Men and women are physically different, a statement that falls easily in the realm of observable knowledge. It takes 46 chromosomes to create a human being—23 from each parent. Two of them determine whether we become men or women—and at least one of them has to be an X (or we die).
We all start life as females for six weeks, then the SRY gene of the Y chromosome develops males. SR is for “sex reversal.” SRY kicks in at week six to cue the formation of testicles. Y can only come from the father. Surely Henry VIII's wives would have loved to know that data point, even as it's rather doubtful the King would have beheaded himself. Goes to show how we often learn vital information too late in the assumption game.
Another curious data point is that inequality starts at chromosome level—the X chromosome carries around 1,500 genes and they do most of the heavy lifting in embryo development. While the Y chromosome is down to less than 100 genes and has been shedding them at the rate of 5 every 1 million years.
In Brain Rules John Medina says since females carry two X chromosomes, they have double the necessary amount. Thus the embryo simply ignores one of them, a tactic that continues to work to this day. It's not a systematic cut of one set—the embryo picks and chooses from the pool provided by both parents. Hence why sisters may be so different from each other.
Males however need all of their 1,500 genes (which come from their mother) to survive, plus the SRY genes. X genes govern how we think—a large percentage of them are involved in the creation of the protein that builds the brain. “Researchers call the X chromosome the cognitive hot spot,” says Medina. Genes are mediators of cell functions and collections of these cells form brain structures.
There's no question that women are genetically more complex.
How male and female brains differ
Just like the physical appearances of men and women—and though this is a meta-pattern that replicates at individual levels, there are person to person nuances, as we should expect.
When it comes to neuranatomy, the real challenge is finding areas that aren't affected by sex chromosomes. You can see differences in the cortex, the amygdala, even the biochemicals that brain cells use to communicate with each other.
Researchers from the University of Pennsylvania conducted a study# of about 1,000 brain scans and found that male and female brains are wired differently. The scans showed few differences in connectivity up to the age of 13, but became more differentiated in 14- to 17-year-olds.
There's greater connectivity between women's left and right sides of the brain—women have 10 times more white matter, responsible for faster connections. In their brains neurons are also closer together, another data point in favor of speed.
Some women even have as many as 12 percent more neurons than men do. They are mostly found in the layers of the cortex responsible for signals coming in and out of the brain. Psychologist Sandra Witelson says this may be one reason why women tend to score higher on tests that involve language and communication.
The connections in men are mostly within each hemispheres with the exception of one area—the cerebellum, which plays a vital role in motor control. Men also have approximately 6.5 times more gray matter, full of active neurons.
As for the differences in brain structure, Medina says scientific labs have found that certain parts of the cortex is thicker in women than in men. The front and prefrontal cortex control the majority of our decision-making ability. The limbic system where we find the amygdala controls the generation of emotions and the ability to remember them—this region is larger in men.
Men can produce serotonin 52 percent faster than women. This is the biochemical that regulates emotion and mood. Scientists don't know if this makes a difference. They do know that the response to stress is different—women's left hemisphere's amygdala activates, which is responsible for remembering emotional details. In men it's the right hemisphere's amygdala that lights up, which gives a gist of what's going on.
Genetics account for some structural differences. But we know from neurological development that all human beings inherited the homo sapiens genes (homo includes Neanderthals), which we share with some of the smartest people who ever lived. At the time of birth we have the same potential as Leonardo da Vinci.
How our environment influences us
From anthropological research and observation we know that our environments plays a key role in our development. Humans are born before being fully developed. The reason is our brain would become too large for the birth canal. So we rely heavily on our environment as the context that guides our growth.
Studies have found that when the ground is not safe to put babies onto, for example in the jungle, they learn to walk later. But not only that. The marvel that we hold in our skull is cross-networked, which means that when one function in the brain grows, the whole brain capacity expands.
Mobility builds our lung capacity and it in turns feeds the brain where synapses fire to help us do many other things. Visual competency helps us distinguish between light and dark and then from outlines we see details until at some point we can see big words. Growth here also expands our abilities.
When we're safe and our needs are attended to, we begin to explore what is around us using vision, auditory, and tactile sensation to both communicate and interact with our environment. We learn “this is how it feels to roll over or move” when we see something different in our immediate field of vision, and “this is what happens when I move arms and legs,” as our visual clues let us discover.
