The Scientist Who Scans Fathers' Brains: The Parenting Checklist You NEED Before You Have Babies!
In a Nutshell
Dr. Saxbe's research shows fathers' brains lose gray matter—especially in mentalizing networks—when they become hands-on parents, and this shrinkage actually boosts efficiency and empathy rather than indicating loss. Men experience a ~25% testosterone drop proportional to caregiving time, and both partners' relationship satisfaction typically declines around birth unless communication is proactively strengthened. The core message is that fatherhood transforms the male brain and hormones to support investment in children, but couples must deliberately prepare their relationship, divide tasks explicitly, and build support networks before birth to navigate the transition successfully.
These notes were generated by AI and may contain inaccuracies.
Dr. Darby Saxby discovered that fathers' brains lose gray matter volume, with the most significant shrinkage occurring in the mentalizing network that helps understand others' feelings and intentions. These areas are concentrated around the midline of the cortex. Volume reduction also occurs in visual areas at the back of the brain, which are important for interpreting infant facial expressions. In mothers, changes occur across more of the brain including the subcortex, which controls gut feelings and reward, while fathers' changes are mostly in the cortex controlling higher-order thinking, reasoning, and executive functioning.
This pattern suggests that fatherhood is a cognitively mediated investment. Mothers experience hormonal flooding after pregnancy, creating high investment in infant survival. Fathers show more cross-cultural variability in their involvement, with some cultures encouraging hands-on care from birth and others prohibiting men from picking up babies. Fathers calibrate their investment based on cultural expectations and context.
Volume reduction is not a deficit but indicates the brain is working more efficiently by building better connected pathways. The brain is reshaping to enable more efficient communication, learning, and consolidating information. This allows parents to focus more energy on what matters, which becomes their children and the inputs they're giving.
The shrinkage in mentalizing networks actually improves empathy because fathers become more efficient processors of social information. The brain is building a superhighway for social information processing rather than losing capability.
Dads who reported feeling more bonded to their unborn baby before birth, wanted more time off work, enjoyed their babies more at three months, felt more connected, and spent more time caregiving showed more profound brain shrinkage. This supports the adaptive nature of the shrinkage in enabling men's adjustment to parenthood.
Men typically show about a 25% drop in testosterone when they become hands-on fathers. Longitudinal studies in the Philippines showed that testosterone is high before pregnancy, which is adaptive for competing and building status. After causing a pregnancy, men who spend more time caregiving show sharper testosterone drops. This pattern occurs across the animal kingdom.
Testosterone can drop during pregnancy due to proximity to a pregnant partner. Expectant dads and moms had correlated testosterone levels, with stronger correlations predicting greater post-birth drops.
Masculinity is not about a particular hormone level but about a body that responds to goals and meets environmental demands. High testosterone decreases sperm count and harms the immune system. The relationship between testosterone and muscle mass, motivation, and drive shows weak correlations rather than direct causation.
Men with higher testosterone after birth had partners who reported more relationship dissatisfaction and intimate partner aggression, plus the dads reported more parenting stress. Men with very low testosterone showed higher postpartum depression symptoms. The most successful fathers had mid-range testosterone levels that could adapt flexibly to different life changes.
Testosterone rebounds after birth rather than remaining permanently low. Men who spent more time changing babies, doing hands-on care, and sharing sleeping surfaces showed greater testosterone drops. There is no clear optimal dose of parenting involvement for ideal testosterone levels. Protecting sleep, getting exercise, socializing, and participating in joyful activities are recommended over trying to optimize hormone levels.
Fathers experience profound shifts in values and priorities, placing children above material goals. Men are equally likely as women to identify their kids as their most meaningful priority. The parenting role becomes central to fathers' self-concept. The biological and hormonal changes serve the larger goal of building a more meaningful life.
Longevity studies show that relationship quality is the best predictor of well-being in old age. Men with healthy marriages and positive relationships with their children age well, not necessarily those who maximized wealth or physical fitness.
The downsides of parenting are highly visible, such as crying children on planes and public tantrums. The upsides are invisible, including the joy of watching children discover new things and the sense of closeness and love bigger than oneself. Parenting provides an opportunity for connection and care on a scale difficult to find elsewhere.
Mothers lose approximately 2.5% of brain volume from before pregnancy to after birth, compared to fathers' 1% loss. The pattern is similar but the magnitude is greater in mothers with more variability among fathers.
