3150 words

Introduction

Almost seven years ago I argued that there is such a thing as a “male” and “female” brain. Now, I’m not so sure on that belief. Because a claim like that reduces to the claim that there are two different KINDS of brain—make and female. This, though, is basically a mereological fallacy. Brains aren’t gendered/sexed, people are. Brains don’t have genders, people have genders. This doesn’t mean that there are no sex differences in the brain, that claim would be ridiculous. But the actual claim—a claim that I think is perfectly defensible—is that there ARE NOT two different kinds of brain. This is the conclusion that I will argue for in this article.

The brain mosaic

Questions like “Is the brain gendered?” are the wrong kinds of questions to ask. Not only is it implying that there is more than one kind of brain, it is also implying that the brain is itself gendered. The claim that the brain is gendered is patently false; brains don’t have genders, people have genders, and people aren’t—nor do they reduce to—their brains. Therefore brains aren’t gendered.

When does a feature of a brain count as that which is typical of a male brain and vice versa for women? How many of these differences would there need to be in one brain to designate that brain as male or female? Of course there are average differences which I don’t think anyone would deny, but these average differences between brains wouldn’t license the claim that there are two different kinds of brain just like the fact that there are average differences in hearts between men and women don’t license the claim that there are two different kinds of heart. The only clear-cut average difference between the brains of men and women are that of size—women’s brains are about 11 percent smaller than men’s when body size is accounted for (Eliot et al, 2021). But mere size differences, also, do not license the claim that there are two different kinds of brain. For there to be male and female brains—two types of brain—there needs to be a property or set of properties which are exclusive to the two brains, but there are no such properties. Again, no one denies average sex differences, what is denied is that there are two different kinds of brain.

In recent years, talk in the neurosciences have shifted away from such a binary claim to that of mosaicism (Joel, 2011, 2012, 2021; Joel et al, 2015). Fine, Joel, and Rippon even have an explainer about sex, gender, brains and behavior. Joel et al (2015) analyzed four datasets of 1400 individuals examining the size and characters of brain regions that show the largest sex differences. They found substantial overlap between features, and that, on each end of the distribution, there were more males and more females, respectively. However, they had a novel finding: Many of the brains that were analyzed had many components of each “kind” of brain—they contains a mosaic of each of the ends of the distribution (male and female). Thus, the claim that brains are a mosaic or intersexed are true. So sex doesn’t determine brain type and, even though there are average differences between men and women, these average differences don’t add up to the claim that there are two different kinds of brain. Sex is dimorphic, but brains aren’t—brains are monomorphic.

Monomorphic not dimorphic

Sexual dimorphism is where the genders of a specific species have differences that aren’t solely (that is, not related to) due to their sexual characteristics. Monomorphic species, though, are similar in everything but their sexual characteristics. There is only one form with all individuals in that species having the same physical characters with little to no variation in them. So the claim that brains are dimorphic means that there are two kinds of brain—meaning, male and female. These terms (monomorphic and dimorphic) refer to variation in traits, with the term monomorphic referring to little or no variation while the term dimorphic refers to a situation in which there is noticeable variation. Certain bird species have different physical characteristics such as sex-specific markings, size differences and color differences which would mean they are dimorphic. On the other hand, other kinds of bird species may have the same kinds of physical characteristics meaning they are dimorphic.

If there is only one form of trait in a population, then the population is monomorphic. If there are two distinct forms of a trait in a population, then that population is dimorphic. Thus if there is little to no variation in the expression of a trait within a population then that population is monomorphic; if there is noticeable variation in the expression of a trait in a population then that population is dimorphic.

Eliot et al (2021) showed that brains aren’t dimorphic, they are monomorphic. The only reliable difference between the two are that of brain size, with women having an 11% smaller brain than men, which is smaller than that of the heart, lungs, and kidneys. Therefore, once brain size is accounted for, there are little no variation between brains (Eliot et al state the few reliable differences between brains are byproducts of brain size, so brain differences between sex/genders “explains” 1 percent of the total variance which means that brain differences which could be attributed to sex and gender are minuscule compared to individual variation.)

But for all the surplus of brain-level data on male-female difference, surprisingly few clear findings have emerged, and even less to justify labeling the human brain as “sexually-dimorphic.” Nor does anything in this massive data collection actually explain male/female differences in psychology or mental health (De Vries and Södersten, 2009; Hirnstein et al., 2019) in spite of decades of such promise. To the contrary, the data show that male and female brains are overwhelmingly similar, or monomorphic, and suggest that finding such neural correlates will more fruitfully be achieved through study at the individual, as opposed to s/g group level.

