Science for the Unscientific

[Doobigetta]

I’m just trying to straighten my arguments out in my brain, and I seem to have a contradiction in my understanding- presumably because I’ve oversimplified something or glossed over something else. Please could somebody clarify for me.
On the one hand, there is no such thing as a lady brain. Male brains are generally bigger, because males are generally bigger. Other than that, it would not be possible to tell the sex of the brain’s owner by, for example, dissecting it. There can be very significant differences between individuals’ brain structures due to brain plasticity, but these are not intrinsically related to or caused by sex.
On the other hand, every cell in the human body contains a marker for the owner’s sex- XX or XY (or other in a very tiny number of exceptional cases).
These two statements seem to contradict each other. Please can someone explain in words that are easy to digest and regurgitate why they don’t, so that I can put a stronger argument forward than “I don’t know but actual scientists said so”.
Thank you...

One side is about physiology, the other about intellect/personality.

Physiologically male brains are larger, less folded and have XY chromosomes in every cell. Female brains are smaller, more folded (to enable the same number of connections from a smaller mass) and have XX chromosomes in every cell.

Physiologically male and female brains are different as are the rest of our bodies.

In terms of intellect and personality there is no such clear cut difference. At best you could argue men on average tend this way slightly more or less than women, but you cannot use these tendencies to differentiate between male and female from a brain scan because the variation within each sex is greater than the variation between the sexes and brains are plastic in terms of how they develop to process information.

Also not an expert, but what I think all that means is that there’s no sure way of distinguishing between a male brain and a female brain without doing the chromosome test.

Presumably other organs, e.g. heart, lungs, liver are similar, in that there’ll be individual variations, but nothing that makes them obviously male or female without chromosome testing.

I think it also means that you can't make claims as to the cognitive capability of a brain based on sex.

You can't say that females are going to be better than males at maths or that men are more visually creative or that females are more likely to watch football or that men are more likely to be interested in beauty

Although in some cases I think you can start to tell apart brains that have been trained in certain ways if you have a knowledge of the cultural expectations the person is raised under. Thinking that the London cabbie has a distinct enhancement on a certain part of the brain and are typically male. So you could compare two brains, think this one is more likely to be Male because it's a London cabbie Brain ( even then only more likely , not certain

Fantastic explanation Arnold!

I think simply, if you described an arm - eg. There's a hand on the end, it has 4 fingers and a thumb, each finger has a nail etc. you couldn't tell if that arm was male or female. If you chromosomally tested it, or knew the size, then you could.

People might say, oh, but if it has rough finger tips, or hair on the knuckles, then it's more likely to be a man's hand, but within men there are plenty with soft, hairless hands, and within women there are plenty with calloused fingers and hairy knuckles that it proves nothing, plus hair can be removed, and callouses/roughness come from use.

As for that non-specific arm, so go brains - there might be some formations that are generally more developed in men than women, but there is so much crossover, and so much is determined by use of that brain, that it can't be used to determine the sex of the body containing that brain.

Ah, so at a cellular level it is possible to tell what sex a brain is, but this doesn’t correlate to anything else. You can’t extrapolate anything about capacity, ability, strengths and weaknesses, etc. That completely makes sense and fills my gap, thank you all.

In fact it’s so bloody obvious when it’s explained clearly and I feel I need to explain that I know a reasonable amount about the Wars of the Roses. And books and stuff.

the variation within each sex is greater than the variation between the sexes
This is crucial, and cannot be stat4ed often enough.
The variation within each 'race' is greater than the variation between the 'races' is also true.

It's possible to tell the difference between male and female brains in different ways, here is one study.

www.pnas.org/content/113/14/E1968

A man and a woman of equal height will most likely have brains the same size.

We have all our genes in all our cells (forget gametes for now) so, for example, we have the DNA for our hair colour present in our liver cells. You can't dissect a liver and see what hair colour the person would have, because in the liver only the appropriate liver genes are being transcribed. Sex genes might be in every cell, but they aren't expressed in every cell.

It's possible to tell the difference between male and female brains in different ways, here is one study.

To a certain extent - but once they'd removed size-based measurements, they were getting it wrong about 1/10th of the time. And these were adults, who have been through 19+ years of societal training to grow different bits of their brains, so it is a little self-fulfilling, and not (to my mind at least) 'highly accurate' as they say.

If you could take baby's brains and reliably tell sex from a scan before they've been trained to be boys and girls, then I would completely agree, but being able to tell the difference, 90% of the time, in adults given known brain plasticity just isn't that convincing to me - I don't think it would be more reliable than from descriptions of an adult's hands for example.

I think you are trying to simplify it too much. What does "lady-brain" mean? Just things you'd see when you dissect, or things that we can image? What about behaviour or cognitive differences we measure in other ways, or things that operate differently under different hormones?

