Science and sociology: The two fields often find themselves at loggerheads. That is the case with ADHD. And, it’s increasingly the case when it comes to accepting that there are differences between the male and female brain.
Personally, I’m siding with science. Perhaps after you read a sampling of staggering statistics below—continued fully in the next post—you will, too.
But first, a bit of stage-setting.
In social media and elsewhere, sociological theory threatens to crowd out scientific facts. The sociological theories seem “intuitive,” therefore alluring. Intuition may be quick and easy. The human brain generally doesn’t like to think; it’s too hard! All the same, intuition is not proof.
Many sociologists and social psychologists have long issued intuitively inviting claims about ADHD. They call it a “social construct.” The implication is that ADHD is an invention of social norms—or Big Pharma. Unfortunately, sociology is not a life-science field.
To these sociologists and social psychologists, I ask, “Are eyeglasses the product of social norms, too? Would the vision of people prescribed eyeglasses be just fine if they didn’t want to read, drive, create, and not walk into walls? Should we all just go back to the good ol’ pre-Guttenberg Press days?” I would also refer them to my four-part series: Eyeglasses, ADHD, and Stigma
This post attempts to address—in a tiny and gingerly way—another claim made by the non-scientifically inclined: There is little difference between the male and female brains; the differences largely spring from culture.
This complex topic evokes strong feelings. We cannot bring a binary mindset to exploring the topic of male-female biological differentiation. Human brains are like snowflakes: No two are alike. But it’s a topic worth exploring. Brains drive both physiology and behavior.
Please consider this a short blog post meant to spark thought—not a comprehensive treatise. As always, I welcome your thoughts.
Sex Begins in the Womb
The so-called Decade of the Brain, the 1990s, brought us revolutionary brain-imaging technology. This technology made possible the unprecedently precise study of the human brain. The evidence has been mounting ever since, and it points to inherent differences in how men’s and women’s brains are “wired” and how they work.
Add this to what we’ve known it for years: All humans develop from the same starting point in utero.
Yet—and this is critically important— that ends at about 6-9 weeks. That’s when fetuses with a Y chromosome start developing male sex characteristics in the brain and genitalia.
Excerpt from Sex Begins in the Womb (U.S. Institute of Medicine US, 2001):
During early development the gonads of the fetus remain undifferentiated; that is, all fetal genitalia are the same and are phenotypically female.
After approximately 6 to 7 weeks of gestation, however, the expression of a gene on the Y chromosome induces changes that result in the development of the testes. Thus, this gene is singularly important in inducing testis development.
The production of testosterone at about 9 weeks of gestation results in the development of the reproductive tract and the masculinization (the normal development of male sex characteristics) of the brain and genitalia.
In contrast to the role of the fetal testis in the differentiation of a male genital tract and external genitalia in utero, fetal ovarian secretions are not required for female sex differentiation. As these details point out, the basic differences between the sexes begin in the womb
Now for a caution: Nothing about fetal development is straightforward or binary. That’s human biology for you. External influences can interfere with all aspects of fetal development—for example, nutritional deficiencies or toxins, the mother’s stress, illness, or trauma.
In other words, the full expression of inborn genetic programming is not clearcut; it depends upon the full range of environmental factors. Yes, that includes culture—but also includes much more than culture. That’s true from conception to death.
Consider a Brief Example: Autism
Autism spectrum disorder (ASD) is 2 to 5 times more common in male individuals than in female individuals. That’s a very clear difference.
No doubt many girls with ASD go undiagnosed, but there’s no evidence that contributes to this disparity. There is evidence, however, of structural brain differences between male and female study subjects—and between female controls and females with ASD. In fact, some research has shown that the brains of girls with ASD more resemble male brains than female brains.
Consider this 2017 study in JAMA Psychiatry: Association Between the Probability of Autism Spectrum Disorder and Normative Sex-Related Phenotypic Diversity in Brain Structure.
Researchers imaged the brains of 98 individuals ages 8 to 22 with autism spectrum disorder and 98 control subjects. Each group contained roughly equal numbers of male and female subjects. Confirming earlier research, the found that the pattern of variation in the thickness of the brain’s cortex differed between males and females in the control group. But the team also found that the great majority of female subjects with ASD had cortical-thickness variation profiles similar to those of typical non-ASD males.
