Idea: the scientific method has generated a large body of useful knowledge. This method discovers ‘facts’ if facts are things that are highly likely to be true; it doesn't create dogma. The biology of sex is just one area of knowledge generated by this method. Some people are trying to redefine sex based on their own set of beliefs. However, these beliefs are dogmatic and can’t compete with the effectiveness of the scientific method and the body of useful knowledge it’s generated. This knowledge shows that sex in humans is binary and too complex to change.
I need a post about the biology of sex to complement the one I wrote on Gender. What I would like to do with this post is give you a genuine account of how science understands sex, and then discuss how the scientific method has generated this knowledge.
I’ll describe some concepts first:
-(Biological) Function – this is the purpose behind some biology and the glue that coordinates its parts. In the case of sex, it’s reproduction.
-Genotype – the set of instructions (eg, genes) that define the limits and potential for an organism.
-Phenotype – the realisation of an organism’s genotype within some environment. This will also be influenced by random variation during development (ie, because the genotype can’t exactly plan the outcome).
-(Biological) Variation – take height, someone’s genotype can determine the range of possibility but their exact height (the phenotype) will be influenced by their environment (eg, nutrition) and randomness as their body develops. In contrast to this normal variation, there’s abnormal variation due to (typically) errors in the genotype.
-(Evolutionary) Selection and fitness – these are concepts from evolutionary theory; they basically mean that any variation in the genotype will be selected by evolution to persist across generations if it improves how well an organism fits into its environment.
-Distributions and averages – the toy graph in my post Gender illustrates these concepts. It’s very difficult to discuss the topic of sex and gender unless people understand these ideas. The average of some distribution will be an abstraction removed from the real things that generated that average but it may still be useful and give insight.
Now I've outlined some concepts I’ll give an overview of the biology of sex while also highlighting some scenarios that appear to question this knowledge.
Apart from a relatively small number of differences, males and females share the same basic set of instructions for how to build a human. There are about 30,000 genes in the human genome, plus lots of genetic information surrounding these genes that regulate them. What differs between males and females is the time and place this genetic information is engaged. This leads to two outcomes: specific differences between the sexes, such as genitals; or, the relative proportions between shared features will differ based on sex, such as with facial features. Both of these situations require an incredible degree of coordination so that the end result produces a human that can perform all the functions that are required to survive and reproduce. All parts of the genome will be directly and indirectly affected by this moth vs butterfly transformation, and this biological process is so complex it’s taken millions of years to evolve.
In humans, the genetic instructions selected by evolution that allow us to reproduce only produce two functional outcomes, males and females. As I’ll detail below, one of the simplest ways to see this is that when the signals that engage either the male or female route are weakened it generates a phenotype that has no functional relationship to the purpose of sex (ie, reproduction), and in fact may prevent it. There will be other sources of variation as well, as is normal for the genotype to phenotype relationship. The genotype can’t exactly determine the phenotype, so someone’s environment plus randomness during development will contribute to the eventual outcome. Again, as before, this variation has no functional relationship to the purpose of sex.
Before I examine various scenarios that cause confusion within this debate, I’ll quickly summarise some key ideas I think act as criteria for deciding whether something is part of the biology of sex. Firstly, there must be a functional relationship that would have been selected for by evolution. Secondly, variation per se is not part of the biology if it has no functional relationship to it. Thirdly, the biology of sex has to be consistent with the rest of biology and science; arbitrary claims about what should be included within the scope of the biology of sex should be treated by the same standard as any other area of science.
Some people misunderstand the relationship normal biological variation has to sex classification. Take faces. Noses, mouths, and eyes will have a distribution in size and shape that happens for no other reason than evolution has decided a certain amount of variation is tolerable. Males and females will on average have facial features that are similar in size and shape but there will inevitably be some overlap. A male with a ‘feminine’ nose isn’t less male. It’s just a random event unconnected to their biological sex. Also, when you have millions of people it’s inevitable that some individuals will by chance alone have a nose, mouth, and eyes etc that appear to be more like the opposite sex, but again this is just a random event. This kind of variation has no functional relationship to biological sex and therefore plays no role in sex classification whether that’s with the sex binary or as evidence for a spectrum of sex.
