Genetic and hormonal influences on affiliative behavior in humans

Sammanfattning: Affiliative bonds between romantic partners are widespread pan-culturally and an important part of human nature and society. Still, knowledge about the biological correlates of human pair bonds is sparse. Studies in rodents, voles in particular, have shown the neural circuits involving vasopressin and oxytocin, in males and females respectively, to be very important in the formation and regulation of pair-bonding behaviour. Further, both neurobiological and evolutionary studies have shown mate guarding behaviour to be closely linked to pair bonding. In this thesis data from several twin samples from Sweden as well as from a randomized experimental study was used to investigate genetic and hormonal influences on pair-bonding behaviour and jealousy. Primarily, factors related to vasopressin and oxytocin were investigated. Variation in the vasopressin receptor 1a gene and the oxytocin receptor gene was shown to be associated with pair-bonding behaviour in men and women, respectively. Further, intranasally administered oxytocin was shown to influence pair-bonding related behaviour in women. Finally, in accordance with evolutionary theory, men and women scored differently on quantitatively assessed jealousy. This difference was not detected on a genetic level. Genetic modeling analyses did however reveal that about 30% of the variance in jealousy is explained by genetic factors in both men and women. Taken together, these results suggest that the well characterized effect of vasopressin and oxytocin on pair bonding in voles may be of relevance for humans. Also, the results from the quantitative genetics analyses, showing that genes are of importance for jealousy, make it interesting to hypothesize that the genes associated with pair bonding could influence jealousy as well.