Image by The Conversation
“On the basis of the information
available it seems unrealistic to deny any longer the existence of male and
female brain differences.”
--Richard
Restak, The Brain: The Last Frontier (1979)
In the late 1970s, neuroscience investigator Richard Restak
was excoriated as a sexist for suggesting—based on evidence, that is, expert
opinion—that the brains of human males and females are different. To hold this opinion is to risk accusations
of neurosexism. However, for “gender justice” advocates, female (but not male)
brain differences are now insisted on.
This advocacy is mobilized in order to distinguish uniquely women’s
issues as the platform for rights and protections, including diversity, health,
social, and psychological.
Ongoing studies show a mosaic of male and female features in
virtually every brain; there is no pure male or female exhibit. Yet certain structures and chemistry occur more
commonly in each gender. Male and female
brains show bias in a continuum across a number of aspects, from drug
processing to reasoning style, mental states to mental disorders.
One of the reasons brain-sex dimorphism is controversial, Restak
explains, is that sex identity and behavior in our species aren’t neatly
compartmentalized as in other research subjects like mice and monkeys. Many question whether animal studies are
analogous to studies of brains in primates.
In humans, genotypic sex, phenotypic sex, sex attraction, and gender
identity are not reliably aligned. Sex
organs and hormone effects are visible evidence markers between the sexes. However,
these are aligned by genes and their expression throughout the body, like testosterone
(male) and estrogen (female) hormones, influencing thinking and behavior in the
brain. These include connections
happening prenatally, before exposure to cultural or environmental experience. The female brain is the default through the X
chromosome, meaning that every brain begins as female but only half develop as
male.
Stepping outside the research lab, what is the first thing
you notice when meeting a new person?
The only biological difference between people isn’t race, class, or age. It is gender.
We depend on gender knowledge to adjust our communication style to suit male
or female. Gender is embedded in our DNA
as chromosomes XY or XX. No matter how gender is expressed or repressed within
cultural norms (epigenetics), these genes wire our secondary physical
expression as breast size, genitalia, height, weight, muscle size, hip width, sex
drive, voice pitch, facial features, and pubic hair. Unsurprisingly, gender also sets up the male
and female brain in distinctive ways.
Whatever gender persona you might decide to exude, your DNA doesn’t migrate
between the two gender codes, XX and XY.
Sex hormones are important to the way people look, feel, and
behave. In men, the Y chromosome
carries a protein promoting testes formation, testosterone production, and
creation of the male brain. While this
protein makes males more prone to retardation and learning / speech disorders,
dyslexia, and autism, males also make up the majority of geniuses at the opposite
end of the intelligence scale. Female
fetuses are better able than male to recover from prebirth brain damage.
Estrogen in women encodes language as spoken sounds
(phonemes) as well as the visual coding of written language, and also plays a
role in long-term memory (so women are slower to forgive and forget than men). Testosterone predisposes males to risk danger
and aggression, so that most murderers are male. The male hormone sets desire in men, but testosterone
also drives sexual desire in women, even with far less of it in the female brain
mix.
Whatever the differences, Restak concludes, “it helps to
keep in mind that such differences do not imply that one sex is superior to the
other” (Mysteries of the Mind, 2000, p. 64). Only that each has a likely inbuilt bias to
prefer one type of thinking or acting over others—and therefore, to practice and
excel at that behavior. An article on The
Conversation site ventures that “On the other extreme, we are dismissed
by women’s health advocates, who believe research has overlooked
women’s brains – and that neuroscientists should intensify our search for sex
differences to better treat female-dominant disorders, such as depression
and Alzheimer’s disease” (April 22, 2021).
For example, women perform better than men on verbal tasks
(estrogen-promoted), as well as intuitive reasoning, motor skills, and scanning
environments for select features (finding all the green chairs in a mostly blue
auditorium, or the best fruits on the tree, or a child on a bustling playground). The hippocampus, the human memory center, is
larger in females, with a higher density of neural connections. It facilitates memory for people and reading
their emotions.
Men excel at spatial tasks, including rotation of objects in
mental space, and do better at math, logical reasoning, and motor skills
directed at distant targets (aiming and tracking). Men in mazes navigate by dead reckoning,
while women rely on landmarks sequenced in memory. This is why men generally ask
for directions much later than women. This is the root of the difference
between hunters and gatherers, and why hunter-gatherer societies were based on
gendered division of labor.
Another sex-brain disposition is in the anatomical balance
of gray and white matter—women have more grey (the core of nerve cell bodies)
while men have more white matter (nerve fibers for signaling around the nervous
system) involved in connecting brain and body.
Female brains show increased coordination between regions, whereas males
have a more separated left-right structure and connect back to front versus
women’s hemispheric coordination left to right.
Men and women process neurochemicals differently using different
receptors, as for example serotonin synthesis, seen in dominant primates, is
over 50% higher in males.
Experience and attitude influence brain dynamics and the development
of structure and function. Lived
experience, for example, education, can establish new circuits and outputs, facilitating
the hardwiring of the brain. Upbringing and culture can activate or repress
brain functions and their genetics, creating new nerve cells and connections,
the essence of neuroplasticity. Adaptability through specific action and
memory is our species’ main strength: the ability to connect our biology to our
cultural learning by brain growth. The human ability is to adapt to new
circumstances over generations, as well as from moment to moment to meet needs
and build opportunities.
The question now arises: How do
we know these abilities and their sex DNA are not simply cultural rather than
hormonal, as in biodeterminism? For example, Jews make up 2.4% of the US
population, but 35% of US Nobel prize winners. Is this nature, or nurture? The simple response is that culture tends to
follow rather than determine biology, reinforcing rather than forcing brain bias.
In the Jewish case, this bias is an environment of reward for literacy, encouraging
questioning to find answers. Culture is
built on the existing body and brain, but then determines how they work within
the process of cultural values and conditioning—for instance, in the way we
think about and recognize gender. This
bio-cultural feedback loop is our uniquely human heritage.
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Thanks to Dr. Herb Adler for consulting
on this topic.
