Neurobiology of Gender

By Robert Sylwester

Dr. Robert Sylwester is professor emeritus of education, University of Oregon. He has published numerous articles on the subject of how new developments in science and technology impact education and is the author of 20 books and curricular programs. His most recent books are A Biological Brain in a Cultural Classroom (2003) and How to Explain a Brain: An Educator’s Handbook of Brain Terms and Cognitive Processes(2005). Robert Sylwester is the recipient of honorary doctorates from three Concordias (Seward, River Forest and Portland) and continues to lecture on the topic of education and science throughout the world.

A generation ago our society experienced a contentious reexamination of the concept of race and its relationship to equality in civil rights and benefits. We are now engaged in a similarly explosive rights/benefits examination within the context of marriage – whether the civil rights and benefits that automatically accrue to heterosexual couples through marriage should be extended to bonded homosexual couples who wish to marry.

Further, our society is simultaneously confronting additional gender issues, such as the role of females and homosexuals in the ministry and military service; the value of same-sex classes in school; the appropriate focus of sex-education programs; gender patterns in criminal behavior; female aptitude in science and math; and the higher incidence of males or females who suffer from various body/brain disorders.

All these issues incorporate complex biological, theological, cultural, and political elements, and in our social species sexuality/bonding may well be the central issue. Gender has historically been defined as the separation of humans into male and female groups, with consequent cultural role and behavioral expectations.

Traditional gender perceptions and issues are now compounded by research technologies that can compare male and female body/brain structures and cognitive activity in ways not previously possible; and by such culturally confusing and controversial conditions as trans-sexuality and intersexuality (children who are born with an ambiguous sexual system that often creates issues related to gender identity and sexual orientation as they mature).

The traditional conventional wisdom that we consciously choose our sexual orientation has eroded as people thought more about their own personal experience, and about other biological predispositions (such as handedness and temperament) that they similarly didn’t consciously choose. The roles that culture and genetics play in gender behavior has similarly become problematic as parents observe developmental variations in children’s play patterns and adolescent friendship preferences.

It thus appears that individuals are either clearly male or female, or else exist (for whatever biological and/or cultural reasons) somewhere within an androgynous category that’s biologically and behaviorally separate from the two pure gender strains. Perhaps 10% of the human and non-human mammalian population falls within this category. Gender thus isn’t the simple straightforward conscious phenomenon that most folks formerly believed, and that some folks continue to believe. Variability is ubiquitous within biological species, and gender is simply one manifestation of it.

Some cultural gender differences seem to have little to do with biology, such as the constantly shifting clothing and hair styles, the division of household tasks, and the recent gender shifts in some vocations – such as that more women are becoming medical doctors and attorneys, and more men are becoming nurses and early childhood teachers.

Biological Differences

Other differences are biological. It’s obvious that different reproductive roles require related differences in male/female bodies and brains. For example, although the hormones testosterone, estrogen, oxytocin, and vasopressin are present in everyone, females typically have more estrogen and oxytocin, and males have more testosterone and vasopressin. Further, females have a monthly menstrual cycle, and males have both daily and yearly testosterone cycles (high morning and autumn, low evening and spring). The more complex question is whether other significant normative brain differences exist that aren’t as easily related to reproductive roles.

The average male brain is slightly larger than the average female brain, but overall size may be less significant than internal organizational differences. For example, the corpus callosum that connects the two hemispheres is slightly larger in females, but the pathways that connect the sensory and frontal lobes within a hemisphere tend to be more robust in males. Females tend to have a more dominant left hemisphere, and males a more dominant right hemisphere. The auditory and olfactory systems tend to be more robust in females, and the visual movement detection system tends to be more robust in males. The hypothalamic structure that seems to regulate sexual orientation is larger in males than in females.

Further, our survival depends on our ability to understand how objects and systems function (systematizing capability), and to infer other people’s thoughts and intentions (empathizing capability). Although almost all males and females can do both adequately, males seem to have a slight normative edge in systematizing and females in empathizing.

Memory involves recalling the general concept and also the factual information that underlies the concept. Females seem to have an edge on factual recall and males on conceptual recall. Navigation strategies use geometric cues and the recall of landmarks. Males seem to depend more on geometric cues and females on landmarks. The typical male stress response is a fight/flight aggressive response, but in females it’s often a tend/befriend nurturing response. The significance of such biological and cognitive differences is problematic and controversial.

Interpreting Gender Differences

These and other reported overlapping gender differences create interpretive dilemmas. What we do know is that: (1) Males and females are structurally and behaviorally much more similar than different, (2) Differences don’t imply that one cognitive property or strategy is necessarily better than another. (3) Measurable differences must be interpreted in light of the within/between factor in normative research studies that compare group scores on human properties, capabilities, and behaviors (such as those listed above). The range of scores within each group is larger than the difference between the mean scores of the two groups. For example, consider height differences in large normally distributed male and female groups. The difference between the tallest and shortest person in each gender group will be greater than the difference between the average heights of the two groups of males and females. Thus, some females will be taller than some males in normative groups, even though the total population of males averages 7% taller than females.

