Thoughts on Brain Size, Birth, and the Ignorance of Obscene Wealth

2025 is going to be a bumpy ride

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I’ve been trying to come up with a way to begin to discuss what 2025 might mean for women’s health here in the United States, and a tweet from Elon Musk with childish logic about brain size and birth has unintentionally provided a window. As Musk is closely enmeshed with Trump and his cronies, sadly, what he says bears discussing, especially as it’s probably in line with many of the tech dude-bros who, according to the New York Times, are all “over the transition, shaping hiring decisions and even conducting interviews for senior-level jobs.”

Sigh.

To lessen the pain of discussing Musk, I’d also like to discuss the original study that spawned his inane tweet. It is about dementia and is actually interesting. However, the conclusions are useless to Silicon Valley as there is nothing to monetize.

Here is the tweet in question. I am not on Twitter anymore (I’m not calling it X), but it was circulating on BlueSky and Threads and was sent to me via several direct messages, crossing my threshold for discussion. So here we are!

And yes, it’s a normal response to recoil from reading a tweet from Musk about the “birth canal.”

I made a half-hearted attempt to look for the tweet personally, but Musk’s feculent firehose was more than I could bear. Leaving Twitter was a fantastic decision; if you are still there, I recommend you stop contributing. The sheer volume of Musk’s tweets left me wondering how he had time to sleep, run companies, and become the world's number one “Diablo 4” player. But the thought quickly passed because I don’t care to expend any more energy than necessary thinking about him. Fortunately for me, several brave souls over on BlueSky verified the tweet.

His tweet gives off both master race and scientific ignorance vibes, which is totally on brand for the Trump Project 2025 agenda for women’s health because what are women anyway? Breeders for the “right” kind of babies, that’s what.

Here’s the tweet to which Musk was replying:

The original post references a pre-print (so not peer-reviewed data) from January 2023) called “Secular Trends in Head Size and Cerebral Volumes In the Framingham Heart Study for Birth Years 1902-1985.” The conclusion (for those of us who bothered to read it) is that brain volume has increased over the birth years from 1902 to 1985, likely due to “improved early life environmental influences over ensuing decades.” The pre-print doesn’t even mention c-sections and has nothing to do with birth.

It’s worth noting that the actual paper has been published (March 2024) and is called “Trends in Intracranial and Cerebral Volumes of Framingham Heart Study Participants Born 1930 to 1970.” It’s a cross-sectional study that looks at changes in brain volume over time as a potential contributor to declining rates of dementia. The cognitive reserve hypothesis suggests that a larger brain volume is protective against dementia; essentially, a larger brain can tolerate more loss. This is also one theory of why exercise is protective against dementia because exercise is also linked with larger brain volumes.

This study found that the brains of people born in the 1970s were about 6.6% bigger than those born in the 1930s. (People born in the 1970s were also 1.6 inches taller, and as brain volume is linked with a person’s size, the researchers controlled for this confounder). The conclusion was that, almost certainly, a complex mix of factors that a person is exposed to over their lifetime, like their health, nutrition, education, and how they are treated by society, creates an environment that allows for greater brain growth. Not cesarean sections, but the environment. This is not a surprising conclusion as the average age of the first MRI in the study was 57.7 years, so linking any change in brain size at age 57 back to birth would be ludicrous.

It’s always amazing (ok, not really) how so many studies about health hark back to the basics. It’s almost as if everyone has enough nutritious food, exercise, sleep, and good health care that we might all be a little healthier. But hey, more c-sections, amirite?

(As an aside, this is one of the reasons I get so infuriated by so-called functional medicine and hypocrites like Robert F. Kennedy Jr. They falsely complain that all science-based medicine wants is Big Pharma, and yet here is paper #234,678 discussing the importance of social determinants of health. Excuse me while I scream into the void).

Size Doesn’t Matter

There are probably a lot of people who mistake brain size as a marker for intelligence; after all, we live in a “size matters” kind of society, but someone who runs a company dedicated to unlocking the potential of the brain, like say, Neuralink, should have this basic knowledge or at least have access to people who have this knowledge.

While it’s true that the birth canal does put a limit on the size of the fetal head, it doesn’t necessarily follow that taking away the size of the birth canal by universal c-sections would unleash a bigger human brain, as there are many factors contribute to the size of the fetal brain. In addition, there are neonatal health ramifications with very high rates of cesarean delivery, never mind the fact that in the United States, less than 50% of women have paid maternity leave.

