A person's disposition toward happiness or misery is genetic, scientists have proved during the past two decades.

As much as one-third of the difference in people's happiness levels is passed on through DNA, according to a report jointly compiled by scientists from University College, London, Harvard Medical School, the University of California, San Diego, and the University of Zurich. They examined more than 1,000 pairs of adolescent US twins in a study published in the Journal of Neuroscience, Psychology and Economics in 2011.

The chemical contributors to happiness are mainly serotonin and dopamine, which are neurotransmitters secreted by cells. Their levels are determined by a person's DNA. The higher the levels of these chemicals, the happier a person is.