Are women’s brains fundamentally different from men’s?

  • Is a male brain different than a female brain?

    Yes, it’s true in a very generalised and subtle sense. For the most part we are functionally and morphologically the same. The broad outcomes, be they cognitive or physical are very, very similar and overlap significantly.

    But yes, subtle differences can be found. After all, everyone’s brain is different. And just by sight alone men and women look different. It’s a popular way we tell ’em apart, isn’t it?

    But looks aren’t everything.

    We all vary by size, shape, ability, motivation, interests, age, underlying biology, developmental timing, experiences and all the rest. It’s complicated. So we generally work off averages rather than dwell on specifics.

    In that way, broadly speaking, men tend to be larger, heavier and more muscular, women more gracile and slender; and that’s reflected even in the shape and size of their heads. Men’s heads are just a bit… thicker? No, that doesn’t sound right. Bulkier, then?

    Given that visible difference, it would be no surprise to find a morphological difference or 2 in the way our brains are packaged into those slightly, if noticeably, different brain cases. Men have a bit more head-space, on average, to work with for example. Hence the “bigger brain” is born. Sigh.

    There’s no denying some underlying biological basis for our sexual differentiation here, but determining how much, when, and how remains a work in progress.

    But does it matter? Male and female brains seem to work just as well.

    And it’s not just by packaging that we vary. Again it would be no surprise to find subtle neurological differences based on different sex roles, particularly with regard to the specific needs of child bearing.

    There would possibly be some specific female-only reflex arcs, timing, pattern-generation and pain mitigation “wiring” that men simply don’t need (at the moment, anyway). Perhaps that unnecessary detail was wiped clean during development, or is just all curled up and forlorn like a compacted Y chromosome.

    Speaking of which, of course the default setting is XX rather than XY, so “female” is likely the preferred fall-back, the fully-featured version if you like (minus an extended externality or 3). Anything decently useful on Y, other than the toggle switch for “male”, was translocated to X before the genetic rats jumped ship.

    That’s not to say Y isn’t full of fascinating genetic left-overs, it’s just that there’s only about 45 of them.

    Which is to say that Y has lost/misplaced 1,393 of its 1,438 original genes and picked up perhaps only 160-odd “new” stragglers along the way. Around 70 of the 200-odd genes “onboard” Y actually encode for proteins. The rest are observers and hangers-on I guess.

    Which seems to suggest X has all the good stuff and Y has only got what it needs to stay viable and distinct as a male “on” switch. It’s certainly true that no vital genes reside only on the Y chromosome, since roughly half of all human beings (yes, the female ones) do not have a Y chromosome at all.

    You can argue over that one as much as you like.

    But the details hidden within such otherwise compelling generalisations are poorly understood and any broad conclusions often not compellingly linked to, well, much at all, let alone any specific human behaviours.

    Indeed a lot of what passes as “fact” in the mass media is conjecture, often cribbed from the most recent half-relevant imaging study; or it is ‘popular wisdom’ copied from one article to another, each using the previous as ‘source’. Sort of a pop-science version of a Ponzi scheme.

    Of course there are some more comprehensive, published studies involving larger sample numbers from broader demographics, sometimes involving a degree of longitudinal study as well. From those we can see that there are indeed some physical and demonstrable brain differences, broadly speaking, and some correlation with observed behaviour as well.

    But not a lot. Nor even compellingly so.

    It remains very difficult to unpick the effects of our socialisation, our social and cultural programming, from any such observable – and small – physical differences.

    If genetics alone doesn’t really explain much, socialisation certainly does.

    From birth (or perhaps even before) we are socialised into our individual lives, shaped, guided and programmed to live according to what we see, feel and explore.

    We respond in individual ways to this powerful force applied to our very plastic, adaptable brain. It involves everything we see, hear, feel and do, from sources such as our parents, relatives, friends, neighbours and the media. It’s not just rules-based or “formally learned” stuff, it’s often far more subtle. It also includes our language acquisition.

    We observe, we hear and we learn. And it changes us.

    In this way we pick up our localised “culture” and “values” without necessarily even thinking about it. Just imagine our behaviours – including our conception of “male” and “female” – without that socialisation. It even defines what we mean by male and female, far more so than our external genitalia alone might suggest.

    What we do in life is literally recorded in our plastic (as in changeable) brain structures. If by our cultural norms we divide ourselves into male and female groups at an early age and program ourselves into separate sexual, social and working-life roles then this will be reflected variously by neuronal growth and density in differing sub-regions of the brain.

    Given that fact, it should be no surprise that studies of small groups of adults of a similar culture will display a predictable sexual dimorphism in their brain structures.

    Socialisation doesn’t explain everything – but it can explain a lot.

    Still, not everyone is on board with the power of socialisation.

