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Male and female brains are wired differently according to this article:

Maps of neural circuitry showed that on average women's brains were highly connected across the left and right hemispheres, in contrast to men's brains, where the connections were typically stronger between the front and back regions.

But since learning in the brain is associated with changes of connection strengths between neurons, this could be or not the result of learning. What about physical differences from birth? Are there differences in size, regions, chemical composition, etc. from birth?

Pablo
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    Answering this question meaningfully requires distinguishing whether you're asking if the statistical properties of brain characteristics differ by gender of the population you're looking at, or whether there are fixed relationships between gender and specific brain characteristics. Considering how complex gender itself is, the latter seems like an extraordinary claim and highly unlikely – R.. GitHub STOP HELPING ICE Nov 28 '17 at 01:52
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    This is just for a laugh : https://m.youtube.com/watch?v=0BxckAMaTDc – Solar Mike Nov 28 '17 at 14:08
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    As an FYI, when discussing issue like this, it's useful to remember that in a lot of instances, intra-subpopulation variance can and often is far larger than inter-subpopulation. In other words, even if/when the brains (or other characteristics) may differ "on average" by X; but within both males and females, they differ from one another by far more than that average X difference. – DVK Nov 28 '17 at 15:48
  • @DVK: That's closely related to what I was trying to get at. – R.. GitHub STOP HELPING ICE Nov 28 '17 at 22:02

3 Answers3

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Short answer
Yes, men and women's brains are different before birth.

Background
First off, learning effects versus genetic differences is the familiar nature versus nurture issue. Several genes on the Y-chromosome, unique to males, are expressed in the pre-natal brain. In fact, about a third of the genes on the Y-chromosome are expressed in the male prenatal brain (Reinius & Jazin, 2009). Hence, there are substantial genetic differences between male and female brains.

Importantly, the male testes start producing testosterone in the developing fetus. The female hormones have opposing effects on the brain as testosterone. In neural regions with appropriate receptors, testosterone influences patterns of cell death and survival, neural connectivity and neurochemical composition. In turn, while recognizing post-natal behavior is subject to parenting influences and others, prenatal testosterone may affect play behaviors between males and females, whereas influences on sexual orientation appear to be less dramatic (Hines, 2006).

The question is quite broad and I would start with the cited review articles below, or if need be, the wikipedia page on the Neuroscience of sex differences.

References
- Hines, Eur J Endocrinol (2006); 155: S115-21
- Reinius & Jazin, Molecular Psychiatry (2009); 14: 988–9

AliceD
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    I wonder how the information was gathered in your second paper, and whether extrapolation is acceptable. It appears to have come from dissections of fetal brains. Since no longitudinal follow-up is possible, one can state fact (there was more x here), but extrapolation has to be very, very carefully employed. – anongoodnurse Nov 27 '17 at 17:50
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    Read the Hines abstract (don't have access to full article.) Play behavior does not equal toy preference; play behavior might be grabbing a toy out of someone's hand and hitting them with it vs. sharing vs. other. I suspect this is more in line with what they meant by play behavior than toy preference, unless you have access to the whole article and it addresses toy preference? I'm genuinely curious. – anongoodnurse Nov 27 '17 at 17:53
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    The quoted Wikipedia page, whilst true, does not mention gender bias from adults on how children are treated. Motor skills and language skills are skills which are developed through practise, and especially through practise with an adult. Studies have found profound bias in every aspect of how both men and women play with babies, depending on whether they are told the baby is a boy or a girl - not just in toy choice, but in actively preventing perceived inappropriate toy choice. Most adults in these studies were unaware that they were even exhibiting bias. – Graham Nov 27 '17 at 18:03
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    Dear commenters; the behavioral part is explicitly preceded by a may - it's not a real part of the question and an add-on to the answer; I am deliberately cautious here, because it is indeed difficult to establish causality post-natally. @anongoodnurse I have made the behavioral example more general now - thanks for the watchful eye. Regarding your first comment: the question, the first part of the answer and the paper are all on pre-natal gene expression, so there is no extrapolation necessary? – AliceD Nov 27 '17 at 21:29
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    @AliceD - Yes, (I'm not sure I understand your comment) it is about gene expression. Tracing it back to the source, it's about gene expression in fetal brains. (No longitudinal studies possible.) I do not - absolutely do not - disagree that there are differences between male and female brains prenatally. But what that means is something different. (I UVed your answer before any comments btw.) – anongoodnurse Nov 28 '17 at 00:23
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    @Graham - When my first was born (a boy), I was still a semi-militant feminist, and dressed him in neutral colors for precisely the reason you state: I didn't want strangers/people to act in a particular manner around my son based on sex. I would evade the question. What happened is that people just wouldn't speak to my baby. So after a while, I stopped the experiment, which made strangers much more comfortable. – anongoodnurse Nov 28 '17 at 00:27
  • @Azor-Ahai A few links: A study on perceived crawling ability https://www.ncbi.nlm.nih.gov/pubmed/11063631, a study on perceived crying http://www.psypost.org/2016/06/gender-stereotypes-influence-adults-perceive-babys-cries-study-finds-43541, and a neuroscientist's viewpoint https://jezebel.com/5352031/do-parents-create-gender-differences – Graham Nov 28 '17 at 10:23
  • @Azor-Ahai And most recently, this brilliant BBC documentary. http://www.bbc.co.uk/news/av/magazine-40936719/gender-specific-toys-do-you-stereotype-children – Graham Nov 28 '17 at 10:24
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What about physical differences from birth? Are there differences in size, regions, chemical composition, etc. from birth?

