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"The five missing ounces of the female brain"[1] is a widespread term brought about in the Victorian Era, and, though you may think that was long time ago, the concept still has a vicious grip on people's perceptions of neurobiological sex differences.
In the 19th century France, Paul Broca established that this difference in size may be proportional to a difference in intelligence: 'There is a remarkable relationship between the development of intelligence and the volume of the brain' [2].
This paradigm set off a century of misleading methods. Brain size was assumed to be relevant, and so they used craniology to ascertain elements of cognition.
Such ambiguous methods were used until the late 20th century, and lo and behold! — the invention of Magnetic Resonance Imaging.
Nowadays, some stubborn researchers just can't leave this matter alone, hence the birth of the Gurian approach.
“Boys come out of the womb with a formatting for non-verbal, spatial, kinesthetic activity on the right side of the brain. In the areas where girls’ brains come out ready to use words, boys’ brains
come out ready to move around, kick and jump.” [3]
Entitled psychologist Michael Gurian blames testosterone, and established neuroscientists blame
him.
You should now be able to recognize a pattern: monkey see, monkey do.
The simple patenting of his theory influenced decades of research.
It was deemed most relevant, and so many decades were wasted testing for relevant testosterone levels (amniotic or maternal) [4], and even a measurement of index and ring finger length was used as a marker (2D:4D Ratio) [5].
Though these tests were accurate enough for ascertaining testosterone levels, scientists soon thought that maybe they should consider the brain a reputable subject for studying neurobiological dimorphism.
So, luckily, because it took them so many decades, by then MRIs had been invented!
By now it must be clear that every study should be taken with a grain of salt, and in aid of that comes p [6]. Statistically, it was established that 1 in 20 reported differences occur by chance. Since sex is a naturally occurring, routinely phenomenon, the disparities discovered end up being documented more than the lack thereof, with the latter outnumbering the former.
And yes, although Paul Broca was a regular customer of Republican Beliefs Cafe, he was right about one thing. The female brain is significantly smaller than the male one. Where he went
wrong was presuming it was relevant.
The difference in brain size occurs as a consequence of the difference in body size. But of course, this "male brain ... predominantly hard wired for understanding and building systems" [7] also requires different pathways, connections, velocities. All of these, though, garner the same result and no behavioral or cognitive effects.
Other structural differences have been found, but researchers struggle to validate the relevance of
these discoveries.
One large study describes that men have more connections intrahemispherically, or front to back, while women's left to right connectivity has proven to be better, opposite in cerebellar
connections [8].
Usually, in consequence of structural findings, researchers grapple to make cognitive sense of them, so, in support of McGlone's theory that men's brains are more lateralized [9], which makes for better specialized skills [10], they concluded that men have enriched connections between
perception and coordinated action, while women are simultaneously intuitive and analytical thinkers.
This aspect is apparent only in subjects of adolescent age, which suggests a hormonal surge as the culprit, as it's entirely nonexistent in other age groups [8].
Another theory is that, seeing as these findings don't translate to anything more than a blob on an MRI, rather than being influenced by hormones, they may exist as they do because of environmental and social factors.
One study certainly suggests so.
Ilan Dar-Nimrod and Steven Heine found that scientific language majorly influences people's perception [11]. In this case, the use of neuroscientific jargon resulted in major susceptibility to self-stereotyping; this would prove that environmental and social factors affect identity
considerably, which in turn may apply to brain structure.
After reading an article about how men are better genetically endowed for mathematics, girls performed significantly worse on GRE tests [11].
All in all, any differences found are not qualitatively reliable, as they appear one way in a study, differently in another one. Differences that are documented consistently enough are not relevant
quantitatively, as the difference found between sexes is around 1%: the amygdala, bigger in men [12].
If found to be psychologically relevant, this concept may debunk centuries of women being pegged as 'born caregivers, naturally emotional' [13], as the amygdala is the site of social emotional behavior.
Cordelia Fine coined the term 'neurofeminism' in her 2010 book Delusions of Gender.
Though it quickly gathered the public's interest, it is understandable if you choose to be agnostic about believing in this relatively new concept.
The brain is the headquarters of mystery, but, as far as gender disparities are concerned, we seem to finally be on the right track.
Hopefully, soon enough, that train will raid the zoo just a little less often (are animals viable subjects for human studies?)!
Bibliography:
1. Charles Darwin (1871) The Descent of Man, chapter 8.
2. Stephen Jay Gould (1981) The Mismeasure of Man, pg. 83.
3. Michael Gurian & Kathy Stevens (2006) How are the boys doing?, pg. 87-93.
4. Baron Cohen (2002) The extreme male brain theory of autism.
5. Swaab DF, Chung WC, Kruijver FP, Hofman MA, Hestiantoro A. Sex differences in the
hypothalamus in the different stages of human life, S1-S19.
6. Beltz AM, Beery AK, and Becker JB. Analysis of sex differences in pre-clinical and
clinical data sets.
7. S. Baron-Cohen (2003) They just can’t help it, The Guardian.
8. Marco Hirnstein, Kenneth Hugdahl & Markus Hausmann (2019) Cognitive sex
differences and hemispheric asymmetry: A critical review of 40 years of research,
Laterality, 24:2, 204-252
9. McGlone, J. (1980). Sex differences in human brain asymmetry: A critical survey.
Behavioral and Brain Sciences, 3(2), 215–263.
10. Baron-Cohen, The Essential Difference: the male and female brain, p. 1 (2003).
11. Dar-Nimrod I, Heine SJ. Exposure to scientific theories affects women’s math
performance. Science. 2006 Oct.
12. Marwha, D., Halari, M., & Eliot, L. (2017). Meta-analysis reveals a lack of sexual
dimorphism in human amygdala volume. NeuroImage, 147, 282-294.
13. Baron-Cohen, The Essential Difference: the male and female brain, p. 185 (2003).
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