You could also ask, if men and women's brains acquire different characteristics due to the effects of existing in a female or male body, is that a lady brain or man brain? What if we cut out thigs that are more culturally arbitrary and just look at things that seem to be really true of the male and female experience of being embodied? After all, our sexed body is who we are, its not really separate from our brain.

Also - plasticity means it's very difficult to tell what characteristics of the brain might be ones that women or men acquire and which might not be, which is different than saying the latter don't exist.

The other thing of course is that there is a lot we don' know about the brain and our ways of knowing are pretty limited and crude. I'd not want to centre this idea in terms of my views on equality, it could easily be found to be wrong in the future.

To a certain extent - but once they'd removed size-based measurements, they were getting it wrong about 1/10th of the time. And these were adults, who have been through 19+ years of societal training to grow different bits of their brains, so it is a little self-fulfilling, and not (to my mind at least) 'highly accurate' as they say.

This is pretty much what I was about to say. (A lot of my day job involves calculations of skill for various ways of predicting things...)

What they're saying is "We can give you a system for betting on the horses which will enable you to beat the bookies on average - so even if you lose on one race, you're quids in on the other 9."

Basically, their proposed test has both low sensitivity and low specificity - Ben Goldacre wrote an excellent "Bad Science" column on this a few years ago:
www.badscience.net/2006/12/crystal-balls-and-positive-predictive-values/

Now admittedly, their test is at least not working with a "condition" which has a low incidence in the population - 51% of us suffer from the "condition" of being female, after all. But you have to ask "what are they going to say to that one girl in every ten they test who comes out as having a male brain?"

"Oops, sorry, you're actually a man?"

Or

"Oh dear, you seem to be showing masculine neurological traits despite being female, here are some pills to fix your improper brain function?"

Or perhaps

"Oops, sorry, our test is a bit crap. It works at a population level in the sense that if we're being asked to place £5 bets on every brain scan, with odds in the absence of any extra knowledge of 51 to 49 on, we'll make quite a lot of money, but at an individual level, it's actually a bit crap, because we can't guarantee that the sex our test thinks you are is the sex you actually are."

(Put it another way, you could do exactly the same with height. Average height for a woman is about 5'4", for a man is about 5'11" - consistently bet your fiver on "male" every time someone comes in with a height of over 5' 7 1/2" , "female" the rest of the time, and you're quids in over a long run of people. Still doesn't mean there are "male" heights and "female" heights).

Follow up - I think all papers in this sort of area should have to give their findings presented as frequencies.

A bit like the little infographics you're given for the nuchal fold test , with a grid of little people and a tiny corner coloured in with "correct diagnoses" and "false positives" and "misses."

So - take 10,000 women. Dear researcher intent on discovering sex differences, thereby cementing your international reputation: how many women out of this 10,000 woman sample does your fancy test tell you are actually "men" (or have "male brains" whatever the fuck that means...) If you're getting to the 100, or 1000 level, I would respectfully (or not so respectfully) suggest you're talking out of your arse and should go and take an elementary statistics course.

Also (another bugbear of mine whenever I venture into the neurological literature on sex differences) do not confuse "statistical significance" with "real world importance."

Get a big enough sample and you can make a really marginal difference between two populations statistically significant. But if it's really marginal, and you need a huge sample to even notice it, it probably doesn't have any real world importance. Certainly not the sort of importance you'd base, say, education policy or hiring decisions in the workplace on.

Size of brain does not correlate to intelligence, a cat's brain is 1/4 of the size of a diplodocus's brain. It's brain size relative to body size that matters but there are still variations, e.g. Einstein's brain was smaller than the average person (male or female).

Brain plasticity means that e.g. someone who spends their life thinking about and designing 3D structures (buildings, molecules, dresses, flower arrangements) will strengthen their spatial awareness. But that is not related to sex, and there's a complex mix of factors including stereotype threat (you tell people that a spatial awareness test is testing the skills involved in flower arranging then women do better in it than men, this is reversed if you say it is testing the skills involved in map reading). If you ask people to tell you their sex before they do a test they get different scores to if you ask them afterwards. The brain is plastic indeed.

Also (another bugbear of mine whenever I venture into the neurological literature on sex differences) do not confuse "statistical significance" with "real world importance."

First question our statistician at work asks us when discussing stats is 'this may be statistically significant but is it meaningful?'

This is quite a good (if intense) scientific article, which outlines the difference between male and female physiology. The male ribcage is deeper and has greater capacity than the female equivalent. The male heart and lungs are larger.

www.ncbi.nlm.nih.gov/pmc/articles/PMC5980468/

It's possible to tell the difference between male and female brains in different ways, here is one study.

I'd like to know why anyone wants to try to prove that there is a difference.