Another source of variation are mutations in the genotype. Mutations are a routine part of our biology. In fact, our biology is effectively the result of millions of years of mutations selected by evolution because they improved our ability to fit into our environments. What’s important here is that it’s selection not mutations that’s important. In other words, the mutations have to have some functional relevance to the biology. There are multiple ‘disorders of sexual development’ (DSD) that consist of these non-functional mutations. In some cases, the signals that orientate our genotype towards the male or female route are weakened, but rather than create a functional intermediate phenotype they create a condition that justifies the label ‘disorder’. There’s no reason to treat a DSD any differently than other instances of biology impacted by non-functional mutations. Someone with a DSD is, or would have been, either a male or a female but instead they have a sex specific disorder. DSDs are not evidence of a spectrum of sex because they have no functional relationship to the biology of sex.
So, people’s bodies are either male or female, but what about their brains? Our brains are made up of areas specialised for various aspects of our mental activity. It’s possible these areas, on average, differ based on biological sex, and there’s evidence to support this. Similar to the faces example above, it’s therefore possible that males, for example, may due to chance have brain areas, or even many areas, that are more like those found in females. Alternatively, like people with a DSD, there may be situations where males have female-like brains without that being something that was selected for during evolution. Do these two scenarios mean that a male with a female-like brain is less of a biological male? No. These differences are just the result of non-functional variation.
An interesting alternative is that evolution has designed the human brain to differentiate along two paths that have subsequently been labelled as masculine and feminine, and society assigns these traits based on biological sex even though they’re spread across both sexes. However, because evolution has evolved these innate behaviours to be present in both sexes they’re not therefore functionally related to sex. It’s just society that’s created this association. I’ll discuss in another post how these ideas may help to explain why some trans people feel they’re the opposite sex.
In summary, whether it’s the body or the brain the biology of sex has only one purpose: to facilitate reproduction via males and females. Non-functional variation that’s superficially related to sex is irrelevant to this biology. You can only be a male or a female, and these two states are so complex and differentiated that it’s impossible to transition between them.
How was this knowledge generated? I’ll leave the details for other posts, but the scientific method is a general-purpose means to observe the world with increasing resolution. Properly understood, this method and its output is still dependent on belief, but its closeness to truth can be readily measured by its explanatory power, usefulness, and consistency. It has openness and doubt baked into it; if it didn’t, it wouldn’t have progressed.
In opposition to the scientific method and its body of knowledge are the claims of gender identity theory. For example, that sex is socially constructed, or that it isn’t binary. The claims of this theory are a good way to illustrate the focus of Structured Openness. I can take seriously that part of gender identity theory where I'm required to be open. It may well be the case that sex isn’t binary, for example. However, this theory has no useful structure, and can’t produce any. It just consists of unproductive beliefs and unevidenced claims.
Gender identity theory can’t compete with the scientific method and the body of knowledge it’s generated. It has no means to generate useful concepts such as genotype, phenotype, variation, and natural selection. Belief in the scientific method can give structure to openness in a way that beliefs like gender identity theory can’t. In fact, such beliefs are dogmatic and in opposition to being open.
You’re smarter when you believe in the scientific method and its output. Don’t believe me? Trying living without it, which is what beliefs like gender identity theory require. Why? Because the biology of sex is just one part of a system of knowledge generated by the same method. Dismiss the biology of sex and you dismiss science.
This post has already been longer than I would normally like a post to be, but I'll say one last thing. Gender identity advocates frequently say ‘transwomen are women’ and ‘transmen are men’. If male and female refer to biological sex, then the science on this issue is clear: transwomen are male, and transmen are female. I’ll discuss whether they’re men and women in another post.
Subscribed! 🙂 Looking forward to seeing your use of "the scientific method" to bring some scientific principles to the "debates" over the definitions for sex and gender – something that those "debates" are in desperate need of.
And likewise like your "statement of principle" – nailed to the masthead – that "there is an objective, structured world that can be understood via evidence and reason". Reminds me of a passage from a book – The Mind of God – by Australian professor of mathematical physics Paul Davies:
"The claim that the world is rational is connected with the fact that it is ordered. Events do not happen willy-nilly: they are related in some way." [pg28]
In any case, relative to your "Sex" post, I quite agree with you starting out by describing some concepts. I've often quoted Voltaire's quip, "if you wish to converse with me then define your terms", a crucial step that far too many miss. But in particular, I like that you've drawn a line in the sand, that you’ve emphasized “function”, that you've stipulated that sex is all about actual reproduction, that it's "the glue that coordinates its parts". Entirely consistent with the standard definition for sex:
"Sex: 2) Either of the two main categories (male and female) into which humans and most other living things are divided on the basis of their reproductive functions."
https://www.lexico.com/en/definition/sex
“functions”, indeed; that without which not, the “sine qua non” of the sex categories.