    Another hypothesis lends more weight to prenatal sexual differentiation of the neural tissues. This includes the neural-endocrine axis associated with reproduction and sexual behavior and is somewhat analogous to the hormonal mechanisms involved in genital differentiation, but result instead in the pre-patterning of the sex-related neural net, if you like.

    Male and female “behaviour templates” are thus built into the affected neural tissue. In terms of time, these ‘sexualised’ neural tissues are the last to differentiate, the process starting very early, perhaps by 5 weeks after fertilisation, and continuing after birth with culmination post-puberty.

    To my mind that seems another long bow to draw but it has its adherents. You could link it in with research describing the association between neurohormones and neural tissue, as well as analogs based on other endocrine functions and behaviours.

    Perhaps the truth is lies somewhere between the biological and the environmental.

    Further reading:

    There is some truth buried underlying the speculative conjecture. Prior to birth we are exposed to powerful sexual hormones that change us from a ‘standard template’ if you like, into what we think of as our sexual – or gendered – selves.

    A detailed review with a reasonably controversial “sexualised neural tissue” hypothesis may be read at the Pacific Center for Sex and Society.

    Taking a few steps back, human sexual development is chromosomal at first, leading to gonadal, then phenotypic (the secondary characteristics we typically get so fond of). The developmental journey takes years, and feels even longer at the time. Along the way the brain gets involved, as it does, and we build up a repertoire of associated behaviours, appropriate and otherwise.

    We all start the same though, with both sets of standard ducting available for future embryonic development as either a male or a female. All it takes is a Y chromosome, generally, although even that is not necessarily true. What you really need, gonad-wise, is just one gene – the SRY gene – and that too may mutate or transfer to an X and confound things a bit. Roughly 10% of the time you do get a variation of some kind, even if we don’t notice it.

    In any case that’s 1 gene out of a Human genome of 23 chromosomes and maybe 20,000-25,000 human protein-coding genes out of a total of 3,250,000 base pairs. I’m not saying that as genes go it’s insignificant, in fact it’s very significant and a personal favourite; but there’s a lot more going on here than just sex and gender.

    Unless you are thinking that there’s one gene that rules them all. But there isn’t.

    What I’m trying to do is to sketch in some context and set up some sort of perspective, I guess.

    Anyway, to labour the point or to delve deeper (take your pick) the sex chromosomes and presence/absence of that single SRY gene kick a few significant things off. Around 6 or 7 weeks the chosen path is made manifest internally and the deckchairs get re-organised, as it were. New plumbing is ordered and hormones get secreting. All is good.

    Time passes and the external bits form. With the added presence of potent Dihydrotestosterone we get the male progression, its absence resulting in the female. The male’s testosterone production peaks about week 16, after which it declines to roughly match the female fetus. Presumably the developing brain is thoroughly soaked as well, but whilst it’s often described as “the biggest sex organ” it doesn’t seem to respond as dramatically as the more user-specific parts.

    The male is also producing Mullerian inhibiting substance: a gonadal hormone with multiple functions, basically doing some after-party cleaning, whilst the female is producing estrogen. Bear in mind the mother’s estrogen levels are way higher and are available to both the male and female.

    How does that affect the brain’s development? Well there’s a question.

    Both male and female brains, if you like, are soaked in the mother’s estrogen throughout. Now if we assume the testosterone makes a difference, then presumably the estrogen does too.

    Of course the developing human doesn’t run off and get a prescription filled at the local chemist (or pharmacist or drugstore or whatever you want to call it). There’s a range of production here that varies by individual, by mother, by environment, by diet.. a range that goes from go to whoa. So whilst there’s a gross average value for these things, it really doesn’t mean much on an individual basis. We all get a different dose of everything.

    More speculatively, a substantial product of testosterone metabolism in males is estradiol, and the actual conversion of testosterone to estradiol depends on the amount of available body fat. The more fat, the more estradiol. (In case you aren’t with me yet, estradiol is the primary female sex hormone.) Bear with me.

    It’s possible that a nutritionally-richer Western lifestyle may impact estradiol levels in developing boys, which historically have been typically much lower than in girls. If so, that’d be an interesting study, especially if you believe that male and female brains are “different”. (More than just brains would be visibly affected.)

    Perhaps over time and with the ‘right’ diet they may become less different?

    Intriguingly estradiol is produced not just by endocrine glands but by non-endocrine tissues like fat, breast, liver and neural tissues, including the Grey (cognitive and processing tissue) and White matter (active modulating and coordinating tissue) of the brain.

    I don’t know what that means, functionally, but it’s interesting nonetheless. Bear in mind that when you read about the grey/white matter variation between males and females (it’s a commonly promoted ‘difference’) the context of the source study is often lost (that the studied areas are highly focused and regionalised, for example, or the study is small and unrepresentative) and untested speculation overtakes confident conclusion.

