De neve looked at the genetic makeup of 2574 people selected to be representative of the general population , whose medical histories were recorded for the us national longitudinal study of adolescent health .
Dr de neve found that those with one long allele were 8 % more likely than those with none to describe themselves as very satisfied ; those with two long alleles were 17 % more likely .
De neve calculated that , everything else being equal , having one long version of the gene increased the number of people claiming to be " very satisfied " with life by around 8.5 % . Having two long versions raised the number by 17.3 % .