However, what seems conspicuous by its absence is where you define precisely what is meant by "male" and "female". It would seem to be rather difficult to challenge those who "are trying to redefine sex based on their own set of beliefs" if one doesn't have in hand a set of definitions based on the "scientific method" or on cogent epistemological principles.
But rather depressing that there seems to be such a large field of people – including various “scientism-ists”, the delusional, an odd-lot of politically-motivated hacks and dogmatists, and a bunch of otherwise credible “biologists” and “philosophers” who should know better – who are engaged in that “redefinition”. ICYMI, there’s quite a good essay – “Ideological Bias in the Psychology of Sex and Gender by Marco Del Giudice of the University of New Mexico – that underlines the essential element of “function”, and that delineates the standard biological definitions versus the “patchwork definitions of the social sciences”:
"On a deeper level, the ‘patchwork’ definition of sex used in the social sciences is purely descriptive and lacks a functional rationale. This contrasts sharply with how the sexes are defined in biology. From a biological standpoint, what distinguishes the males and females of a species is the size of their gametes: males produce small gametes (e.g., sperm), females produce large gametes (e.g., eggs; Kodric-Brown & Brown, 1987)"
https://www.researchgate.net/publication/346447193_Ideological_Bias_in_the_Psychology_of_Sex_and_Gender
You might also be interested in an essay at Aeon by Paul Griffiths – university of Sydney professor, philosophy of biology, co-author of “Genetics and Philosophy” – and this passage in particular:
"Nothing in the biological definition of sex requires that every organism be a member of one sex or the other. That might seem surprising, but it follows naturally from DEFINING each sex by the ability to do one thing: make eggs or make sperm. Some organisms can do both, while some can't do either [ergo, sexless]."
https://aeon.co/essays/the-existence-of-biological-sex-is-no-constraint-on-human-diversity
Basically, pretty much the same definition that is front-and-center in most credible dictionaries, encyclopedias, and various journals, and is endorsed by more than a few credible biologists including Geoff Parker (FRS, emeritus professor of biology, University of Liverpool) and Jussi Lehtonen:
"Biologically, males are DEFINED as the sex that produces [present tense indefinite] the smaller gametes (e.g. sperm), implying that the male and female sexes only exist in species with gamete dimorphism (anisogamy)."
https://academic.oup.com/molehr/article/20/12/1161/1062990
https://www.mdpi.com/2073-4409/10/3/573
https://www.sciencedirect.com/science/article/abs/pii/0022519372900070
https://www.lexico.com/en/definition/female
Curious though that so many of those attempting to redefine sex as other than the above biological definitions try to fall-back on a structure-only definition, i.e., no actual function required. For instance, philosopher Kathleen Stock argues that:
“A plausible and much more minimal alternative says that each sex is defined by the presence of a developmental pathway to produce certain gamete types …”
https://lcp.law.duke.edu/article/the-importance-of-referring-to-human-sex-in-language-stock-vol85-iss1/
Along the same line, evolutionary biologist Colin Wright argues that:
“Yet it would be incorrect to say that these individuals [the prepubescent, the infertile] do not have a discernible sex, as an individual’s biological sex corresponds to one of two distinct types of evolved reproductive anatomy (i.e. ovaries or testes) that develop for the production of sperm or ova, regardless of their past, present, or future functionality.”
https://www.realityslaststand.com/p/sex-is-not-a-spectrum?s=r
However, what they and far too many others don’t seem to get – or want to get – is that anisogamy has been around for about billion years, and that there are probably thousands if not millions of entirely different “developmental pathways” and “evolved reproductive anatomies” associated with, that correlate with the functions of being able to produce either sperm or ova. They simply refuse to face or even try understanding basic foundational principles, notably that of taxonomy, “the scientific study of naming, defining (circumscribing) and classifying groups of biological organisms based on shared characteristics.”
https://en.wikipedia.org/wiki/Anisogamy#Evolution
https://en.wikipedia.org/wiki/Taxonomy_(biology)
Kind of think that the characteristic or trait of anisogamy, of the ability to actually produce either of two morphological distinct gametes is that which is shared by the greatest number of organisms, and over the greatest span of time and evolution. Which should thereby be – and currently is – the basis for the most rational and useful definitions for the sexes, male and female.