Delusions of Gender (23 page)

Sommer also looked at older ways of looking for sex differences in language lateralisation. The left hemisphere processes auditory input from the right ear, and vice versa. If men, more than women, tend to use just the left hemisphere for language, then they should find it relatively easier to process words fed into the left hemisphere via the right ear (a phenomenon known as the right-ear-advantage). But Sommer and colleagues’ meta-analysis of these data, from nearly 4,000 participants, found no sex difference in the right-ear-advantage.
¹³
(Nor does the whopping dose of foetal testosterone experienced by girls with CAH seem to bring about a larger right-ear advantage.)
¹⁴
Another approach is to see how stroke damage to the left or right hemisphere affects the language abilities of male and female patients. While early studies found that men were more likely to suffer language problems (aphasia) after left-hemisphere damage, later and larger studies have not found this, including the Copenhagen aphasia study of more than 1,000 patients.
¹⁵
And as Sommer has pointed out, if
females also use their right hemisphere for language, they should have more language problems after right-hemisphere damage than do men. But they don’t.
¹⁶

So are males really more lateralised for language? It’s not clear why one would think so. And if men
are
more lateralised, it doesn’t seem to do them much harm. Several researchers have recently argued that gender differences in language skills are actually more or less nonexistent.
¹⁷

The supposedly larger female corpus callosum, a claim built on shaky foundations, is under no less serious dispute.
¹⁸
This research has been thoroughly examined and critiqued by Brown University professor of biology Anne Fausto-Sterling who, in
Sexing the Body
, explains the challenges of establishing the size of a particular structure in the brain. And a meta-analysis conducted by Katherine Bishop and Douglas Wahlsten in 1997 concluded that ‘the widespread belief that women have a larger splenium than men and consequently think differently is untenable.’
¹⁹
Summarising this literature in a 2008 review, cognitive neuroscientist Mikkel Wallentin concluded that ‘the alleged sex-related corpus callosum size difference is a myth.’ The culprit? Look no further than ‘the possibility of “discovering” spurious differences when using small sample sizes’, says Wallentin.
²⁰

So let us, with healthy scepticism, summarise all of this as clearly as we can. Nonexistent sex differences in language lateralisation, mediated by nonexistent sex differences in corpus callosum structure, are widely believed to explain nonexistent sex differences in language skills.

Confused?

We’ve only just begun.

The picture becomes only more puzzling when we look for evidence that men are more lateralised for visuospatial tasks. Some neuroimaging studies have found more lateralised activation in men of the parietal areas thought to be especially involved in this kind of processing. But others find no sex differences, and yet others find more lateralisation of activity in women.
²¹

Yet variations on a theme that contrasts a female, ‘floodlight’ brain that is global and interhemispheric in processing style with a male, ‘spotlight’ brain that is localised and intrahemispheric are everywhere. For example, a consensus statement titled ‘The Science of Sex Differences in Science and Mathematics’ links female ‘interhemispheric connectivity’ to an advantage in language skills and male within-hemisphere connectivity to superiority in ‘tasks requiring focal activation of the visual association cortex’, that is, visuospatial tasks.
²²

Simon Baron-Cohen has also taken up the spotlight/floodlight dichotomy. He and his colleagues tentatively suggested in an article in
Science
that the male brain skew towards ‘increased local connectivity’ makes it better suited to understanding and building systems. By contrast, the female brain skew towards ‘long-range’ and ‘interhemispheric connectivity’ is better structured for empathising.
²³
And Ruben Gur, a professor of psychiatry at the University of Pennsylvania who coined the floodlight/spotlight metaphor, explained to a journalist for the
LA Times
that brain science tells us that ‘[i]n a stressful, confusing multi-tasking situation, women are more likely to be able to go back and forth between seeing the more logical, analytic, holistic aspects of a situation and seeing the details,’ while ‘men will be more likely to deal with [the situation] as, “I see/I do, I see/I do, I see/I do.”’
²⁴
The implications of this difference for mental juggling may explain why Gur’s wife and collaborator, Dr. Raquel Gur, must take on the main burden of quickly putting together a meal for a hungry family. Gur
can
throw together a salad ‘[b]ut’, he says, ‘I can’t at the same time worry about whether this is in the microwave and that is in the skillet. When I do, something will burn.’
²⁵
Presumably, in that sad pile of cinders also lie the smoldering ashes of Mrs. Gur’s hopes of someone else ever being in charge of the meals.

Little surprise, then, with such scientific endorsements, to find popular writers picking up these ideas and running with them. Michael Gurian, whose Gurian Institute offers training to teachers, parents and corporations, becomes impressively quantitative
on the topic, explaining to educators that ‘[b]ecause boys’ brains have more cortical areas dedicated to spatial-mechanical functioning, males use, on average, half the brain space that females use for verbal-emotive functioning.’
²⁶
Meanwhile, Allan and Barbara Pease take the lateralisation hypothesis to its natural extreme in their book
Why Men Don’t Listen and Women Can’t Read Maps
, by claiming that the female brain is
so
unlocalised for spatial processing that it doesn’t even
have
‘a specific location for spatial ability’
²⁷
– thus neatly furnishing an answer to the second part of the title of their book. And why stick to language and visuospatial skills when, as certain academics have shown us, any gender stereotype can be pinned to sex differences in hemisphere use, in impressively scientific-sounding fashion? For instance, what began as women’s supposedly more bilateral language skills quickly transformed into the basis of womanly intuition and multitasking skills while, as John Gray explains in
Why Mars and Venus Collide
, men’s more localised brain activity even explains their propensity to forget to buy milk.
²⁸

But in all the excitement of having found a neurological explanation for male inconsiderateness and female underrepresentation in the Faculty of Mental Rotation, people failed to notice that the empirical ground had shifted beneath their feet. And they also forgot to ask a very important question: Why should a localised
brain
create a spotlight
mind
good at certain masculine tasks? And why should a global, interconnected
brain
create a floodlight
mind
better at feminine activities?
²⁹
And this brings us to the second problem with interpreting sex differences in the brain: what do they actually mean for differences in the mind?

