A study from Northwestern University and the University of California reveals the so-called "happy hormone," serotonin, influences long-term relationships.
One hundred fifty couples were tracked for 20 years.
Those with the specific genes linked to positive emotions thrived in marriages with humor and affection and withered with conflict.
A separate genetic makeup found partners far less bothered by the emotions.
The research showed those whose DNA made them less sensitive to the ups and downs of relationships actually had happier marriages.