I think we’ve all heard this saying
“Men are from Mars, women are from Venus”.
The implication being that they are just completely totally fundamentally distinct.
But say you picked up a male brain and a female brain, and compared them.
Like you squeeze them in your pokemon, Prada man .
This is kind of a gross example.
I don’t think we should be playing with brains.
Put the brains down.
The question is if you looked at a male and female brain side by side,
would you be able to see any differences?
Well, the answer is super controversial.
And you probably wouldn’t be able to
tell with the naked eye, but like.
Maybe the better question is would it even matter if you could.
注意了 我们讨论的是性别的生物属性 而非社会属性
Now it’s important to note that we’re talking about biological sex here, not gender.
Almost all of the studies on brain anatomy have been done with people
whose gender identity aligns with the sex.
They were assigned with at birth,
which means we can’t really apply their results to people with other gender identities.
The same for people who are intersex,
meaning their chromosomes or reproductive anatomy
don’t fit the typical binary.
With that in mind though,
we can ask whether there are fundamental differences in
brain anatomy between biosex males and females.
And there are a lot of good reasons to ask that
how did it stereotypes
like the idea that males are better at math are one of them.
But there are differences between males and females that are pretty well supported.
For instance, females are more frequently diagnosed with disorders
like depression and anxiety and have higher rates of Alzheimer’s.
Biological differences in the brain, if they exist,
could help explain and treat these diseases,
and then there’s the fact that most of science just doesn’t use female animal models.
A 2010 study of sex bias in research found that
neuroscience was one of the guiltiest fields,
and that male animals were studied more than five times as often as female animals.
There are reasons for this, including the fact that
lab mice go into heat every four to six days.
我是说 你想想 雌性小白鼠每月来一次经前综合征
I mean if you thought PMS once a month,
was bad try factoring that kind of hormonal haywire into your nicely controlled scientific experiments.
That if human male and female brains are different
then not studying female animal models is a pretty big problem.
So, are sex related anatomical differences a thing or not?
好吧 既有 也没有
Well, yes and no.
The one consistent finding is that male brains are bigger on average than female ones
which make sense because generally
男性大脑更大 体型更大 身体各部分也较大
male heads are bigger. Bigger bodies, bigger body parts.
Other studies suggest that there are differences in specific brain regions.
Or that for females some regions have thicker cortices.
The folded grey matter on the outer edge of the brain
that we use to do our higher-level cognition.
But findings vary by study and all of them depend on
whether or not you correct for the larger size of the male brain overall.
When you do some of the results disappear,
and some stay the same and some even flip which sex is larger.
Though again, different studies have had different results.
And whether or not to do that kind of size correction,
it’s still hotly debated by scientists.
Some researchers point out that
larger brain structures are still larger brain structures
no matter what size your body is.
Those extra neurons got to be doing something right
and we make all this fuss about our brains
being bigger than those of other primates.
Because we assume that size matters.
But it’s not like we think sperm whales are vastly more intelligent than we are,
even though their brains are more than six times the size of ours.
So most studies investigating behaviors or disease conditions
look at the relative size instead.
Indeed the very fact that a lot of sex differences disappear,
once you correct for relative head size
suggests that maybe it’s worth taking a second look at.
For example, a 2018 study
which is perhaps the most comprehensive to date,
looked at the brains of 2,750 females and 2466 males.
And found that anatomical differences did exist
and were statistically significant.
On average, females had thicker cortices in 48 of the 68 brain regions examined.
But males had larger brains and larger brain regions and structures.
When the size of the brain was accounted for though,
the sex differences and the size of most of these regions disappeared.
So do the size differences in structures,
比如 海马体 尾状核和丘脑
like the hippocampus caudate nucleus and thalamus.
And females ended up having larger relative volumes for
10 regions as well as the right nucleus accumbens.
So the differences in size of these structures absolute or relative were small
and there was a lot of overlap.
So if a particular structure was really big, or really small,
it might be associated with a particular sex.
But plenty of different sizes for a given structure
could be considered totally normal for males or females.
And previous studies had found that
while there are average differences between the sexes,
individuals don’t necessarily have male or female brains.
Researchers in a 2015 study of 281 brains found that
individuals often have like a quote and unquote mosaic
of male-ish and female-ish brain characteristics,
rather than all their structures tending toward one sex.
What conclusion can be drawn from all of this?
Well, despite all the controversy,
there might be some small differences on average between male and female brains
and that does kind of make sense.
After all, males and females have different chromosomes
and are exposed to a different set of hormones
both prenatally and throughout our entire lives.
Despite that though, a lot of social psychologists and sociologists
point out that it’s impossible to know
how much of these sex differences come from biology
and how much come from environmental influences.
The brain is famous for being plastic after all,
and it makes sense that if playing video games alters your brain,
how you were raised and treated and act, alters your brain too.
But there’s also an assumption underlying all this debate
which is rarely questioned that
these differences correlate to sex specific differences in cognition or behavior.
The thing is there’s not much evidence that, that’s true.
And there might be a reason for that.
One interesting theory some psychologists have is that size does matter.
But that the anatomical differences between the sexes compensate
for any cognitive differences that might otherwise arise because of sizing.
So that relatively large right nucleus accumbens or the thicker cortices of females,
don’t make them act or think differently than males.
It ensures they don’t despite the male’s larger noggins.
And even if size does matter bigger isn’t necessarily better.
There simply isn’t a lot of evidence that actually connects
anatomical differences in brains to behavior or cognition.
Unless you’re talking about things,
like malformations, lesions or serious brain damage.
And remember phrenology.
That’s super cool trend in the 1800’s of using the lumps and bumps
on a person’s head to make judgments about their thoughts and personality.
Yeah, that one made everybody look silly.
So as usual, there’s a lot more work to be done to figure out what all this means.
But for now, you could be pretty skeptical of anyone trying to
use brain anatomy to justify any argument about differences between the sexes.
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