"It's time to celebrate the fact that there are many ways to be male and female.
Research published yesterday, showing that brains don’t come in male and female
forms, fits with what we know about gendered behavior."
"The research was inspired by a study with rats by Tracey Shors and colleagues,
published in the Journal of Neuroscience. She found that just fifteen minutes of stress
can change the “sex” of some features of the brain from the “male” to “female” form, or
from the “female” to “male” form. From this and dozens of similar studies – involving
different experiences and brain features – two important principles emerged.
First, a brain feature that is typical in females in one condition (a stress experience, say)
may be what is typical in males under other conditions, and vice versa. And second,
these interactions between sex and environment may be different for different brain
features, cells, and regions. For example, lab rats that have enjoyed a peaceful, stress-free
life show a sex difference in the density of the ‘top end’ dendritic spines (these transmit
electrical signals to the neuron cell body) in one region of the hippocampus.
(The female dendritic spines are denser.) But look at the same brain region in a group of
rats who have been stressed for just fifteen minutes, and now the dendritic spines of the
male rats are bushy, like those of unstressed female rats. Conversely, the “top end”
dendritic spines of stressed female rats become less dense, like those of unstressed male rats.
In other words, brief stress exposure reverses the “sex difference” for that particular brain
characteristic. However, this same brief stress has a different effect on the “bottom end”
dendrites of these same neurons. Here, male and female dendritic spines are identical,
so long as those rats have lived a stress-free life. But what happens if the rats are stressed?
There’s no effect on “bottom end” dendritic spines in females, but their density increases
in males, resulting in a sex difference.
Imagine, then, these sex-by-environment interactions affecting many different features of
every brain, from utero onwards. With each experience, some brain features change
their form, others do not, giving rise to unique combinations of forms. Not a “male brain”,
or a “female brain”, but a shifting “mosaic” of features, some more common in females
compared to males, some more common in males compared to females, and some
common in both.
This is exactly what the new study found for the first time, with colleagues from Tel Aviv University,
the Max Planck Institute, and the University of Zurich. They tested this prediction by analyzing
magnetic resonance images, which directly capture structural properties of the brain,
from more than 1,400 human brains from four large data-sets. They identified in each
data set the regions showing the largest differences between women and men.
Next, they defined a “male-end” (males more prevalent than females) zone and a “female-end”
(females more prevalent than males) zone for each of these regions, based on the range
of scores of the most extreme third of men and women, respectively. They found that
between 23% and 53% of individuals (depending on the sample) had brains with both
“male-end” and “female-end” features. In contrast, the percentage of people with only
“female-end” or only “male-end” brain features was small, ranging from zero to 8%.
Where this differs to past research is that it looks for the first time at whether or not sex
differences “add up” in a consistent way. While future studies should investigate whether
there is internal consistency in additional types of data, such as histological measures,
this study of structural sex differences found that these do not combine consistently to
create two categories of brains or a male-female continuum of brains."
"That brains don’t come in two forms fits with what we know about gendered behaviour.
With academics and commentators often arguing over the origins and size of sex differences,
an important observation by psychologist Janet Spence is often overlooked. This is that
correlations between “masculine” traits are weak or non-existent; so too for “feminine” traits .
Having one doesn’t imply you have another. For example, being gentle doesn’t imply
that one is also dependent. So do sex differences “add up” in a consistent way to create
two types of humans, or, like the brain, create “mosaics” of personality traits, attitudes,
interests, and behaviours, some more common in males, others more common in females?
The new PNAS study investigated this in over 5500 youth from three datasets.
Most differences between females and males are small, but this study looked only at
the largest differences (for example, worries about weight was the personal attribute
showing the largest difference, with about 80% chance of correctly guessing someone’s
sex on the basis of being above or below average concern; while for sex-stereotyped activities,
the largest difference was in the use of cosmetics, for which the chance of guessing sex
on the basis of their use was above 90% ). Even looking only at such behaviours, between
55% and 70% of people had a “mosaic” of gender characteristics, compared to less than
one per cent who had only “masculine” or only “feminine” characteristics.
This makes the notion of female and male natures as unintelligible as that of female and male brains.
Which of the many mosaics that males display should be considered the male nature?
Is it a profile of pure masculinity that appears to barely exist in reality?
Or is it time to let go of binary thinking and celebrate the fact that there are many
different ways to be male, to be female, to be human?
We can see social issues more clearly when we stop viewing them through the distorting
lens of sex categories, and start fully appreciating human variability and diversity."
I expect that many, if not most men, have long been culturally conditioned to regard themselves
as naturally superior to women, which means that these men are eager to believe that
they must be fundamentally very different--including in the brain--from women.
So I suspect that these (typically insecure) men feel threatened by scientific studies that
fail to bolster their sexist prejudices, and most of them will hasten to reject this study.