This may be a harsh reality for some to accept, but just as a 'depressive brain' can be inherited, there is a strong relationship between happiness and genes (or the happy brain, if you will). Happiness is 50% heritable. There is a genetic set point that each person has inherited and although people may fluctuate from that set point, based on negative experiences that they may encounter, they will come back to that level of happiness that they were genetically predisposed to having.