Mounting challenge to brain sex differences
sciencebulletin.org
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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.
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.
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?
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.
ideology
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.)
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.
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.
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...
The whole challenge is, "Can you remember that water should be horizontal to the horizon?" Remember that, and you pass.
_They_ say (http://www.sciencedirect.com/science/article/pii/S1053811916...) 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.