One significant, inherent difference between male and female human brains [from birth & throughout the rest of life] is that male brains are 10-20% larger than female brains.

According to a study performed by the United Medical & Dental College in Karachi, Pakistan:

In this article it is reviewed that how does the brain of a male look and function differently from a female's brain, and what accounts for these differences?

..

Male brains are about 10% larger than female brains and weigh 11-12% more than that of a woman. Men's heads are also about 2% bigger than women's. This is due to the larger physical stature of men. Male's larger muscle mass and larger body size requires more neurons to control them. The brain weight is related to the body weight partly because it increases with increasing height.

..

This difference is also present at birth. A boy's brain is between 12-20% larger than that of a girl. The head circumference of boys is also larger (2%) than that of girls. However, when the size of the brain is compared to body weight at this age, there is almost no difference between boys and girls. So, a girl baby and a boy baby who weigh the same will have similar brain sizes.

To offer more "tangible" figures/values..

  • In 2000, using MRI imaging, Nopoulos, Flaum, O’Leary, and Andreasen measured an average brain volume of 1254 cm³ for men, and 1130 cm³ for women; this is roughly a 10% difference. source

  • In 2004, the University of Pennsylvania Medical Center measured average male brain volume to be 1272 cm³, and for women, 1156 cm³; this is also ~10% difference. source

  • In 2007, the Department of Neurology at the University of California reported an average brain volume of 1363 cm³ for men, and 1188 cm³ for women; again, this is roughly a 14% difference. source

And then, regarding the differences between body size..

  • According to the Center for Diseases Control & Prevention, the average U.S. man weighs 195.7 pounds, while the average woman weighs 168.5 pounds. This is a difference of 27.2 pounds, or, a difference of ~14%. source

Ultimately, the reason for differences in brain size between males & females is still being heavily researched. As mentioned before, one major theory is that differences in brain size can be attributed to differences in body size. Another theory claims the reason is due to how the brain changes size with age, with male brains shrinking more dramatically than females. Regardless of the reason, the fact still remains: male brains are roughly 10-20% larger than female brains.

Additional texts to consider that explore other differences:

