Biopsychology of Transition to Fatherhood

The focus of this work was on fathers across the transition to fatherhood. The purpose of the empirical studies was to explore the association of testosterone (T) and paternal investment including interpersonal differences in personality traits and relationship quality. Providing paternal care is associated with a reduced likelihood of engaging in competitive or mating behavior and also of providing protection when necessary. T is a psychobiological marker of reproductive behavior. Recent studies found decreasing T levels in males across the transition to fatherhood, in order to reduce mating effort in favor of providing paternal care. In addition, there is empirical evidence for reducing relationship quality in parents across the transition to parenthood. Therefore, a direct association of T level and relationship quality was suggested. Moreover, researchers have assumed that sensation seeking (SS) is associated with both mating effort and T. For this reason, the personality trait SS was included in further investigations of the second study of this work. Thirty-seven fathers and 38 men in committed romantic relationships without children (controls) were recruited. On two days (four weeks prior to (t1) and eight weeks after birth (t2) for fathers, and three months after the first measurement day for controls), all subjects repeatedly collected saliva samples for T measurement at three times of the day, filled in a protocol of activities and completed online questionnaires. In the two empirical studies presented in this work, the following main results were obtained: In line with recent studies, fathers showed significantly lower T levels (AUCg-T) than controls at t2; moreover, fathers showed a significant decrease in relationship quality, whereas relationship quality of controls did not change significantly over time. In particular, the values of the subscale Tenderness decreased significantly in fathers from t1 to t2. Furthermore, the T level at t1 interacted with the change in T level from t1 to t2. This interaction was associated with the extent of decrease in Tenderness during the transition to fatherhood. Since Tenderness, including sexuality, might reflect aspects of mating effort, these results corroborate the "challenge hypothesisż in humans, whereby T level is positively associated with mating effort and negatively related to paternal activities. In the second study, linear regression revealed a significant interaction between group and SS, meaning that SS moderates T levels across the transition to fatherhood. Fathers with low SS showed a significant change in the diurnal fluctuation of T from t1 to t2, whereas the diurnal fluctuation of T in fathers with high SS did not change significantly. In conclusion, the transition to fatherhood is associated with a reduction in the extent of diurnal fluctuation of T for fathers with low scores in SS.Given the inconsistencies in empirical evidence in research on the transition to fatherhood and the potential importance for understanding paternal behavior, with its correlates of endocrinological aspects, the studies of this work are the first to combine psychological and endocrinological aspects in a longitudinal design and to compare potential changes and associations with a matched sample of men without any children as controls.