    Grey matter decline (or absence) has been associated with age, with smoking and with excessiveing of pornography, just to name a few. No surprise it crops up in male vs female brain studies too.

    One study into grey matter investigated the association between poverty and

    neural development. An association was shown between relative poverty and

    lower volume and surface area of grey matter in children growing up in

    poverty. Another related study found no significant difference in total grey matter of newborn babies, but at the age of 2 a significant difference in grey matter was found, and by the age of 4 this difference was further pronounced, the decline correlated with poverty as well as age. Further work revealed that a study of children living in poverty had a regionalised grey matter
    3-4 % below what was deemed the

    developmental norm for the corresponding age.

    So it’s not just a male-female divide, if it’s that at all.

    Anyway, back to the journey. We all get a surge of sex hormones for a few weeks after birth. We don’t really know what that’s all about. Perhaps it’s just a test run or some fine-tuning before the long, stable wait until Puberty.

    And then things get really interesting. The brain and the hypothalamus in particular start producing the gonadotropin-releasing neuro-hormone, which results in a cascade of by-products that stimulate the pituitary gland, leading to large doses of testosterone and estradiol. You get growth and lots of changes.

    Worth implicating the adrenal gland, too. When stimulated in the ‘right’ way they produce androgens that may be processed and converted into sex hormones in the testes and ovaries. The balance of androgen production is going to vary individually and over time, of course, so that too will possibly be reflected in your “male or female brain” hypothesis. Just sayin’.

    Presumably puberty is where our brains get thoroughly addled again by all of these surging hormones. But a lot of tentative socialising (of the obvious kind) goes on as well, so picking out real physical differences and their behavioural effects from all of the cultural, social and attitudinal differences that happen at puberty would be a minefield to explore.

    Given all of the (quite obvious) physical changes during puberty, including real alterations to physical appearance and growth rates of males and females, it would be surprising if all of the underlying hormonal surges didn’t impact the brain in some way, if only incidentally.

    Typically, however, such changes must stand the test of time, represent a functional advantage or at least be neutral in impact, or be lost.

    Looking at these sexually dimorphic changes in gross, average morphological terms, the pubertal changes appear to have a functional, adaptive purpose beyond signifying our readiness to reproduce. By the end of puberty, adult men have will generally have heavier bones and nearly twice as much skeletal muscle, on average, as women. Arguably for labouring, hunting or protection purposes. And women have similarly important physical changes in support of childbirth.

    Presumably the evolutionary pressures that selected for these traits were at full force a long time ago, as they largely appear “as is” both on most of our closest living primate relatives as well as on many of our own far distant and fossilised relatives.

    Some of the pubertal bone growth, particularly so in the shoulder width and jawline is disproportionately greater in the male, resulting in noticeably different male and

    female skeletal shapes. Other morphological and adaptive changes include the greater lean body mass of an average male. Putting that muscle mass and bone structure to good use, I guess, with hard manual labour and athletic pursuit of fleet-footed prey. Whereas female adaptations tend to reinforce physical flexibility and immediate survival of both mother and child.

    But what would be the hypothesis for supposed sexually dimorphic brain adaptations?

    If they exist, and they appear to exist in some subtle ways, then they could be neutral changes that don’t affect our overall success. They may be deleterious only later, after successful reproduction, or be conserved along with genes that are beneficial or essential.

    Whilst it’s possible to imagine the selection of supposed maternal qualities of patience, care, virtue and early education for females, it’s just as likely that males could use (and display) such qualities at times, too. And we have arguments here over what exactly are the mammalian maternal qualities, beyond the obvious basics of childbirth and initial support. You could argue that either sex could suck on the oxytocin and bond sufficiently anyway. Stereotypes begone!

    And supposed male adaptations for spatial awareness during ‘hunting’ are equally balanced by similarly supposed female space-mapping requirements when gathering food. You could make a case for a distinction, of course, but it’d be a long bow, as it were and more stereotyping.

    If you want to study ‘male vs female’ brain development, you could look at 5-alpha-reductase deficiency, where children are born ostensibly male but feminised, are often socialised as such but quite naturally (and frequently, if rarely in general population terms, in some places) develop into males during puberty. There could be some answers there, or at least plenty more interesting questions.

    And as I keep saying, we are all different. Indeed males and females overlap in abilities, be they mental or physical. All of the above just attests to the complexity of it all.

    The differences found so far are relatively small in comparison with what is actually “the same”. What the sexes have in common is overwhelmingly similar, but few seem to think that’s significant for some reason. We jump on the differences because that seems to fit our stereotypes better.

    Bear in mind, we are all different. There is no one “human brain”, just a gross generalisation of the morphology based on averages. The functional regions as we know them are historically based on experimentation, surgery, lesions, animal studies and, in comparison with the number of people who have walked this Earth, a relatively small overall sample.

