The Science of Sex Differences

August 27, 2013 | 6 comments

More and more people in our nation today think that sex (that is, maleness and femaleness) is not an objective biological reality but rather a social construct. Accordingly, instead of "sex" they prefer to use the word "gender"—a word that, until late last century, referred exclusively to language (most languages apart from English assign male, female, or neuter genders to nouns). Unlike sex, gender can be manipulated to serve cultural preferences.

Though there are a variety of ways to respond to this nonsense (how's that for tipping my hand?), in this post I would like to respond with some findings of modern science.

Those who reject the objectivity of sex will often say that although male and female bodies may have some differences between them, our brains are just the same. One man, who is currently raising three "genderless children," argued, "If you really want to get to know someone, you don’t ask what’s between their legs."

But is the only difference between men and women "what's between their legs"?

Brain Differences

As it turns out, male and female brains are biologically different.

in 2004, an all-star team of fourteen neuroscientists, from the University of California, the University of Michigan, and Stanford University, published findings showing that male brains are genetically programmed to be different from women's.

These scientists analyzed thirty samples of human brain tissue taken from different sections of the brain and from different individuals. They were not told the sex of the individual from whom each specimen was taken, and simply by genetic analysis of the brain tissue they were able to correctly identify the sex of every sample.

Neuroscientist Larry Cahill, in an article for Scientific American, wrote that the structural, chemical, and functional differences between the brains of males and females raise the possibility of developing “sex-specific treatments” for conditions such as depression and schizophrenia.

Toys 

The differences between male and female brains affect many aspects of behavior and perception, including memory, emotion, vision, hearing, how we handle stress—and even the toys we like to play with.

Researchers (and parents) have noted boys are more likely to play with balls and cars, whereas girls tend to prefer dolls and Easy-Bake ovens.

Those who claim that "gender" is a social construct find this abhorrent. Earlier this year, Boots, the largest pharmacy chain in the U.K., felt compelled to take down the signs for "boys" and "girls" toys after shoppers took to Facebook and Twitter to accuse the retailer of "sexist behavior." Meanwhile, in Sweden they’ve begun pushing “gender-blind” toy catalogs picturing girls shooting toy guns and boys blow-drying hair.

Although it flies in the face of political correctness, science strongly suggests that the reason boys and girls prefer to play with different toys has less to do with cultural conditioning than with brain biology.

In 2002, Melissa Hines of City University London and Gerianne M. Alexander of Texas A&M University decided to conduct experiments on vervet monkeys, one of our closest biological cousins. They found that the monkeys showed “sex differences in toy preferences similar to those documented previously in children." The boy monkeys typically preferred playing with cars and balls, while the female monkeys preferred playing with dolls and pots. (And they didn’t have parents or toy catalogs telling them which they should prefer.)

They concluded that such “sexually dimorphic preferences” for certain features in objects are deeply embedded products of evolution, preferences related to the very nature of being male or female—preferences that human children also clearly exhibit.

All that differentiates men and women is what’s "between their legs"? Far from it.


Matt Fradd is Australian by birth and Catholic by choice. After experiencing a profound conversion at World Youth Day in Rome in 2000, Matt committed himself to inviting others to know Jesus Christ and the Church He founded. As a missionary in Canada and Ireland, Matt proclaimed the Gospel to over ten...

Comments by Catholic.com Members

#1  Jen M - Dayton, Ohio

I don't deny that there are real gender differences that differentiate women from men. But as a person with a science background, I need to say something that I hope will help you write articles in the future.

If you are going to cite a scientific paper, please make sure that you are conveying the information in the paper truthfully. From what you've written, it sounds like the point of the study was to see if they could tell the difference between male and female brains just by doing a genetic test as if it was a game - "Here are brain samples. Can you guess if it's male or female?" But that wasn't the point of the study at all.

If the point of the study was to guess whether or not the sample was male or female, a simple karyotype would suffice. The government wouldn't fund a study if that was the point.

The study was looking at gene expression in the brain and whether or not there were differences between males and females - they *did* know the sex of the samples from the beginning. Perhaps I missed where they said they didn't, but it would've been a lot of time wasted if they didn't keep track of the gender from which the samples came.

The "big" point of the study was to find gene expression differences that could explain the differences in prevalence of various neuropsych disorders. In fact, the study DID find some differences.

So in the end, the study can still be used for the point you want to make - male and female brains are different. But it didn't say what you said.

August 27, 2013 at 10:29 pm PST
#2  Jen M - Dayton, Ohio

That was probably written harsher than I meant it to be. It just irks me when people misinterpret science articles and use it as evidence to support their claims.

Regardless, the main point of your article is an interesting one, and I can guess what news story inspired you to write this.

Food for thought:
If "what's between the legs" defines sex, then what about people who are completely androgen insensitive (CAI) - they look physically like a female but are genetically XY, which we define as male (and actually, because of the genetics, they're missing female reproductive organs).

That really shakes up how we define gender/sex - it's not simply genetics nor simply a social construct. It's not a simple black and white answer, and I think it's unfair to say that social constructs don't play any role in defining "femaleness" or "maleness."

The topic deserves more thought than simply ignoring the gray areas. Even if we biologically define people with CAI as male (since they're XY), how do we treat them? As a male or a female?

August 27, 2013 at 11:02 pm PST
#3  Shae S - Granbury, Texas

I'm curious as to what the Catholic perspective is on the individuals who do not fall into the category of "most". For example, females who prefer to play with cars and balls or males who prefer dolls and ovens?
Are they viewed as disordered? Is this considered acceptable?
Thanks

August 28, 2013 at 6:53 am PST
#4  Erica Perry - wetumpka, Alabama

In response to Jen M:

The literal wording:

"published findings showing that male brains are genetically programmed to be different from women's"

Which is exactly what the study was about.

It does not hint a "guessing game" as you put it. Also, if you wish to say that the above excerpt, in itself, is incorrect, it merely is upheld by what you said:

"the study was to find gene expression differences that could explain the differences in prevalence of various neuropsych disorders. In fact, the study DID find some differences"

August 28, 2013 at 9:01 am PST
#5  Jen M - Dayton, Ohio

The part that was incorrect was this one:
"They were not told the sex of the individual from whom each specimen was taken, and simply by genetic analysis of the brain tissue they were able to correctly identify the sex of every sample."

August 28, 2013 at 9:22 am PST
#6  Don Allen - perrysburg, Ohio

Perhaps this is where the author inferred they could predict if it were a male or female brain.

" The gender classification of each sample was accurately predicted by subtracting the microarray expression of DBY from XIST, which reliably differentiated male and female samples in all brain regions. "

August 29, 2013 at 5:11 am PST

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