Seeing that the average brain-weight of women is about five ounces less than that of men, on merely anatomical grounds we should be prepared to expect a marked inferiority of intellectual power in the former. Moreover, as the general physique of women is less robust than that of men – and therefore less able to sustain the fatigue of serious or prolonged brain action – we should also on physiological grounds be prepared to entertain a similar anticipation. In actual fact we find that the inferiority displays itself most conspicuously in a comparative absence of originality, and this more especially in the higher levels of intellectual work.

—George J. Romanes, evolutionary biologist and physiologist (1887)
¹

I
t’s always pleasant when data confirm predictions. But did George Romanes never once consider whether an African Grey parrot (with a brain weight of less than half an ounce) might outsmart a cow with a brain more than thirty times heavier? Did he really know not a single weedy intellectual, nor one muscular chump, to provoke him to wonder whether physical strength really was correlated with tenacity of ‘brain action’? Perhaps it was only natural that the brain scientists who meticulously measured men’s and women’s head dimensions, skull volume and brain weight should try to relate their findings to psychological differences between the sexes. But with the benefit of hindsight we can see that it was not just neuroscientific understanding they lacked,
but humility. ‘Optimistic’ is the only kind word to use to describe their confident assertions that differences in the engine power of male and female
minds
were being probed by tape measures, sacks of millet grain and sets of scales.

Today, we are no less interested in pinning our more sophisticatedly obtained sex differences in the brain onto the mind. ‘[H]ope springs eternal’, Fausto-Sterling wryly notes. ‘Is it now possible that finally, with
really
new,
really
modern approaches, we can demonstrate the biological basis of sexual or racial inequality?’
²
And, as neuroendocrinologist Geert De Vries has pointed out, it is intuitive to assume that males and females have different brains so that they can behave differently. With the discovery of differences in hormone receptors, or neuronal density, or corpus callosum size, or different proportions of grey and white matter, or brain region size, the instinct is to look for a psychological difference to pin it on. But the counterintuitive possibility that always needs to be considered is that sex differences in the brain may also ‘just as well do the exact opposite, that is, they may prevent sex differences in overt functions and behavior by compensating for sex differences in physiology.’
³
For example, a smaller number of neurons in a particular brain region can be compensated for by greater neurotransmitter production per neuron.
⁴

One very striking example of the principle that brain difference can yield behavioural similarity, discussed by De Vries, comes from the prairie vole. In this species, males and females contribute equally to parenting (excepting, of course, nursing). In female prairie voles, parenting behaviour is primed by the hormonal changes of pregnancy. But this leaves a mystery. How do father voles, which experience none of these hormonal changes, come to show paternal behaviour? The answer turns out to lie in a part of a region of the brain called the lateral septum, which is involved in the triggering of paternal behaviour. This part of the brain is very different in males and females, being much more richly endowed with receptors for the hormone vasopressin in the male, yet this striking sex difference in the brain enables male and female prairie
voles to behave the same. We can’t assume that even quite substantial sex differences in the brain imply sex differences in the mind. As Celia Moore has pointed out, ‘Some neural differences are inconsequential, because they are offset by other compensatory differences. Other neural differences are alternative pathways to the same behavioral end.’
⁵

In humans, one indisputable physiological difference between males and females is size – including the brain. Although there is overlap, men on average have larger brains than do women, and a large brain is not simply a smaller brain scaled up. Larger brains create different sorts of engineering problems and so – to minimise energy demands, wiring costs and communication times – there are physical reasons for different arrangements in differently sized brains.
⁶
From this perspective, ‘men and women confront similar cognitive challenges using differently sized neural machinery.’
⁷
The brain can get to the same outcome in more than one way. And in line with this, recent studies of brain structure have argued that it is not that
women
have larger corpora callosa, or a more generous serving of grey matter, relative to brain volume. Rather, it is people with
small brains
, male or female, who show this quality. As one group put it: ‘brain size matters more than sex.’
⁸
If this principle proves to be correct – there’s currently no agreed way of controlling for absolute brain size – then, unless we’re happy to start comparing the spatial or empathising skills of big-headed men and women with those of their pin-headed counterparts, we may have to abandon the idea that we will find the answers to psychological gender differences in grey matter, white matter, corpus callosum size or any other alleged sex difference in brain structure that turns out to have more to do with size than sex.

This, one would think, would secretly be a relief. This is not just because those gender differences can wax and wane, depending on the time, place and context. But also the very idea of trying to relate these kinds of structural differences to psychological function is fantastically ambitious, given that, as neuroscientist Jay Giedd and colleagues have put it, ‘most brain functions arise from
distributed neural networks and that within any given region lies a daunting complexity of connections, neurotransmitter systems, and synaptic functions’.
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