If we grow up in a house full of books, and our guardians or parents facilitate our path to them through reading and teaching us how to read, we learn to appreciate that reading opens our door to new worlds. It's the same with music and auditory refinement. The same with mobility and sports.
It's an equal opportunity that depends on two factors—the ability to explore safely with degrees of support, and also the specific self-interest of the individual child. Siblings who grow up in the same house do have a different genetic makeup—females select from each parent's set—and a different environment—older siblings have younger siblings, may go to different schools, and so on.
What about mobility? How can we tell if a child will become a great athlete? We can help to a certain extent says David Epstein in The Sports Gene. And yes, there differences in athletic performance between men and women. Even factoring in predisposition and opportunity, we're built differently. In week six, SRY cues the formation of testicles inside which are the Leydic cells—they synthesize testosterone.
In turn it drives the development of longer forearm—male athletes can throw three standard deviations faster than women, “about twice as large as the male/female disparity in height.” Boys are also more skilled at tracking and intercepting flying objects, a direct result to exposure to testosterone in the womb:
“In the long jump, women are 19 percent behind men. The smallest gap occurs in distance swimming races. In the 800-meter freestyle, top women are within 6 percent of top men.”
This even taking into account a large disparity in the type of environment men and women were immersed in:
“In the first half of the twentieth century, cultural norms and pseudoscience severely limited women's opportunities for athletic participation. At the 1928 Olympics in Amsterdam, the media account (which was fabricated) of exhausted female competitors lying on the ground after the 800-meter race was so distasteful to some doctors and sports writers that the event was deemed hazardous to female health.”
The New York Times headline read—“This distance makes too great a call on feminine strength.” The consequence was a banning of all women events longer than 200 meters from the Games for the next 32 years.
How culture determines opportunity
It was worth a small detour into athletic performance to bring up the question of culture. Aristotle is typically quoted among the great ones. What he said in this case is illuminating of the times:
“The female is an impotent male, incapable of making semen because of the coldness of her nature. We therefore should look upon the female state as if it were a deformity, though one that occurs in the ordinary state of nature.”
Except of course that without women we would have no mothers… or life. That pesky X chromosome everyone needs.
The differences in the structure of male and female brains account for the propensity to do certain things better. As we said above, women are better communicators, they process information at greater speed, remember details about emotional experiences—more data points and greater resolution.
Women recover verbal impairment from strokes more quickly. They also cement relationships with their group by maintaining eye contact when they communicate.
Men get the gist of things, use verbal skills to negotiate their status in a large group, and tend to withdraw under stress. They see the world as a hierarchy and prefer a very direct approach to communication. Asking, “would you like to get a drink?” when we're thirsty may backfire. A better option would be to say, “I'm thirsty, let's stop here and get a drink.”
Culture is the biggest and most persistent environment we have. It has a strong role in influencing how we make decisions. We have a personal culture, a family culture, a local community culture, a culture at work, in our region, in our country, nation, age, and so on. Brain biology and genetics also influence us.
Behavior drives performance but is in turn driven by input—how we treat one another, the demands placed on us, inform what we learn and our development. Social forces are part of the mix. Cultural norms may dictate what we want to see or hear. An Italian proverb says, “there's no worst deaf than the one who doesn't want to hear.” It rings wise, pardon the pun.
We need some caution also to navigate the right and left brain distinctions. Renowned psychiatrist and writer Iain McGilchrist says the divided nature of our brain has profoundly altered human behavior, culture, and society. In The Master and His Emissary, he says we now know that every type of function —including reason, emotion, language, and imagery— is subserved not by one hemisphere alone, but by both.
The physical organ we call brain is different in men and women. What we do with it depends on a number of factors, including health, opportunity, desire, and social norms. Because it is so hard to isolate people from the context of their lives, scientists and research are still largely inconclusive as to the consequences of the brain's physical differences, though they won't stop trying.
By definition, every theory we formulate is a calling card for setting out to prove it—to explain a group of facts, which we manufacture (for the Latin root). We also use hypotheses as tentative explanations for an observation, phenomenon, or scientific problem to test and investigate. How often do we look to disprove our theory or hypothesis?
My empathy levels are fine, but it's the systems-thinking that gets me going. There's much more to say about this fascinating topic and applications. To get to better answers, we should have smarter aims. It starts with asking better questions.