First-time parent couples were recruited during pregnancy, with requirements for cohabitation before and after birth. Participants provided blood, saliva, and hair samples, engaged in recorded conflict discussions, and underwent brain scans during pregnancy and six months after birth. Breast milk and baby stool samples were also collected postpartum.
Couples who fought more negatively reported more difficult birth experiences. Since birth requires significant partner support, toxic relationship dynamics can negatively impact mothers' birth experiences.
When couples fought more negatively and less positively during pregnancy, specifically around six months into pregnancy, they had more medically complex births a few months later. These couples also appraised the births as more stressful. The research examined hospital charts and birth center records after delivery, looking at complications and medical complexity.
Historically, men were excluded from the birthing room, with babies typically delivered by female midwives and female relatives. It was not until the late 19th century when birth moved into hospitals that male physicians began presiding over births. It was not until the 1960s and 1970s that fathers began advocating for inclusion in the birth room.
The advice is not to avoid fighting during pregnancy, but rather to find more effective ways to fight. The goal is to calm each other down and validate each other rather than amp each other up and get into negative spirals.
Negative conflict behaviors that were specifically studied include criticizing, showing contempt, and stonewalling, which involves refusing to listen or see the other person's perspective. Validation was identified as a key ingredient that helps couples shift from negative to positive interactions during conflict tasks. Conveying to a partner "I understand what you're saying, I see where you're coming from, I'm right here with you, I get it" makes a significant difference by reducing tension and frustration.
There is no right time to have children. The recommendation is to simply do it and make it work, because once the baby shows up, parents will figure it out. This advice led to having children within a few years after receiving it.
Optimizing everything and waiting for perfect conditions such as owning a house with a specific number of bedrooms or achieving a certain level of stability can delay having children indefinitely. Historically, people had children young and often found that having kids provided strong impetus to get their lives together. The cultural shift has moved from viewing having children as a cornerstone of life, where you build your career and other aspects around family, to viewing it as a capstone, where everything must be perfectly set before having children.
The global fertility rate has plummeted from an average of five children per woman in 1950 to just 2.2 today. The US total fertility rate hit an all-time recorded low of 1.6, far below the replacement rate of 2.1 children per couple required to keep the population stable without immigration. US birth rates dropped by 1% in 2025, falling to roughly 3.6 million babies, continuing a nearly two-decade decline since the Great Recession.
A landmark 2024 study published in The Lancet projects that by 2100, 97% of all countries and territories will have fertility rates too low to sustain their populations. Due to fertility rates crashing in high-income nations while remaining high in specific low-income regions, a massive shift in human demographics is predicted, with one in every two children born on the planet expected to be born in sub-Saharan Africa by 2100.
An inverse age curve, where there are many more old people than young people, creates problems including insufficient caregivers for older populations, inability to sustain the economy, and lack of innovators to build the future.
A cultural reframe around care is needed to raise the value of care. Seeing men as talented caregivers unlocks appreciation for the importance of care. The shift from a transactional focus on making money to prioritizing time with children represents a valuable change in purpose that would make societies healthier and more empathetic at scale.
Research from the UK Biobank, the largest repository of brain scans from people in their 50s and 60s, found that both men and women who reported having more children have markers of a younger looking brain age. A machine learning algorithm adjusted for chronological age and estimated brain age from scans, revealing that parents appear relatively younger. The greatest benefit appears to be at two or three children, after which the benefit levels off.
Parents of young children report being less happy moment to moment, more tired, and more stressed. However, in later life, people report more fulfillment from parenting. The practice of parenting provides a workout for social cognition, similar to Sudoku for understanding people's minds and intentions, communicating, responding, and being sensitive to others. This is also a full-body workout because children are embodied.
Fathers engage in physically demanding, vigorous play with children, including proprioceptive touch such as picking babies up, moving them around, and playing with them. Dads who engaged in more of this type of touch subsequently had higher oxytocin levels in blood draws.
Oxytocin actively downregulates harmful pro-inflammatory cytokines in the brain and acts on the brain's immune cells, making toxic inflammatory responses lower. Studies on aging mice demonstrated that long-term oxytocin treatment enhanced the brain's plasticity, which improved learning and memory as they aged. In animal models of Alzheimer's, oxytocin reduced the toxicity of amyloid beta plaques, the toxic protein clumps that are the hallmark of Alzheimer's disease.
