“Whereas mothers are biologically prepared to nurture, teach, and provide care that is especially important for foundational development, fathers are predisposed to take a facilitative approach to parenting, fostering self-reliance, achievement, and healthy peer relationships in ways that are particularly important especially as children begin to transition to adult life.”

As the Supreme Court considers whether to redefine marriage in genderless terms, scholars supporting gender-diverse parenting filed an amicus brief urging the Court not to eviscerate this fundamental norm of marriage given its crucial benefits to the development of children. If same-sex marriage is constitutionalized, the message the law will send is that the gender of parents becomes valueless, since any two adults will do.

Gender Diversity Is in Our Genes

In the late 1970s, Azim Surani tried to create new life using two sets of genes from only a mother, or a father. Everything then known about genetics suggested that with the right number of chromosomes, life would develop normally, even if all of its genetic material came only from a female or a male. But the eggs with only the mother’s genes could not survive. A similar fate met the eggs implanted with two sets of father’s genes.

As science reporter Paul Raeburn describes, Surani discovered that mothers and fathers each contributed something in their genes that was critical to sustaining life. These “paternal” and “maternal” genes appeared completely indistinguishable in every way, yet expressed themselves differently depending on whether they came from the mother or the father. And both were essential to the survival of the egg.

The essential need for both a mother and a father to provide genetic material for survival parallels what social science tells us about the importance of mothers and fathers in children’s development. Fathers and mothers bring similar, even indistinguishable, capacities that enable healthy child development. But like the complementarity of the left and right halves of the brain, they also bring distinct capacities that provide complementary, irreplaceable contributions to children’s healthy development.

Coo and Cuddle vs. Tickle and Toss

Consider what social science research reveals about how mothers and fathers distinctively influence children’s social and emotional development. Mothers are biologically primed to provide nurturing oriented toward creating a strong attachment relationship. Dramatic increases in oxytocin and oxytocin receptors during the process of giving birth and caring for infants act like a switch in mothers, turning on maternal behaviors. New moms find themselves expressing positive feelings, affectionately touching and gazing at their infants, and engaging in “motherese” vocalizations. Infants’ levels of oxytocin parallel their mothers’, producing feelings of calm and well-being that similarly bond mother and offspring.

Fathers also experience significant physiological changes that “prime” them for bonding. But the same hormones elicit different types of responses. Instead of inviting “security-inducing” behaviors, fathers’ levels of oxytocin are associated with “stimulatory” behaviors, like tickling and bouncing. This suggests a biological foundation for what we observe all around us. While mothers are more likely to “coo and cuddle” their infants, fathers are more likely to “tickle and toss.” These differences foreshadow more extensive complementary patterns exhibited across children’s development.

Identity and Emotional Capacity vs. Social and Relational Capacity

A mother’s capacities are uniquely oriented toward identity formation and emotional security. Her ability to detect, interpret and respond in positive, non-intrusive ways to her infant’s needs has been identified as the strongest and most consistent predictor of a child’s social, emotional, and cognitive development. Neuropsychological studies indicate that mothers have a uniquely sensitive ability to modify the stimulation they give to their infants, matching their infants’ inner state and providing the optimal “chunked bits” of positive interaction needed for development. In the process, children experience positive effects on memory, cognition, stress tolerance, and emotional and behavioral regulation, as well as cardiovascular, metabolic, and immune function.

In this secure attachment relationship, children develop their own sense of identity while learning to appreciate, understand, and empathize with the feelings of others. From infancy on, children are more likely to seek out their mothers for comfort in times of stress. And mothers are much more likely to identify, ask about, listen to, and discuss emotions with children. A mother’s unique orientation toward identifying, expressing, regulating, understanding, and processing emotions is not only important for self-awareness and emotional well-being; it also lays a foundation for moral awareness, including a sense of moral conscience with the capacity to distinguish between right and wrong.

Fathers demonstrate a complementary influence. While mothers are uniquely important in developing secure identity and emotional understanding, fathers are uniquely important in developing social and relational capacity. Interestingly, this complementarity is reflected in the way mothers and fathers hold their infants. While a mother is likely to hold her infant to enable maximum contact with her face and body, a father is most likely to hold the infant in a way that gives the baby the same view of the world as the father has. This “football hold” orients the infant’s face outward, toward others.

It is fathers’ involvement with their children that consistently predicts how they relate to others. Father closeness during a child’s adolescence has been identified as the key predictor of empathy in adulthood, as well as marital relationship quality and extra-marital relationship quality in adulthood. In contrast, lack of father involvement has repeatedly been associated with delinquent and criminal behaviors, even into adulthood. For boys, the mere presence of a father in the home predicts less delinquent behavior.

Some of this may be due, in part to the discipline style of fathers. Fathers intervene to discipline less often than mothers, but when they do, they exhibit more firmness and predictability. In contrast, mothers use more reasoning and flexibility in carrying out consequences. Children, in turn, are more likely to comply with their father’s requests and demands than with their mother’s.

More significantly, fathers influence children’s social and relational capacity through their play. Compared to mothers, fathers are much more likely to interact through play. And that play is strongly predictive of the quality of children’s peer relationships. In repeated studies, fathers who spent more time in positive play with their children had children with the highest peer ratings. When fathers were more responsive, patient, playful and less coercive in their play, children showed less aggressiveness and more peer competence, and they were better liked.

As one report noted, “Rough-housing with dad” appears to “teach children how to deal with aggressive impulses and physical contact without losing control of their emotions.” Through play, fathers help children learn how to temper and channel emotions in a positive, interactive way and gain confidence in their ability to do so. As children age, fathers focus less on physical play and engage in more peer-like verbal play in the form of sarcasm and humor. Peer-like verbal play allows a father to tease and joke with a child, within the safety of the father-child relationship, thus strengthening children’s sense of identity and social confidence. While mothers consistently build self-understanding, fathers consistently build social-relational understanding.

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