It is well known that in humans, as in other species, fathers and mothers show different parenting behaviors toward their children. Mothers generally tend to establish facial and affectionate interactions, conveying a sense of security to children, while fathers interact in a more playful way, preparing the child for novelty and excitement. These two different types of interaction are essential for the development of the baby's personality and sociability (see «Some Psychological Aspects of Fatherhood»).
Scientific evidence indicates that these maternal and paternal behaviors are regulated by neuroendocrine circuits, and it has indeed been shown that hormones play a significant role in how parental care toward the newborn is expressed.
While the influence of pregnancy and birth-related hormones on maternal behavior is a widely studied topic, little is known about the neuroendocrine mechanisms underlying paternal behavior. Data reported in the literature to date suggest that three main hormones are involved in shaping a father's behavior toward his newborn: oxytocin, prolactin, and testosterone.
Oxytocin
Oxytocin is a hormone produced by the hypothalamus and secreted by the posterior pituitary gland. Although oxytocin is typically considered a maternal hormone associated with birth and breastfeeding, scientific studies show that this hormone is associated with the bonding of both parents to their children. In fact, maternal oxytocin is responsible for the mother's affectionate behavior toward the child, while paternal oxytocin is responsible for the more stimulating interaction between father and child.
Prolactin
Prolactin, a hormone produced by the anterior pituitary gland, is well known for its role in milk production and in the mother's behavior during breastfeeding. However, since scientific evidence also supports its role in the emergence of paternal behaviors, scientists have named it «the parenting hormone». The results of studies conducted in this area show that prolactin levels influence fathers' ability to form affectionate bonds with their children. Indeed, fathers who are more attentive to their child show higher prolactin levels than men who are not fathers or who are less responsive to their children.
Testosterone
Testosterone is a hormone produced mainly by the testicles. Its synthesis and production are influenced by luteinizing hormone (LH), produced by the pituitary gland. The female ovaries also produce this hormone, but in much smaller amounts than the male gonads. In men, testosterone plays a key role in the development of male reproductive tissues (testicles and prostate) and promotes secondary sexual characteristics (increased muscle and bone mass, body hair growth). Over the past decade, many studies have looked into the role played by testosterone in fatherhood. In particular, it has been shown that men who become fathers experience a decrease in testosterone levels, and that men who provide more paternal care to their children have lower testosterone levels than less attentive fathers.
It is interesting to note that the rise in prolactin and the drop in testosterone after the baby is born not only shape paternal behavior toward the infant but can also reduce libido. The biological significance of this change lies in the fact that a reduction in the parents' sexual behavior leads to greater involvement in caring for the baby. In this regard, a 30-year longitudinal study found that adequate parental presence during a child's early years leads to better sociability and better emotional balance in adulthood.
Based on the scientific findings available in the literature, the importance of the hypothalamic-pituitary-gonadal axis becomes clear as a mediator of the trade-off between becoming a parent and mating for its own sake, as has also been observed in other species (rodents and birds) in which paternal care is common.