The model of a single parent with a single child isolated in a suburban home is unusual in the context of human history. Humans are designed to collectively raise children and share care. The idea that children cannot do well in group care settings is considered exaggerated. Very young babies often do better with a single caregiver for stable attachment, but babies can form strong attachments with fathers and other caregivers. Ideally, group care becomes beneficial around 18 months and beyond when children can benefit from social interaction.
Universal paid parental leave, which is not available for most parents in the United States, would support parents who want to avoid early childcare. Parenting stress is considered bad for children, making sustainable approaches that allow parents to get help important.
Dads should be able to access paternity leave up to their child's 18th birthday because the strongest father-child relationships often develop later in childhood or during adolescence. Examples include taking kids on trips and teaching sons how to drive. Dads can provide significant value at different developmental stages. Early in infancy, breastfeeding creates a biological head start for mothers, which can leave dads feeling uncertain about their role. While mothers can pump and dads can bottle-feed, this dynamic frequently creates challenges in the first year or two of parenthood. Dads often need space and opportunity to figure out their parenting approach independently rather than waiting for instructions from mothers who become the default parent.
Maternal gatekeeping refers to any time a mother consciously or unconsciously creates barriers to fathers' full participation in parenting. This can manifest as simple actions like taking a fussy baby from the father with comments like "Hand him to me. I know what to do." Over time, this pattern positions mothers as the authority figure while fathers appear incompetent. Dads may feel their contributions aren't valued and that mothers don't trust them with independent time with the child. Trust and communication before birth become critical to preventing this dynamic.
The flip side is weaponized incompetence or husbandly malingering, where competent men who manage complex work responsibilities suddenly claim inability to handle basic parenting tasks like packing a diaper bag. One example involved a father calling his wife during a diaper blowout just two days after birth, asking what to do despite the mother having the same amount of experience. Another case involved a father questioning whether children could eat anything besides chicken nuggets when asked to pack lunches.
Transition to parenthood research consistently shows a statistically significant drop in couple relationship satisfaction around the birth of a new baby. This occurs due to sleep deprivation, increased responsibilities, and conflict over task division. Couples who anticipate this risk can strengthen their communication before the baby arrives. Some couples experience continued decline leading to relationship dissolution, while others report improved relationship quality after parenting together, often citing deeper appreciation for their partner.
Postpartum depression refers to depression occurring after a baby's birth, regardless of which parent experiences it. New fathers have approximately twice the depression risk compared to non-fathering men, though rates remain lower than for new mothers. Risk factors include hormone changes, sleep disruption, identity shifts, relationship conflicts, work changes, extended family dynamics, and reawakened childhood traumas. The term "perinatal depression" has been suggested as a more inclusive alternative that encompasses the period around birth for both parents.
Research on cortisol interconnection between couples found that strongly linked cortisol levels correlated with lower marital satisfaction. Rather than being beneficial, stress hormone synchrony may indicate problematic stress contagion between partners. The ability to modulate and calm a stressed partner appears more beneficial than matching their stress state. However, other research suggests cortisol synchrony may be beneficial specifically during the transition from pregnancy to postpartum.
Humans uniquely conceal ovulation, unlike other animals with obvious fertility cues. This concealment encourages pair bonding because men cannot simply identify and pursue fertile periods before departing. Concealed ovulation promotes stable monogamous relationships, reduces aggression between women by eliminating visible fertility competition, and creates broader community investment in children since paternity remains uncertain.
Great fathers are made, not born. The transition requires time, investment, practice, and genuine care rather than innate qualities. New fathers should give themselves grace during the challenging transition period while recognizing they can become experts in their own child. The process ultimately brings enrichment, meaning, and rediscovered priorities.
Studies using "who does what" questionnaires given before and after birth revealed that every couple expected fathers to do more childcare than they actually performed after birth. Fathers who did more childcare reported greater relationship satisfaction. Additionally, fathers who used more "we" language when discussing baby care division showed higher relationship satisfaction after birth, controlling for pre-birth relationship feelings.
