It has been empirically supported that brain chemicals and outside substances have an influence on sperm and egg cells, thus subsequently, the embryos and children that those gametes eventually produce.  A scientist in Mexico recently proposed that endorphins and thus happiness may be one of the brain chemicals that plays a role in determining the genetic make up of gametes.  This is in addition to and aside from existing genetic make up affecting temperament.

Elsevier (2009, May 14). Can Happiness Be Inherited?. ScienceDaily. Retrieved May 14, 2009, from­ /releases/2009/05/090514101937.htm