…

Rather, a picture is emerging not of two brain types nor even a continuous gradient from masculine to feminine, but of a multidimensional “mosaic” of countless brain attributes that differ in unique patterns across all individuals (Joel et al., 2015). Although such differences may, in a particular sample, sum up to discriminate male from female brains, the precise discriminators do not translate across populations (Table 7; see also Joel et al., 2018; Sanchis-Segura et al., 2020) so are not diagnostic of two species-wide types. In this sense, the brains of male and females are not dimorphic (like the gonads) but monomorphic, like the kidneys, heart and lungs, which can be transplanted between women and men with great success. (Eliot et al, 2021)

Mccarthy and Arnold (2011) explain why the belief that there are sex-specific circuits, which is due to the investigation of a small number of dimorphisms in the brain:

The repeated investigation of a relatively small number of sexual dimorphisms may have contributed to the false impression that a few discrete male or female circuits sit in an otherwise sexually monomorphic brain. The notion that for specific behaviors there is a discrete male neural circuit versus a discrete female neural circuit remains widely held despite a lack of empirical evidence of the existence of either.

The argument against the “two kinds of brain” argument

In this section, I will synthesize the preceding sections into an argument which argues that there aren’t two kinds of brain, male and female.

P1: If there are two kinds of brain (male and female) then there should be clear and distinct differences in brain structure and function between men and women.
P2: Studies have shown that there is a wide range of variation in brain structure and function among individuals of the same sex and also between men and women.
C1: Therefore, the available evidence doesn’t support the claim that there are clear and distinct differences in brain structure and function between men and women.
P3: The claim that there are two kinds of brain (male and female) is based on the assumption that there are clear and distinct differences in brain structure and function between men and women.
C2: Therefore, the claim that there are two kinds of brain (make and female) is not supported by available evidence.

Premise 1: This premise is based on the assumption that male and female brains are fundamentally distinct from each other, to such an extent that they can be categorized into two separate categories. There is, though, much overlap between the structure and function between brains belonging to men and brains belonging to women. For example, the Joel et al (2015) study cited above concluded that there is no such thing as a “male” and “female” brain, but there is a continuum of brain characteristics which are influenced by G and E factors. Rippon et al (2014) don’t argue that there are no differences in brain structure and function between sexes, but they do argue that such differences don’t license the claim that there are two forms—kinds—of brain. It is, again, important to note that none of these researchers argue that there are no sex differences; the claim is that these sex differences don’t add up to make “male” or “female” brains, they don’t belong to two different categories. Joel and Fausto-Sterling (2016) write:

We argue that the existence of differences between the brains of males and females does not unravel the relations between sex and the brain nor is it sufficient to characterize a population of brains. … Studies of humans further suggest that human brains are better described as belonging to a single heterogeneous population rather than two distinct populations.

Premise 2: The references on the brain mosaic back up P2. The differences that do exist are small (as noted by Eliot et al, 2021) and these differences do not support that claim that human brains are dimorphic. There is much overlap between brains of men and women and even significant variation in brain function and structure between individuals of the same sex.

Conclusion 1: Based on the two previous premises, the claim that human brains are dimorphic are clearly false. Differences are not clear-cut (and what differences do exist are small) and there is no one property or set of properties between brains that would designate one “male” and another “female.”

Premise 3: P3 is based on the history of this kind of research, in which it was assumed that there are two different kinds of brain—male and female. Jordan-Young and Rumiati (2012) argue that much of the research on sex differences in the brain is based on the binary assumption—since sex is binary, then the brains inside of the heads of the individuals must be sexed too. They assume that such differences exist in the brains exist and then go looking for them. Of course, more often than not, if you’re looking for something you’re going to find it. At the end of the day, the fact that sex and gender (s/g; Eliot et al, 2021) are so tightly interwoven (but still distinct) that even if there are biological differences, untangling them will be next to impossible, just like when it comes to heritability and the nature-nurture debate.

Conclusion 2: This conclusion logically follows from P3, since the claim that there are male and female brains is based on an outdated and oversimplified understanding between biology (brain) and sex. Any differences that do exist are small, influenced by numerous factors, and fall along a continuum, not a dimorphic binary.

So it thusly follows that there are not two different kinds of brain; the dimorphic assumption is false and brains, like other internal organs, are monomorphic.

Gender isn’t natural

Here, I have two arguments. One that establishes that gender and sex aren’t the same, and another that establishes that gender is not natural (it is social).

P1: If gender and sex are the same, then the characters and roles associated with being male and female are biologically determined.
P2: The characters and roles associated with being male and female are not purely biologically determined.
C: Thus, gender and sex are not the same.