Before birth, couples should have explicit conversations about dividing baby care responsibilities rather than planning to "wing it." This includes discussing extended family involvement, religious upbringing, and educational values to prevent later conflicts. Building social support networks before birth provides crucial buffers against depression, as new fathers often find their primary confidant (their partner) preoccupied with the baby. This includes identifying how family members and friends can provide specific types of support, and building community with other expectant parents and neighbors.
Mothers typically have more organic community-building opportunities like breastfeeding support groups and mothers' clubs, while fathers often lack equivalent structures. Taking advantage of available community resources becomes essential for building the support network needed during the transition to parenthood.
The Daddy Stroller Social Club has chapters across the country where fathers meet for stroller walks with their children, providing an effective way for dads to connect with each other. Building these support networks should be prioritized before having children.
Three key areas to focus on before the baby arrives include building friendships, strengthening the couple relationship, and planning how to balance responsibilities once the baby comes. Sleep preparation is critical - establishing healthy sleep routines and good sleep hygiene before birth helps parents fare better after the baby arrives. This includes avoiding devices before bedtime, dimming lights, and maintaining optimal room temperature.
The sleep deprivation that comes with new parenthood creates a vicious cycle where stressed or sleep-deprived individuals often reach for dopamine-rich foods. Preparing for parenthood should be approached like training for a marathon - focusing on overall health to prepare the body for this major life change.
Fathers should embrace baby care opportunities like diaper changing as chances to make eye contact and bond with their baby. Finding personal parenting styles and maximizing bonding windows leads to greater confidence and connection with the child. Parents should give themselves grace, recognizing that the difficulties are temporary and the short-term sacrifices lead to long-term benefits.
Strengthening the couple relationship before the baby arrives involves improving communication and having difficult conversations. Date nights often disappear after the baby comes, but newborns can sleep anywhere, allowing couples to take advantage of this portability. Parents can bring babies in car seats to restaurants and continue some activities that become impossible once children start walking.
The concept of giving yourself grace applies differently to mothers and fathers. Women experience matrescence - a complete transformation of their sense of self and priorities when becoming a parent. Both partners undergo significant changes, and understanding these transformations helps couples support each other through the adjustment period. Common conflict areas include dads feeling jealous of attention given to the baby, and moms feeling frustrated when dads aren't helping enough.
Research across both animal and human studies shows males tend to gain weight when becoming fathers. This results from multiple factors including rising prolactin levels, sleep deprivation, reduced physical activity, and dietary changes due to stress. A study of tamarin monkeys found that expectant fathers gained more weight than non-expectant males even when fed identical diets, suggesting these body changes may be adaptive for increasing physical presence and storing reserves.
Studies of single women show that dadbods are the most preferred male body type when shown various options. The appeal appears linked to perceptions that men with dadbods are more likely to be hands-on, attentive, and caring fathers - qualities that women find attractive.
Dr. Saxbe's parents divorced when she was nine, after which her father became a solo parent to her and her brothers through a joint custody arrangement. This experience influenced her interest in families and couples, and seeing her father develop into an excellent caregiver highlighted the gap in parenting research that focuses primarily on mothers.
Humans can be described as "monogamous with benefits" based on body size differences between males and females. Unlike gorillas with extreme size differentials indicating harem dominance, or prairie voles with virtually no size difference indicating strict pair bonding, humans fall somewhere between these extremes. Monogamy is the most common relationship model across cultures and societies, partly because concealed ovulation encourages male investment in single partners, and partly because it benefits children.
Declining birth rates signal concerning trends about young people's hopefulness for the future. Marriage rates are dropping, and young men and women appear to be on different paths partly due to algorithmic echo chambers creating different content consumption patterns. This contributes to increasing political polarization and adversarial interactions across societies.
Despite concerns, there is optimism for future generations, particularly teenagers who may bring greater wisdom to addressing current challenges. Building strong relationships remains a key predictor of healthy aging and longevity.
The United States lacks a universal paid parental leave policy at the federal level, making it an outlier compared to other countries. Some states offer unpaid disability leave, but this isn't available to all workers including shift workers, gig workers, and many retail employees. The Family Medical Leave Act provides up to 12 weeks of unpaid leave with job protection and continued health insurance, but this creates financial hardship for many families.
Paid parental leave enjoys approximately 80% public support across both political parties, yet lacks the political will for implementation. Better policy environments around parenting, including protected bonding time through parental leave, would benefit American families significantly.
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