    To the best of my admittedly limited knowledge, neurosurgeons still “test the wiring” before trusting the grossly generalised ‘road map’. As I said, we are all individually different, and sometimes we are very different. It’s worth checking before slicing.

    So when we compare male and female brains we are not comparing them to a rock-solid baseline, rather we are comparing one smaller set of gross morphological averages that vary with age and demographics with another larger set of gross morphological averages that vary with you-guessed-it.

    As I say, just bear that in mind. The actual range of brain-related physical morphological variations between males and females will likely overlap, just like males and females generally overlap in functional, behavioural and physical terms, especially so before puberty, when boys and girls are often more similar in terms of risk-taking and activity levels. You can even see that played out in injury rates by sex and age. There’s a point where – broadly and statistically – either girls simply and ‘naturally’ lose interest in outdoor risk-taking or are encouraged to ‘stop acting like a tom-boy’ (for example). The injury rate declines sharply, anyway.

    Of course humans are generally arranged into physically different male and female body forms, and with the onset of puberty they develop further differences, resulting in primary and secondary sexual characteristics and a general sexual dimorphism. And whilst it’s on average a reliable and predictable process it’s also individual by degree and timing. Again, big overlaps.

    It would be surprising if this powerful process of development didn’t affect the brain in some way. And again it would be surprising if it wasn’t very individual, with the same big overlaps between the groups.

    Which leads me to ask, are we looking for gross brain-based morphological differences before, during or after puberty? Or before birth for that matter. Do the studies referenced (by the mass media especially) address these developmental stages, their timing and individuality? Do they relate any observed morphological differences to actual behavioural differences? Do they take into account socio-economic demographic factors in the sample? What about cultural difference and socialisation, in the sense of how as a society we “program” ourselves into male and female “expectations” and compartments?

    Yes? No?

    Many of the studies I have read don’t attempt any of this, although most suggest that further studies along these lines ‘need to be done’. As excellent and thought-provoking as they are, compellingly complete they generally are not.

    So, back to the question. Another concern is the actual measurable differences in function. Are male and female brains (as it were) generally, functionally different? Not so much. When given equal opportunity, our brains, be they hosted in male or female bodies, seem to be able to do much the same thing at similarly high levels of function.

    The brain is a plastic, adaptable and changeable thing. We have known this for a long time now. What we do and think leaves a physical trace on our brains. Over time our actions, framed as they are within our cultural restrictions and personal choices accumulate and shape us.

    So taking snapshots of what our brains “look” like at any one time and from those images making rock-solid statements about “differences” is premature and naive. But of course researchers typically don’t tell us what they think it means, only what it could mean. The mass media then cut and paste as needed.

    Indeed many of the major and popular “differences” are based on just one or 2 studies, often involving just 20-odd participants, all from a similar socio-economic demographic. Too often just the abstract or a press release is quoted, not the detail. And a lot of important context is lost in the process.

    And once that purported “fact” makes it into “the wild”, even if it’s not even what the researchers actually said, it gets repeated as it is, endlessly.

    Basically the real-world outcomes are pretty much the same – smart, capable males and females abound – and what we find is just a few quibbles over what some sub-regional variations mean, and how, why and when they form. It’s possible that one or more of these variations is really significant, but we don’t actually know that for sure.

    Most of the published work done so far to image the living or to section the brains of deceased people leaves more questions than answers. Almost universally the researchers make conclusions that “may” indicate or “suggest” a link between observed physical differences and correlated behaviours. Rarely do they include compelling follow-up studies that test such links. They usually agree that further study is required.

    Yet that doesn’t stop the mass media making hay about the latest press release that “proves” that male and female brains are distinct, or that any such observed physical differences matter.

    In the scientific literature there are studies that show evidence for far bigger differences in brains between age groups than between sexes. But many studies don’t look or sample longitudinally. They are focused instead on similar ages, similar demographics and a small sample size.

    For those interested in genetic puzzle of human sexuality, check out the SOX gene family and the male-specific transcription factors (mainly SOX9 ). interesting also is that Forkhead box L2 is required to continue down the female path of development. So the system is not as simple as as yes/no presence of the SRY gene. The FOX proteins in general are relevant here too.

    DAX1 – a testis antagonist and general sexual regulator, if you like.

    Arcuate nucleus – the ticking clock of the hypothalamus?

    Human sexuality


    Androgen receptor

    Estrogen receptor

    Transcription factor – vital mediating ingredient in the DNA mix.

    Sex differences in the structural connectome of the human brain

    Brain Differences Between Genders

    Men and women’s brains are ‘wired differently’ – BBC News

    How Men’s Brains Are Wired Differently than Women’s

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