In Brazil, in a recent study, the cesarean section rate is 55.5% overall, but there is a big difference by socioeconomic group, and the rate was 79.7% among those with the highest level of education. An unintended consequence for this group is a high rate of early-term births, meaning delivery between 37 and 39 weeks, likely the result, at least in part, of attempting to perform the cesarean section before labor. Non-medically indicated births between 37 and 39 weeks have health ramifications for the infant, including a higher rate of respiratory distress syndrome, pneumonia, respiratory failure, and admission to the neonatal intensive care unit.

Regardless of the broader medical and societal implications of the c-section tweet, there is a lot of research that shows brain size is not linked with intelligence. Even more interesting, over the past 100,000 or so years, the size of human brains has decreased (it’s fascinating work, and you can read a summary here). And while I don’t like to rest on anecdotes, sometimes they help make a broader point. Sir Isaac Newton was tiny at birth, either due to being low birth weight or premature or both, and was not expected to survive…and yet he became one of the greatest scientific minds of all time (something I personally found very comforting as a parent of two low birth weight, extremely premature infants). And if I remembered more calculus, which Newton invented, I could probably make a semi-witty joke about being mindful of preconceived notions about limits and value.

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Men’s brains are, on average, 11% larger in volume than women, so you can see how misogynists would be enthralled with the idea of larger brains being linked to intelligence. There is a significant overlap in brain size between women and men, so brain volume is not a dimorphic trait, and consequently, not all men have larger brains than women. The difference in brain size between men and women is primarily related to men being, on average, heavier and taller. Interestingly, the average differences in brain volume by sex between men and women are less than for other organs as, on average, male hearts are 17% larger and lungs are 23% larger.

Scientific Ignorance and Misogyny Go Hand in Hand

I’m not surprised that Musk has some imagined special knowledge about the physiology of birth. I agree with Paul Krugman, who wrote recently in his Substack that the wealthy and powerful, like Elon Musk, “are often far more ignorant than policy wonks can easily imagine.” What could we experts know? After all, we are not billionaires! Then again, accepting that experts have the expertise requires billionaires to entertain that they aren’t the living God their sycophants proclaim.

I am confident this is not the last weird, creepy tweet that we’ll see about reproduction. We’ll also see more demonizing of contraception and abortion on social media. It will be interesting to see those from Silicon Valley who publicly embrace eugenics go head-to-head with the radical Evangelical forced birthers, whose rallying cry is every blastocyst is sacred. Make no mistake about it; their goals are the same: establishment of White Nationalism, which includes the subjugation of women, but they are going to bash heads over assisted reproductive technologies and egos. They’re all fucking hypocrites, so I’m sure they’ll figure it out, but we can only hope their incompetence slows them down.

And so I suspect 2025 will bring us many men and a few women, promoting scientific ignorance (and misogyny) masquerading as confidence, and given that a lot of people have chosen to bend the knee, it’s going to be increasingly hard to distinguish the science from the slop in this dystopian agenda, but I’ll be here doing my best to help.

References

Secular Trends in Head Size and Cerebral Volumes In the Framingham Heart Study for Birth Years 1902-1985, Preprint. https://www.researchsquare.com/article/rs-2524684/v1

DeCarli C, Maillard P, Pase MP, et al. Trends in Intracranial and Cerebral Volumes of Framingham Heart Study Participants Born 1930 to 1970. JAMA Neurol. 2024;81(5):471–480. doi:10.1001/jamaneurol.2024.0469

Barros FC, Rabello Neto DDL, Villar J, et al. Caesarean sections and the prevalence of preterm and early-term births in Brazil: secondary analyses of national birth registrationBMJ Open 2018;8:e021538. doi: 10.1136/bmjopen-2018-021538

Avoidance of nonmedically indicated early-term deliveries and associated neonatal morbidities. ACOG Committee Opinion No. 765. American College of Obstetricians and Gynecologists. Obstet Gynecol 2019;133:e156–63.

Lise Eliot, Adnan Ahmed, Hiba Khan, Julie Patel. Dump the 'dimorphism': Comprehensive synthesis of human brain studies reveals few male-female differences beyond size. Neuroscience & Biobehavioral Reviews, 2021; 125: 667 DOI: 10.1016/j.neubiorev.2021.02.026