P1 is based on the assumption that if g and s are the same, then all characters associated with male and female are biologically determined. Gender is a social construct which changes with the times and is different across cultures and time periods. (Like, for example,) So this indicates that such differences are not solely biologically determined. P2 states that gender roles are context- and time-sensitive. So roles and expectations of men and women are not solely biologically determined. The conclusion then logically follows: If the differences between men and women aren’t purely biologically determined, then gender doesn’t reduce to biology. So sex and gender are different because the characters and roles of men and women aren’t purely biologically determined, which means that gender isn’t reducible to biology.

Now here is my argument that gender is not natural, meaning it is social:

P1: All things that are “natural” are socially unmediated and inevitable (all A are B).
P2: Gender is socially-mediated and not inevitable (C is not B).
C: Therefore, gender is not natural (C is not A).

I think P1 is the only premise that one would reject. But to best defend P1, I only need to appeal to the definition of “natural.” “Natural” refers to anything that exists in the world independent of human society, culture, or intervention. Natural phenomena aren’t socially-mediated meaning that they aren’t shaped by human norms, values or practices and are inevitable due to certain physical laws. By “socially unmediated” I mean a phenomenon which isn’t dependent on human values, norms, or practices which occur independent of human intervention which are not subject to variation or change based on social context or historical period. By “inevitable” I mean phenomena which are subject to natural laws which are universal and unchanging. I can also defend P1 by arguing the distinction between facts and values. Natural phenomena are facts that exist beyond human values. Anything that is subject to human values or norms would be socially mediated, which would include gender.

Now that I have successfully defended P1, to defend P2 one easy example is that of color. It has been argued that men and women prefer different colors due to our hunter-gatherer ancestry (Hulbert and Ling, 2007). Pink used to be seen as a color for boys while blue used to be seen as a color for girls. (See here and here.) The conclusion then follows, since the premises are true and the argument is valid.

Men and women and IQ

Lastly I will discuss the preceding arguments in the context of IQ. For example, Lynn (1994) argues that there is a 4 point difference between men and women in IQ, and relates it to selection pressures. Kanazawa (2009) argues that men have higher IQ than women since men are taller than women, and when height is controlled, women have higher IQ. Irving and Lynn (2006) and Lynn and Kanazawa (2011) also note a small difference between the sexes. But Halpern and Wai (2019) rightly note the historical reasons why there is such a small—almost nonexistent—difference in IQ between men and women:

Massive amounts of data show that although there are some on average differences in specific cognitive abilities, there is considerable overlap in the male and female distributions. There are no sex differences in general intelligence – standardized IQ tests were written to show no differences, and separate assessments that were not written with this criterion show no differences in general intelligence.

When creating his Stanford-Binet test, Terman thought that men and women should be equal in IQ, and so he adjusted his test to reflect this (a priori) assumption. Ackerman (2018) describes this well:

There is an important historical reason why there are negligible gender differences in omnibus IQ assessments. … Terman … decided that there was adequate justification for equality of IQ scores across the sexes, and so he constructed his IQ test to be specifically balanced.

We don’t need to use differences in height, or stories about evolutionary selection pressures, or differences in brain size to explain the small difference between and women on IQ tests. We only need to look at how the tests are constructed, as the considerations from Terman and also Rosser (1989) show. Thus, we don’t need to look to biology and brains to explain the small difference. It is due to how the tests are constructed.

Conclusion

Taken together, the three sections here point to one conclusion: The nonexistence of male and female brains means that gender doesn’t reduce to biology (the brain), nor do brain differences cause IQ differences between men and women. While hereditarians do argue that the brain size differences between men and women “explain” the slight 4 point or so difference in IQ between men and women, and while women do have about an 11 percent smaller brain than men on average, this does not (1) license the claim that brain size is causal for the small IQ differences and (2) justify the claim that there are two distinct kinds of brain (male and female). So claims from people like Murray (2020) that there are two kinds of distinct brain fail. When does a feature count as “typical” of the so-called male or female brain and how many of these features would one of these brains need to have to be designated as male or female? Brains aren’t gendered or sexed, people are, and people aren’t their brains.

P1: If male and female brains don’t exist, then any observed differences in cognitive ability between men and women are likely to be explained by cultural and social factors along with how the tests are constructed.
P2: Male and female brains do not exist.
C: Thus, any observed differences in cognitive ability between men and women are likely to be explained by cultural and social factors along with how the tests are constructed.

Brains are not sexed or gendered, humans (and their selves) are sexed or gendered. While gender identity does exist, it’s irreducible to biology and it is a form of personal identity. As I stated at the outset, the claim that there are male or female brains or that brains are sexed is a mereological fallacy since those are properties of the whole (human) rather than their parts (the brain). These arguments also have implications for claims that transgendered people have brains of “the other sex.” For if two types of brains do not exist, then those claims are false. “Brain sex”, therefore, is a nonsense, incoherent term. Human brains are monomorphic, not dimorphic.