Group differences thus only show group tendencies; they don’t predict for any single person in either group. So although it’s possible and appropriate to report general observations about normative male/female differences, it’s inappropriate to stereotype individuals — to use a general observation about a group to predict the properties, capabilities, and behavior of any individual male or female within the group. Further, it’s biologically inappropriate to argue that only genetic or only cultural factors (and not a mix of the two) led to the difference.

Key survival and reproductive tasks are regulated by a variety of interconnected conscious/subconscious brain systems. To state it succinctly, we must be able to successfully recognize and respond to novel and familiar dangers and opportunities that confront us within our space/time environment. We individually confront such dichotomous challenges, but different normative group capabilities can emerge over many generations – such as in populations who inhabit arctic and equatorial environments, and in gender groups whose cultural roles differ significantly.

Cultural Confusion

Gender-related cultural phenomena such as marriage, sports teams, and clothing styles are currently in flux. We went through a contentious period a generation ago in which many were disturbed when men started to wear longer hair; and we’re now going through a period in which some female students want to join the wrestling team or become the football team’s place-kicker. Same-sex marriage is perhaps just another step on a path of gender redefinition we’ve already been traveling for some time. Is marriage thus a phenomenon that should only involve two separate and pure gender categories, or should marriage be redefined as a personal public bonding commitment between two consenting adults, irrespective of the gender category each occupies?

So the issue comes down to how we should now define the concepts of male and female, considering that recent biological thought and discovery on the issue suggests that a fuzzy line both separates and unites the concepts of male and female, and especially as they relate to bonding behaviors.

Human Bonding Behavior

Human reproduction requires separate male/female sexual systems, but also a mutual willingness to engage in sexual behavior, and to bond if pregnancy results. Since child rearing involves an extended parental commitment, the impetus to engage in sexual behavior must be innate and strong. Call it love — an intense joyful attraction between two people that’s typically associated with romantic and familial bonding.

We’ve long associated love with our heart, but it really encompasses our entire body and brain, our entire psychological being, our entire lifespan – and researchers are now unlocking many of its intriguing mysteries. Romantic love appears to follow a three-stage lust-attraction-attachment sequence that emerged out of our strong biological drive to reproduce, and our need to nurture children over their extended developmental period. Couples in love who have no plans to conceive children (such as older or same-sex couples) apparently also follow the same biological/psychological sequence.

Scientists can now use brain-imaging technology to identify the specific brain and chemical systems that drive the complete process. The hypothalamus, caudate nucleus, nucleus accumbens, septum, and several frontal lobe areas are especially active when love is on our mind – and dopamine, norepinephrine, serotonin, endorphin, oxytocin, vasopressin, testosterone, estrogen, and pheromones are the molecules that seemingly jump for joy as they excite and inhibit the body/brain systems that regulate the behavior of love. So it’s party time all over our body and brain when love is in the air.

LUST is a somewhat abstract process that initially emerges during adolescence. Testosterone and estrogen provide an encouraging push to just go looking. Pheromones and personality predispositions probably assist in narrowing the field (such as to eliminate close relatives). Further, innate variations in the systems and molecules that regulate sexual behavior may bias a person’s focus to a same sex rather than to an opposite sex partner. Sometimes skyrockets go off immediately, and sometimes things heat up slowly – but at some point generalized biological lust leads to focused psychological attraction.

ATTRACTION is highly focused attention. One’s beloved becomes foreground and absolutely everything else becomes background. This is a time for fine-tuning initial impressions, and so the couple spends many hours checking out each other. If the attraction remains mutually supportive long enough to resolve any nagging concerns, the third stage of attachment kicks in.

ATTACHMENT is for the long haul, since it must maintain the relationship though inevitable distractions. Oxytocin, vasopressin, and endorphins become part of the bonding glue that maintains the relationship whenever temporary troubles arise. Wedding promises before family and friends, joint ownership of possessions, and children in need of parental love and nurture often provide a needed cultural bandage while a marriage hurt heals.

Children typically enter into a loving relationship with both parents at the attraction stage – the soulful gazing into a parental face, the oxytocin boost from nursing, the cuddling behavior that elevates oxytocin, vasopressin, and endorphin levels in both parents and child. Survival depends on children falling in love with their parents and their parents falling in love with them. The possibility of same sex bonding thus emerges in infancy — father/son, mother/daughter (plus favorite same sex relatives).

Innate forces create a situation in which they typically can hardly resist each other — until puberty, when lust kicks in and adolescents have to go looking elsewhere to help continue their species’ biological destiny.

