Expecting and fathering a baby radically changes a man's brain too.
We know a lot about the body and mind changes for expectant and new mothers. Previously, men may have felt left out, not sure how to account for their own unfamiliar feelings before and after the arrival of a baby. Now, studies show that expecting and fathering a baby radically changes a man's brain, too.
It's as if nature has a plan here!
Right after hearing the news that he's about to be a father, a man starts to produce cortisol, a stress hormone. Cortisol levels tend to spike around 4 to 6 weeks after hearing the news, and then decrease as his mate's pregnancy progresses. Then, about three weeks before the baby arrives, his testosterone levels fall by about 30%, making him more cooperative, less competitive, and more likely to show his softer side.
Also during the last few weeks of his wife's pregnancy, researchers say that a man's prolactin level rises by 20 percent. It's not totally clear what effect prolactin has in a man, but it is thought to have an indirect impact on those falling testosterone levels. After his child's birth, his estrogen level, a nurturing influence which is normally very low in a man, increases. The point of these changes is to make fathers more maternal in their behaviors, more than their normally high levels of testosterone will allow. About 6 weeks after birth, his hormone levels begin to return to normal.
Birds "Do It"
Experiments carried out with several species of monogamous birds found that those male birds with higher testosterone levels tended to be absentee fathers who went off for a polygamous turn while the mother bird tended her nest of hatchlings. In men, higher testosterone has also been shown to increase infidelity and decrease nurturing skills. Fortunately, most male birds and human males are more willing to settle into domesticity during the early days and months of infant care.
What else Happens to New (human) Dads?
With lower testosterone, their sex drive drops, too. Some researchers believe that pheromones are at work in preparing macho men to become doting dads, at least for the first few weeks. This scenario has men receiving his wife's pregnancy chemicals through his sense of smell, and then becoming more like her.
His higher estrogen, along with lots of skin contact with his baby, triggers oxytocin in a man, which helps to reinforce a father's newfound cuddling and cooing behaviors.
Daddy Play is Different than Mommy Play
You may have already noticed that fathers tend to interact with infants and toddlers in different ways than mothers. A father is more likely to jiggle or rock babies in a playful, rhythmic fashion, while women use firm or light touching to soothe and contain them. As children grow older, a father tends to take a more rough-and-tumble approach to their physical care, and be more challenging and less sympathetic than a mother. Research shows that both approaches are good and necessary for developing children.
Daddy and Mommy and New Baby
It's important for new parents to know in advance just how much this new member of the family will change their own relationship--at least temporarily. For starters, because of the new mother's hormonal changes as a result of giving birth, and then nursing her baby, a mother is quite literally "in love" with this new tiny person. Sorry, Dad, for the moment you come second. When his wife falls in love with her newborn baby, a father can feel jealous and left out. This is normal, hormonally driven behavior. It's also temporary, but husband should not be in too much of a rush to return to regular lovemaking; her libido is likely to be lower for up to a year
While she's nursing, a new mother will find she's mentally fuzzy and forgetful, again thanks to the hormones (oxytocin and prolactin) flooding her brain in great quantities. Together, this leads a new mom to have "mommy brain" where she's happy but easily distracted and unfocussed. Add in the usual lack of sleep for a good six months after a baby is born, and nothing will feel the same to the new mother or father because it isn't.
Finally, certain sexual behaviors with her partner can temporarily be dangerous to a new mother, given that her body has just undergone such a radical change. Couples should be sure to get a post-natal checkup before engaging in sexual activity.
Maternal, nurturing behavior is not strictly a new biological parent's prerogative. Older siblings, adoptive parents, grandparents, caregivers, and others will respond maternally after they experience close daily contact with an infant. Physical cues from the baby about his needs for feeding, a dry diaper, holding, or calming will literally forge new neural pathways in a caretaker's brain, just like those in a new mother. These brain changes are then reinforced by an influx of oxytocin from skin to skin contact with the baby.
For more on the science of human bonding, read The Complete Idiot's Guide to the Chemistry of Love, coauthored with Maryanne Fisher.