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    Surely the trouble with taking a purely scientific approach to intelligence is that it's a pretty poorly-defined concept with no reliable way of accurately measuring? If you want to be rigorous about it, you need to talk about more concrete concepts. – Guy G Nov 27 '17 at 15:55
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    I'm not sure there is any consistent measure of intelligence. I'm also not really sure we need one, I don't think it would help this world. – Tim Nov 27 '17 at 16:43
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    After seeing the reaction that's originated from me including the note about intelligence, I now feel inclined to removed it from my answer, as it's not relevant to the OP, and is a separate topic altogether. This redaction can still be found in a previous version of my response, and in the linked article. –  Nov 27 '17 at 17:02
  • Remember, elephant brains are larger and heavier than humans, but it's neuron density that determines intelligence. Males have large standard deviations in intelligence, and females have small standard deviations. Overall, on average, it all equals out. – Chloe Nov 28 '17 at 04:39
  • @vaxquis I agree that any strong position is unfounded. That's why the most reasonable conclusion is that there are no overall differences, hence why it's unreasonable to claim that the point has been proved (which btw can never happen in science). Lynn is not racist because of his results but because of what he makes of them and what he seems to believe that is not based on research. Read the wiki about him. Furthermore, when his science is motivated by pre-conceived moral judgements, the results have to be questioned. It is no accident that some of his studies contain methodological flaws. – vkehayas Nov 30 '17 at 14:26
  • @vkehayas any study by any scientist can contain metological flaws. In all honesty, as a PhD student, I seldom see articles without them. I'm not willing to discard a study just because it's biased; all studies are biased, because all scientists are human, and all humans are biased one way or the other. OTOH, I'm willing to question it; still, if a see a field with a lot of debatable research going on, I'm willing to say it's probably a debatable matter. Every person who lived with a woman saw those differences; they are better at some things, they are worse at some. (cont) –  Nov 30 '17 at 14:36
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    @vkehayas what interests me here, is what the difference is, why it happens, and can we do something about if, and should we? FWIW, I've removed all my comments, because, as Charles already noticed, they are obsolete after his edit. I reckon this got off-topic enough already. –  Nov 30 '17 at 14:39
  • I intend on leaving my comments here, because there is an implicit assumption in the question that brain size matters for something (c.f. with how interesting the question "Do males have bigger livers than females?" would be and if more than 15,000 people would want to know the answer). This answer was the only one hinting that brain size doesn't matter for much overall, despite the fact that @Charles, perhaps reasonably, took that part out later. – vkehayas Nov 30 '17 at 16:54
  • This is ontologically weird. You are quoting statements that say that per body weight, boys and girls have the same amount of brain; but in your own preface, you write that boys have 20% larger brains. Does not compute. ;) Also, the sentence Male's larger muscle mass and larger body size requires more neurons to control them. seems weird to me, maybe I am missing context. Just because a muscle is larger or a bone is longer does not logically mean that there need to be more nerves. Longer nerves, yes, but without being an expert, that would per se not necessarily change anything in the brain? – AnoE Dec 01 '17 at 10:00
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    @AnoE "You are quoting statements that say that per body weight, boys and girls have the same amount of brain;" -- I think you may have misread the quote.. it says that, specifically at the time of birth, if a male and female baby have the same body weight, they will have negligibly different brain sizes. I don't see there being anything wrong with this statement.. –  Dec 01 '17 at 10:58
  • @AnoE As a male and female humans age, they grow in height; there is a known link between height and brain weight (another common measurement for determining brain size). "Among parameters, the brain weight correlates best with the body surface area, followed by the body height and body weight. The brain weight is related to the body weight partly because it increases with increasing height." See here. –  Dec 01 '17 at 11:01
  • @AnoE And yes, generally speaking, the larger an organism is, the more neurons it needs to control its body; see this publication for more information. "..in order to explain the correlation between brain size and body size, we must fully investigate the web of associations among various biological features in groups of mammals and other animals." .. "therefore that fat and muscle might both scale closely with brain size if metabolic resources are critical." ..Also, see here. –  Dec 01 '17 at 11:14
  • @AnoE Also, see here. "However, large animals need more neurons to represent their own bodies and control specific muscles; thus, relative rather than absolute brain size makes for a ranking of animals that better coincides with the observed complexity of animal behaviour." .. I hope this clears up your concern(s). –  Dec 01 '17 at 11:19
  • @Charles, thank you for the additional information. I was not intending to downplay your answer, just to voice my confusion with the shorter version of it, at that time. I am not the only one, seemingly; the paper you linked has the statement Exactly why this would be the case remains a fundamental question in the study of brain evolution.. I'd suggest that you flesh out the answer a bit and give these kinds of contexts, or else it is mostly useful for people who already knew it or are prepared to follow all the links to study it up on their own. Still, at this moment, your answer... – AnoE Dec 01 '17 at 11:23
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    ... boils down to "males have +14% brain size and +14% body size". In the context of a question about "are male/female brains different from birth" this leads to a wrong conclusion on superficial reading (the conclusion could mistakenly be "yes, males have 14% more brain", while the correct conclusion should be "brain size is directly coupled to body size with neglibly relationship to sex (and by the way, males tend to be 14% larger overall)" - at least considering the references you have given.) – AnoE Dec 01 '17 at 11:25
  • And finally, your links mostly reference comparison of different animals (of different size) like mouse vs. elephant etc.; the question is specifically about humans, i.e., staying within a single species. – AnoE Dec 01 '17 at 11:35
  • @AnoE IMO, the reason(s) behind differences in brain size [between male & female] is a separate question altogether, and, if it were attempted to be addressed as well in this response, perhaps I would get off-topic fairly quickly, since I would then have to talk about muscle mass, metabolic rates, height growth rates, aging w.r.t. neuronal degradation, etc.. –  Dec 01 '17 at 11:35
  • @AnoE Only one of those links addresses animals in general, and I provided that to illustrate a relationship between the body size/muscle mass of the organism and brain size/the necessity for more neurons. Which is to say that, this behavior/correlation is not necessarily unique to humans, but is a general principle that can be applied to most all living creatures with a brain. ... it appears that I accidently provided the same link twice in two different comments, and may be why you think there are multiple links that talk about animals, and not necessarily just humans. –  Dec 01 '17 at 11:39
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One point of view you rarely see is the perspective of sex differences from an evolutionary standpoint. Never mind that this is the reason why the differences exist in the first place if they do at all.