(What is cortical-thickness? It is the outer layer of the cerebrum, or the cerebral cortex; it is composed of folded gray matter and thought to play an important role in consciousness and intellectual ability. For more info: Associations between cortical thickness and general intelligence in children, adolescents and young adults)
Did you get that? Having a typical male brain structure, whether you’re a boy or a girl, substantially increases the risk for ASD. Obviously, more boys than girls have this brain profile. That likely explains ASD’s two- to fivefold preponderance among boys compared with girls. It’s not culture; it’s the brain structure and function.
Autism and the Empathy-Systems Polarity
While we’re on the topic of autism. Autism researcher Simon Baron-Cohen has called autism “extreme male syndrome”.
In 2004, I was greatly impressed by his book, The Essential Difference: Male And Female Brains And The Truth About Autism. He details his research linking fetal androgens (testosterone) with autism. These hormones can be both endogenous and exogenous— that is, issuing from the fetus or from the uterine environment.
(When I read that previous inhabitants of that uterus can leave their own hormonal mark for future occupants, I thought about my siblings. What else besides coats and old schoolbooks did those three brothers and three sisters pass down to me?)
He also explains his rationale for what he calls the “systems-empathy” polarity. One end of the spectrum is empathy, and the other end is systems. (Systems is, simply put, the drive to analyze and construct systems that follow rules; think math, science, finance, engineering).
Based on his research, Baron-Cohen maintains women are generally higher in empathy and men generally higher in systems. That is a brain-based difference.
Again, this is a spectrum. There are many men with higher empathy than systems ability, just as there are many women with higher systems ability than empathy. Think of it as being similar to height; men as a group are taller than women as a group, but some women are taller than some men.
Now for The List: For Every 100 Girls…
To be clear: Human sexual differentiation is not binary; it is also a spectrum. For purposes of research, though, large numbers indicate differences between the general groups of male and female.
Which brings us to the staggering list of statistics.
Tom Mortenson first compiled this list in 2006. .He gave me permission to share the most current version with you.
Mortenson is currently a Senior Scholar at the Pell Institute for the Study of Opportunity in Higher Education in Washington, D.C. and an independent higher education policy analyst. In 2003, he wrote a fact sheet: What’s Wrong with the Guys?
The next post will include Mortenson’s entire list, with charts.
Birth and Death: Male Versus Female
Some bullet-point statistics below clearly document the physiological and behavioral differences between male and female, because they manifest at birth.
Others likely have a cultural overlay. Teasing out which comes first should be grounded in careful thought and study, not preconceived ideology or intuition.
Research by Russell Barkley et al shows that untreated or poorly managed ADHD is associated with premature death. The brain is obviously driving behavior.
Let’s start with birth statistics that point to greater male mortality:
- For every 100 girl babies that are born alive, 105 boy babies are born alive.
- For every 100 girl babies born dead, 106 boy babies are born dead.
- For every 100 girl babies that die in the first 28 days of life, 117 boy babies die in the first 28 days of life.
- For every 100 girl babies that die after the first 28 days of life but before they reach their first birthday, 124 boy babies die.
Mortality and suicide from childhood into young adulthood:
- For every 100 girls ages 1 to 4 years that die, 125 boys the same age die.
- For every 100 girls ages 5 to 9 years that die, 123 boys die.
- For every 100 girls ages 5 to 14 that commit suicide, 225 boys kill themselves.
- For every 100 girls ages 15 to 24 that commit suicide, 433 boys commit suicide.
The disparate effect crosses ethnic boundaries, too:
- For every 100 white, non-Hispanic girls ages 15 to 19 that die, 216 white, non-Hispanic boys the same age die.
- For every 100 black girls ages 15 to 19 that die, 310 black boys the same age die.
- For every 100 Asian girls ages 15 to 19 that die, 203 Asian boys the same age die.
- For every 100 American Indian girls ages 15 to 19 that die, 180 American Indian boys die.
- For every 100 Hispanic girls ages 15 to 19 that die, 287 Hispanic boys ages 15 to 19 die.
Statistics based on data from 2011, the source is the U.S. National Center for Education Statistics.
Look to my next post for the full list.
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