
Mounting challenge to brain sex differences - upen
http://sciencebulletin.org/archives/9423.html
======
xaa
I work in a area related to this: neural aging. Many of my collaborators are
constantly looking for gender differences in the basal brain and WRT the aging
process.

They are encouraged to do this by a semi-recent NIH policy strongly
encouraging experiments to include both genders because of a perception that
females were being left out of biological research. I don't think that is
true, because for example NCBI GEO samples are virtually equally balanced
between M/F, but hey, NIH has to play along with politics to some extent to
get funding.

So once investigators have gone to the trouble and expense of including both
genders in an experiment, they will naturally do the analysis comparing
genders. They will perform lots of comparisons, sort the p-values, and declare
some differences. And to provide a fig leaf for readers concerned that our
time is being wasted, they will say these differences which are probably often
statistical artifacts, are "important" for some nebulous, rarely explained
reason.

This is not to say there are NO differences. In the context of aging, female
humans live several years longer than males on average, and there are some
biological reasons for that. It's just that it beggars my imagination to think
that core biological processes unrelated to reproduction would have vast
differences between genders. Evolution, it should be remembered, predates
gender by a long time. More importantly, if we are trying to understand core
biology, we should be focusing on the main effect IMO rather than the
relatively minor gender differences.

~~~
omonra
"Evolution, it should be remembered, predates gender by a long time."

1\. Good point - gender is 50 years old (first used in 1963).

2\. What about other, non-human organisms? If we leave humans out of it, there
have to be significant differences in brains between sexes of different
species.

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speeder
That article has some kind of hasty judgement, saying that because a tiny
brain structure is equal in men and women it is evidence for the whole brain
being the same...

Yet what about other obvious evidence of the differences, like the fact that
men brains are usually obviously heavier? Or the differences in overall
distribution of grey and white matter? or that many neurological disorders,
like aspergers syndrome, have different symptoms depending on the sex?

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mordocai
I didn't read the actual study, but from the article they are basing this on
the amygdala size being bigger but the male brain also just overall being
bigger.

My question is: What rules out the bigger size itself (irregardless of overall
brain size) causing differences? Perhaps, the ratio of amygdala size to brain
size does not matter but rather just the absolute size.

~~~
carsongross
_> My question is: What rules out the bigger size itself (irregardless of
overall brain size) causing differences? _

ideology

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btilly
They are demonstrating that they didn't find difference. Not that none exist.
They do exist, and this is easy to verify with the Piaget Water Level Task.

The task is simple. Draw a cup like |_| and then the same tilted perhaps 30
degrees. Hand the pictures to someone and ask, "If they are both half-full of
water, draw the water line." Conduct this experiment on 5 random adult friends
of each gender.

With extremely high probability, you will now have very strong evidence that
there are very real brain sex differences. No demonstrated ones that seem
particularly important to me, but clearly they exist.

(I first encountered this as part of a pair of questions, this one and another
which women got and men didn't. I thought it was BS, a month later gave this
one to my then girlfriend, and have never again found the other. Incidentally
there is no difference on performance in this one until puberty. Interestingly
the odds of success for gay/trans people are between straights, suggesting
that their brains tend to be mixes of "normal" in more ways that one.)

~~~
majewsky
Can you share the expected results? I don't have 5 random adults with me right
now. ;) And Google does not turn up anything useful (only paywalled papers).

~~~
btilly
Around 90% of men find the task trivial. About 70% of women can't do it.

Additionally women who can't do it when presented with the same task years
later remember that there is a trick, but have trouble remembering it and
still can't do it.

I have never met a programmer, male or female, who found the task anything
other than trivial. I have no idea why, and no idea whether this fact may be
correlated with the gender imbalance in programming.

~~~
tzs
Did you specify about 30 degrees because the trivial method fails if the tilt
is too large?

I see a trivial solution, but it only works if the ratio of the water height
before tilting to the diameter of the cup is greater than the tangent of the
tilt angle.

~~~
tzs
OK, I've done some reading on this, including a several year old blog entry on
this topic by the person who brought it up here [1], and it looks like I
misunderstood what is required to consider the problem solved. I took it as
requiring that volume, shape, and orientation of the water all be correct in
the tilted cup, and assumed that people who fail are probably getting shape
and orientation right but are not getting the volume right.

Apparently, the failure mode is typically to get the shape and/or orientation
wrong, and you pass if you get them right. Volume doesn't have to be right.

[1] [http://bentilly.blogspot.com/2010/08/piaget-water-level-
test...](http://bentilly.blogspot.com/2010/08/piaget-water-level-test.html)

~~~
btilly
Exactly.

The whole challenge is, "Can you remember that water should be horizontal to
the horizon?" Remember that, and you pass.

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throwaway83834
I wonder what the transgender community has to say about this given their
efforts to prove that there are differences.

------
vorotato
TLDR; Evidence is piling up that the male brain / female brain concept is
nothing more than a myth.

~~~
pbhjpbhj
That's a terrible synopsis of the linked information.

_They_ say
([http://www.sciencedirect.com/science/article/pii/S1053811916...](http://www.sciencedirect.com/science/article/pii/S1053811916307431))
that as the male brain is 10% larger in the studies covered by their meta-
study the fact that the male amygdala, a small portion of the brain, is 10%
larger in those studies means it can be normalised out and we can say that the
male and female amygdala are not different.

This might be the worst reasoning I've ever read in a scientific paper.

Presumably the full study has fine structure detail comparisons that show that
the male amygdala is merely an enlarged version of the female one, that there
is no additional smaller structure in one than the other (which would be
strange, meaning male neurons/blood vessels/etc. were larger, which would
itself be a difference that warranted study).

FWIW the highlights make the reverse claim implicitly as it says male amygdala
are 10% larger but their brains are 11-12% larger. That would give the
conclusion the male amygdala is smaller as proportion of brain volume. So, the
quoted figures contradict the conclusion just within the abstract, that seems
like bad form.

The abstract says:

>These values correspond to less than 0.1% larger corrected right AV [amygdala
volume] and 2.5% larger corrected left AV in males compared to females.

2.5% isn't even possibly significant though right, like the "we share 99% of
our DNA with chimps" statistics [however misguided they are].

Now, sure the amygdala could have identical function in human males and
females, but this study doesn't seem to move any closer to that conclusion if
the highlights and abstract are representative.

