A few months ago a Scientific American editorial claimed that “most of us are biological hybrids on a male — female continuum”. The editorial managed to upset the scientific community. I first heard of it when Steven Pinker, a cognitive scientist at Harvard, tweeted a link to a sound rebuttal of the editorial by University of Chicago biologist Jerry Coyne. This bit of controversy piqued my interest. Fast forward to this past week when I heard “trans studies” professor Nicholas Matte flat out claim that biological sex doesn’t exist. It appears the idea that biological sex either doesn’t exist or is a social construct is becoming more popular. So does it exist? Is it simply a “social construct”?

Chromosomes play an important role in human sexuality.

Biological sex vs gender

First, a distinction must be made between biological sex and gender. According to the APA Dictionary of Psychology sex is:

“The traits that distinguish between males and females. Sex refers especially to physical and biological traits, whereas GENDER refers especially to social or cultural traits, although the distinction between the two terms is not regularly observed.”

Or according to “Guidelines for psychological practice with lesbian, gay, and bisexual clients”,

“Sex refers to a person’s biological status and is typically categorized as male, female, or intersex (i.e., atypical combinations of features that usually distinguish male from female). There are a number of indicators of biological sex, including sex chromosomes, gonads, internal reproductive organs, and external genitalia.”

And one more for good measure. Planned Parenthood (American Federal Government) says:

“Sex is a label — male or female — that you’re assigned by a doctor at birth based on the genitals you’re born with and the chromosomes you have. It goes on your birth certificate.”

So just to emphasize, I’m discussing biological sex and not gender.

What is Biological Sex?

The fact is that the overwhelming majority of human beings are born with either an XY or XX chromosomal constitution. About half the human population is born with an XY chromosomal constitution and the other half is born with XX. This is what’s referred to as a bimodal distribution. Of course, intersex people are an exception. Intersex births account for roughly 2% of the human population. So roughly 98% of all humans are born with one of these two chromosomal constitutions.

A classic bimodal distribution.

But to simplify biological sex to the presence or absence of a Y chromosome is still incorrect. This would imply that there is a strict “binary” wherein biological males exhibit a set of traits and biological females exhibit another unique set of traits with zero overlap. There are however, varying degrees of differences on average between males and females. To explain this I will quote psychologist Dr. David P Schmitt at length:

“One way to clarify discussions about differences in group averages is to put a specific number to them. Psychologists often use a precise number to express the size of sex differences, referred to as an “effect size,” with the most common usage being the d statistic. A positive d value typically indicates that men are higher on a particular attribute; a negative value indicates that women are higher. The size of the d value establishes exactly how big the average sex difference is. A d value near zero means that the sex difference is trivial. Once a d value reaches +/- 0.20, psychologists take notice. A d value of -0.20, for instance, indicates that 58 percent of women are higher than the average man on a psychological trait. These are considered “small” effect sizes. Sex differences in interpersonal trust, conformity, and general verbal ability reside in this range. A d value of +0.50 is considered “moderate” and indicates that 69 percent of men are higher than the average woman on a particular attribute. Sex differences in spatial rotation skills, certain mathematics abilities (3-dimensional geometry and calculus), and task-oriented leadership (focusing on accomplishing a group goal rather than maintaining harmony within the group) reside within this size range. A d value of -0.80 is considered “large” and indicates that 79 percent of women are higher than the average man. Sex differences in tender-mindedness, being interested more in people than in things, and lack of interest in casual sex reside in this size range. Larger d values are less common in psychology, but a value of +1.00 indicates that 84 percent of men are higher than the average woman. Sex differences of this magnitude include differences in height, in expressing interest in engineering as an occupation, and in absence of sexual disgust (such as not feeling grossed out when hearing the neighbors having sex). A d value of +2.00 indicates that 98 percent of men are higher than the average woman in a trait, about as close as researchers can get to finding a truly dimorphic difference. Sex differences in throwing ability, grip strength, and voice pitch are in this range. No matter how big or small a sex difference, there is almost always significant overlap across distributions of men and women. Some women are able to throw farther than some men. Psychological sex differences are about group distributions, not dichotomous binaries of all men versus all women.”

Reviewing the Data

In fact the sexual differences between men and women are increasingly supported across disciplines. As Schmitt notes:

“Converging lines of empirical evidence — from developmental neuroscience, medical genetics, evolutionary biology, cross-cultural psychology, and new studies of transsexuality — along with our evolutionary heritage, all point to the same conclusion: There are psychological differences between men and women.”