Emerging Cultural Conflicts

Love is obviously more complex than this, and it encompasses many issues of appropriateness and legality that currently confront our culture. Some folks think that reducing love to neurochemicals and activated brain systems demeans the concept of love, but I think not. How wonderful to realize that falling and staying in love involves a perhaps forever-mystical synchronization of two complete biological organisms – and that’s what the poets and song writers have basically told us all along.

The biochemical complexities of love allow people who are infertile or homosexual to still fall in love and yearn to rear children, and people who have lost a partner through death or divorce to fall in love again. People are willing to adopt, teach, nurse, and coach the children of others. Two people who have few friends and seemingly no prospects will suddenly discover each other. Love is such a marvelously supportive and adaptable human property!

Since it’s in our society’s interest to encourage the stability of commitment, married couples now automatically gain over 1000 civil rights and benefits. Committed same sex couples have recently asked why they are currently denied the civil rights and benefits that accrue to married couples, given that their level of commitment to each other and their parental responsibilities might be equal to or even beyond that of many married couples.

Those opposed to extending marriage to same-sex couples typically do it on historical and religious grounds – arguing that marriage has historically been viewed as a male/female religious concept, and ought to remain so; and that strong religious sanctions exist against same-sex unions.

Same-sex marriage folks counter with the argument that couples must go to the courthouse for a civil license before going to a church building for the marriage ceremony, and couples can legally marry in a ceremony totally devoid of religious ritual. They further contend that a secular democracy should not grant civil rights and benefits to one class of citizens that it denies to another on the basis of religious beliefs.

Some argue that the issue should focus on the emerging awareness of the innate biology of sexuality, and others argue that biology is irrelevant – people ought to have a right to bond with whomever they choose. And truth to be known, we all know couples of whom we think, ‘What can they possibly see in each other’ — but they obviously saw something beautiful.

And that’s where this issue currently stands — contentiously complex and messy, with its resolution probably far down the road. The resolution of related church, school, military, and other institutional gender issues is similarly complex and probably distant. For example, Christian denominations with conflicting policies on the ordination of female clergy all claim to base their decisions on Biblical principles. No biological justification for such exclusion exists (but it is intriguing to note that female is the fetal default gender).

In the meantime, the next generation is growing up and looking for adult direction. Church workers and educators who work with adolescents can expect criticism no matter what they do or don’t do in assisting the adolescent search for gender identity and personal autonomy. Let’s work to insure that the emerging societal discussion will proceed in a civil and rational manner appropriate to a democratic society — devoid of name-calling and hatred, with empathy for all who are affected by the issue.

In this continuing discussion on gender, the church needs to realize that its historic antipathy towards homosexuality will become increasingly problematic, since homosexuals are becoming more militant in pointing out relevant biological discoveries and what they consider theological inconsistencies. For example, Christians believe that humans were created in God’s image and that God expressed pleasure at His creation. Why then would God specifically create a minority group who are biological predisposed to a supposedly grievous sin that’s grounded in love? Further, why would an omnipotent but loving God select some and not others into this depraved minority? If homosexuality is unnatural, why do non-human mammals exhibit a similar incidence of it? Why does a church that’s so adamant about homosexuality seemingly ignore other biologically oriented Biblical directives and prohibitions? The list of such challenges goes on.

Theologians have provided responses, but many people don’t understand or agree with the theological subtleties, and so interpret such responses as biologically ignorant and self-serving theological prejudice.

I suspect that most religious leaders wish these issues would just go away. They won’t.


Baron-Cohen, S. (2003) The essential difference: The truth about the male and female brain. New York: Basic Books.

Blum, D. (1997) Sex on the brain: The biological differences between men and women. New York: Viking.

Fisher, H. (2004) Why we love: The nature and chemistry of romantic love. NY: Henry Holt.

Fishman, J. (2000) “Why we fall in love” U. S. news & world report. Feb. 7. Pages 42-48.

Johnson, S. (2003) “The brain and emotions: Is love just a lot of chemicals?” Discover magazine. May, pages 70-76.

Lemonick, M. (2004) “The chemistry of desire” Time magazine. January 19, pages 62-118.

Ripley, A. (2005) “Who says a woman can’t be Einstein?” Time magazine. March 7, pages 51-60.

Rogers, L. (2001) Sexing The Brain. New York: Columbia University Press.

Sax, L. (2005) Why gender matters: What parents and teachers need to know about the emerging science of sex differences. New York: Doubleday.

Siegel, D. (1999) The developing mind: Toward a neurobiology of interpersonal experience. New York: Guilford Press.

Taylor, S. (2002) The tending instinct: How nurturing is essential to who we are and how we live. New York: Times Books.


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One thought on “Neurobiology of Gender

  1. I’m Postgrad Psych student and looking to specialise in Neuropsychology. When I eventually reach the end of my long and expensive university journey, my thesis will relate to a neurobiological explanation for transgender identity. There is a lot of demystification that needs to occur before transgender people can treated as ‘normal’ in our world.

    I enjoyed reading this article immensely! Thank you very much 🙂

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