participants to describe their ethnicity.  Asian participants on average had just 0.69 long genes, white participants had 1.12 and black participants had 1.47.  So this would suggest that Asians 'should' on average be unhappier than African Americans.

Some research does support this, with Asians reporting lower levels of happiness than their GDP suggests.  

Of course nurture factors are important too.  For instance extroverts are shown to be happier than introverts, middle aged people are found to be glummer than the young and old, employment affects our happiness and so on.  But this research shows that there is perhaps more to happiness than meets the eye.