But the short answer is that Human Male and Female brains are unquestionably selected to be different (whether this means they are actually different requires a modern side by side comparison). But to build on this point, think of male and females in terms of evolution. Male and females inherently fill different roles in history and prehistory (If you want to argue that men and women didn't or don't have different roles then show me the man who can give birth to a baby). Given that there were different biological pressures behind the evolution and success of each sex, the brain has been selected (as have other parts of human physiology) to better accommodate the demands of its respective sex as it pertains to one's own reproduction and survival. This much is beyond any reasonable dispute.

Unfortunately this fact cant be used as definitive evidence of sex differences, because even though we can prove that for all of human existence the sexes have done different things what we really need is a side by side comparison of how they are today to come to any conclusion. And given that the current political climate is ridiculously politically correct, it is unlikely any study will be brave enough to publish anything anti PC or else lose funding.

Ref: (Just random references) https://pdfs.semanticscholar.org/4510/e98234d30ea146f523039ba353520a04be3a.pdf

http://www.annualreviews.org/doi/abs/10.1146/annurev.an.15.100186.000325?journalCode=anthro

https://www.eurekalert.org/pub_releases/2015-10/nuos-wam100715.php

https://stanmed.stanford.edu/2017spring/how-mens-and-womens-brains-are-different.html

Edit:

This extension to address '@Elise van Looij' comment that this is a circular argument.

This is history. I have often heard the 'circular argument' position used to try and defend against evolution, aka which came first the chicken or the egg, but it is a logical fallacy. So for the sake of flushing out the position a bit better lets go through the points.

This appears to be a circular argument. Males and females have inherited different roles and therefor they have evolved differently to fill those different roles. How come they 'inherently' have different roles? Because they have evolved that way.

(1) Males and females have inherited different roles? I don't think this is true. Males and females have inherited different potential roles (and maybe an inclination for, or biology best suited for those roles). However no one personally has to fulfill any role. And the roles evolution selects for (namely what is best suited for reproduction) changes over time and between environments. However it is true that those that excel at certain roles best suited for reproduction and survival, will possess traits that will propagate to the larger population by virtue of exponential growth of those genes in the population.

(2) We have evolved differently [solely] because of these roles? No. We have evolved only to reproduce effectively. And this statement isn't limited to just things that reproduce sexually. Biological "roles" are a consequence of the environment. Right now we are still the product of ancient environments because not enough time has passed between then and now for that biological legacy to have been erased. And this is why I put forth the position that the pressures human populations faced for millions(?) of years which unquestionably shaped our biology, can be used in the modern day to make educated hypothesis about our modern (still relatively ancient) physiology.

(3) How come they 'inherently' have different roles? Because in each generation the creatures that did those 'roles' made more babies than the ones that didn't. This is simple math now. 2 A and 2B. 2A reproduce and make 4A. 2B make 1 baby B. Old generation dies, new generation is now 4A 1B. Repeat until B = 0. Now if you want to go all the way back to when there were no roles, you can do that. Go back in history until we reproduced asexually, were hermaphrodites, or no life existed, or some other condition was met. There is no circular-ness in my opinion because you can follow the path back until all starting conditions are different (and thus the circle ends).

But to reiterate the important point because it might be buried in the rest of the text. We have evolved to be a certain way. This way may change in the future and is probably changing right now. But as we exist right now, we are the product of time in the distance past. That passed has shaped us to be a certain way. And we haven't evolved to be radically different from that way yet because not enough time has passed since then for our fundamental makeup to have changed. Think about it; when did the social roles of Male and Female change? 50 years ago? 100 years ago? 1000 years ago? 10,000 years ago? We took millions of years to evolve into this variant of ape that we are. Our ancestral legacy is still strong with us.

But this turned into a discussion of evolution. Instead of what we can learn from evolution. Which was the real purpose of this post.

Tyler S. Loeper
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    Are studies being done, then, and just not being publishing because the results are non-PC? – Jesus is Lord Nov 28 '17 at 22:39
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    In some cases yes, studies are rejected from journals on the basis of not being politically correct. Really this has been a big issue for sometime as it relates to research: 1) https://www.acsh.org/news/2016/08/11/political-correctness-prevents-advancement-of-science 2) https://www.nas.org/articles/Political_Correctness_in_the_Science_Classroom 3) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1299305/ 5) https://scimedskeptic.wordpress.com/2017/03/06/political-correctness-in-science/ 6) https://www.realclearpolitics.com/articles/2014/03/10/science_and_reason_vs_political_correctness_121866.html – Tyler S. Loeper Nov 29 '17 at 14:25
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    This appears to be a circular argument. Males and females have inherited different roles and therefor they have evolved differently to fill those different roles. How come they 'inherently' have different roles? Because they have evolved that way. – Elise van Looij Nov 30 '17 at 11:13
  • See my edit addressing your points. – Tyler S. Loeper Nov 30 '17 at 19:21