And indeed the evidence is rather overwhelming. A quick review of the literature shows that in the hard sciences (e.g. biology, neuroscience) as well as cognitive science the question isn’t whether biological sex exists, but rather the how much biological sex influences our behavior. For instance, it has been demonstrated that prenatal androgen exposure has serious impact on behavior including toy preferences, occupational choice, and even gender development (also see here). Additional studies have shown males are biologically predisposed to higher rates of autism and women are more likely to suffer from depression, in part due to biological causes.

And the psychology literature paints a similar picture: biological females generally score higher in neuroticism (No, not that neuroticism. I mean technically.) and agreeableness (again, a technical term). Additional studies further support these findings.

Neuroscientific literature not only supports the existence of biological sex, but entirely accepts its existence and develops studies to understand its impact. Male and female brains are shown to differ in connectivity, percentage of gray matter, memory, and brain aging. In fact, neuroscience has more clearly delineated the impact of biological sex than most other fields. An article in Nature Reviews Neuroscience even went so far as to say that:

“Research into sex influences is mandatory to fully understand a host of brain disorders with sex differences in their incidence and/or nature. The striking quantity and diversity of sex-related influences on brain function indicate that the still widespread assumption that sex influences are negligible cannot be justified, and probably retards progress in our field.”

The Origins of Biological Sex Denial

The question that arises is why — despite such compelling evidence of the impact and importance of biological sex — do some social scientists continue to reject its importance (or even existence!)? That is to say, why is the existence of biological sex a non-issue in the hard sciences but conspicuously under scrutiny elsewhere in academia?At least in part, the rejection of biological sex seems to stem from disciplines which either reject objective science outright or suffer from systemic replication problems. The latter group is made up of fields like social psychology where “findings were less than half as likely to replicate as findings in cognitive psychology”. The former group primarily consists of fields like women’s studies, gender studies, ethnic studies, and trans studies. In every case it’s likely that a belief in the so called “blank slate” theory is motivating the researchers within the social sciences. This theory denies that evolution affected the development of the human mind. Which is a rather incredible belief when you really think about it. Not surprisingly, Harvard cognitive scientist Steven Pinker wrote a popular book debunking the blank slate in 2002. In it he details how biology and the hard sciences have rejected the theory for decades, but somehow the idea has managed to stay alive in the social sciences. Funny how the more things change, the more they stay the same, eh?

The Blank Slate by Steven Pinker

So clearly biological sex exists. Some activists (and social scientists in the above disciplines) reject the distinction of biological sex because it “alienates” or “marginalizes” the intersex community. However, the terminology of “male” and “female” is used to represent the bimodal distribution of biological sex. It’s a useful term. To reject it simply because it “marginalizes” is ludicrous. Here’s why: Humans are also biologically categorized as binocular animals. We typically have two eyes. Doesn’t that “marginalize” humans born with Cyclopia, a birth defect which produces one eye? Humans are also considered bipedal. That term necessarily “marginalizes” humans born with one leg. So on and so forth. When approached logically the claim that “biological sex” marginalizes becomes a statement of obvious fact. Language categorizes and thus marginalizes, by definition. The fight against biological sex isn’t just a revolt against scientific consensus. It’s a revolt against language itself.

So is biological sex a social construct? Well sure, in the same way that the words “dog” or “cat” are social constructs. Language itself is a social construct. This statement of obvious fact doesn’t tell us very much, however. What people typically mean when they claim that “biological sex is a social construct” is that biological sex is entirely divorced from biology. This claim is false.

Final Thoughts

I started writing this out of pure scientific curiosity. But after reviewing the literature across disciplines it became incredibly clear that certain fields of study must ask themselves why it is that they’re in disagreement with the hard sciences. How is it that a concept that’s been accepted by biology and neuroscience for decades could be abruptly rejected by outsiders? And what are the consequences of fields of study which often openly deny the scientific method? Could it be that rejecting the scientific method becomes a useful tool when science doesn’t agree with your ideology?

In the end I can’t stop someone from insisting that biological sex is a social construct or denying its existence altogether. After all, all one needs to do is look up a women’s studies journal and find some “autobiographical” essay demonstrating that objective facts are a tool of the patriarchy and boom, game over. The real question become what is knowledge and which sources of knowledge do you trust? Ultimately that decision is up to the individual. And if an individual chooses to deny objective scientific truth, that’s fine. I just wish they would stop hiding behind science while doing so.