How someone falls in love -- love at first sight or friendship that turns to romance -- and the style in which a relationship is pursued has little to do with one's genes, say the authors of a UC Davis study. The study, based on nearly 900 adult twins from the California Twin Registry and more than 170 spouses, is to be published in a forthcoming issue of "Psychological Science" and is the first such behavior-genetic study of romantic love. A common family environment, not heredity, appears to play a substantial role in determining love styles, say Niels Waller and Phil Shaver, UC Davis psychology professors and co-authors of the study. The finding, they say, fits with theories that stress the importance of family interactions in personality development. Waller and Shaver conclude that love styles, but not most other personality traits, are due more to shared environments than genetics because they are inherently relational. "Unlike simple emotions and individual personality traits which are related to heritable variation . . . love styles may be learned during early familial interactions and subsequently played out in romantic relationships," conclude Waller and Shaver.