Psychologists, quality of life and well-being researchers have grown 
increasingly interested in understanding the factors that are associated with 
human happiness. Although twin studies estimate that genetic factors account for 
35-50% of the variance in human happiness, knowledge of specific genes is 
limited. However, recent advances in molecular genetics can now provide a window 
into neurobiological markers of human happiness. This investigation examines 
association between happiness and monoamine oxidase A (MAOA) genotype. Data were 
drawn from a longitudinal study of a population-based cohort, followed for three 
decades. In women, low expression of MAOA (MAOA-L) was related significantly to 
greater happiness (0.261 SD increase with one L-allele, 0.522 SD with two 
L-alleles, P=0.002) after adjusting for the potential effects of age, education, 
household income, marital status, employment status, mental disorder, physical 
health, relationship quality, religiosity, abuse history, recent negative life 
events and self-esteem use in linear regression models. In contrast, no such 
association was found in men. This new finding may help explain the gender 
difference on happiness and provide a link between MAOA and human happiness.