Byrne on why sex is binary

At Arc Digital, philosopher Alex Byrne defends the proposition that there are only two sexes, while suggesting that this has no implications one way or the other for transsexuality, gender dysphoria, and related issues.  Let’s consider both claims.
Byrne argues that it is a mistake to suppose that one’s sex is fundamentally a matter of what chromosomes one has or even what sorts of genitals one has.  Hence it is also a mistake to point to examples such as individuals who have male chromosomes but female external genitalia, or people who have only an X chromosome or XXY chromosomes, as evidence against the thesis that sex is binary.  In fact, Byrne suggests, chromosomes and genitalia are reflections of a deeper distinction, and the nature of that distinction is not captured by a mere description of the chromosomes and genitalia: To be chromosomally female is to have the sex chromosomes typical of (human) females; to be genitally female is to have the genitalia typical of (human) females, and so on.  But what is it to be, simply, female or male?
Byrne’s answer is that the sexes are defined in terms of the gametes they produce:
Specifically, females produce large gametes (reproductive cells), and males produce small ones. (Since there are no species with a third intermediate gamete size, there are only two sexes.) A glance at the huge variety of females and males across the animal and vegetable kingdoms will confirm that there is nothing else the sexes can be. For instance, the equation female=XX is confused for a fundamental reason having nothing to do with human chromosomal variation: females of numerous species either have different sex chromosomes (as in birds) or else no sex chromosomes at all (as in some reptiles). The XX/XY system is merely the mechanism by which placental mammals like humans typically become female and male; other animals and plants use different means to achieve the same end result.
End quote.  Byrne does not make use of Aristotelian-Scholastic metaphysical notions in order to make his point, but it is illuminating to do so.  Scholastics distinguish between the essence of a thing and its properties (or “proper accidents”).  A thing’s properties flow or follow from its essence, but are not to be identified with its essence.  For example, the essence of a human being is to be a rational animal, and a capacity for language is a property that flows or follows from this essence.  It is a kind of byproduct of being a rational animal insofar as it will always manifest in a mature and healthy specimen. 
Of course, some individual human beings are deficient in or lacking this capacity, but that is because the “flow” is, as it were, being blocked (by immaturity, brain damage, dementia, etc.).  It does not follow from such cases that the capacity for language is not a true property of human beings, but rather merely that an immature or damaged human being will not manifest all of his properties.  Similarly, the exercise even of rationality itself can be impaired or blocked by genetic defect, brain damage, aging, etc.  For the Scholastic, this does not mean that some human beings are not rational animals, but rather that they are rational animals whose actual exercise of their rationality is being frustrated.
Now, what Byrne is proposing can be interpreted as the thesis that the essence of being either male or female involves having the capacity to produce either smaller or larger gametes, respectively.  And having certain chromosomes and having genitalia of a certain type are properties which flow or follow from having one or the other essence.  In particular, having XY chromosomes, a penis, testicles, etc. are properties of human males, and having XX chromosomes, a vagina, ovaries, etc. are properties of human females.  As with other properties, the manifestation of these can be distorted or blocked due to immaturity, defect, damage, etc.
Again, Byrne doesn’t use such language, but he at least implicitly gestures at something like the essence/properties distinction insofar as he notes that:
There is a complication. Females and males might not produce gametes for a variety of reasons. A baby boy is male, despite the fact that sperm production is far in his future (or even if he dies in infancy), and a post-menopausal woman does not cease to be female simply because she no longer produces viable eggs.
In other words, immaturity prevents the manifestation of the relevant properties in a baby boy, whereas aged organs being worn out prevents the manifestation in a post-menopausal woman. 
This brings us to another Aristotelian notion that illuminates Byrne’s point, viz. that of intrinsic teleology.  As longtime readers of this blog know, intrinsic teleology is the kind that a thing manifests naturally, just by virtue of being the kind of thing it is.  A stock example would be an acorn’s tendency to grow into an oak, a tendency it has simply qua acorn.  This contrasts with extrinsic teleology, which is the kind a thing possesses only insofar as some end or purpose has been imposed on it from outside.  A stock example would be the time-telling function of a watch, which is not intrinsic to the bits of metal that make up a watch, but has to be imposed by the maker and users of the watch.  (Again, see Scholastic Metaphysics for detailed exposition and defense of this distinction.) 
To have an essence involves having certain intrinsic teleological properties.  For example, having the essence of a rational animal entails having faculties that are directed toward or aim at ends such as acquiring knowledge.
Now, Byrne speaks of “the mechanism by which… humans typically become female and male” and says that “other animals and plants use different means to achieve the same end result.”  That is teleological language, and since he is talking about natural kinds rather than artifacts, it is the language of intrinsic teleology, specifically. 
Similarly, when Byrne says that “a baby boy is male, despite the fact that sperm production is far in his future (or even if he dies in infancy),” it is natural to read this in teleological terms.  In particular, it is natural to read it as implying that a baby boy’s physiology is naturally directed toward the eventual production of sperm, and is so directed even if this end is never realized (because of the death of the baby).  Furthermore, the claim that “a post-menopausal woman does not cease to be female simply because she no longer produces viable eggs” can also be read in teleological terms.  The idea would be that a woman’s ovaries are directed toward the production of viable eggs, and remain so directed even if age leaves them no longer capable of realizing that end.  (Something similar is true of organs in general.  For example, the eye is for seeing, and it retains that function even if genetic defect, injury, or old age leave it incapable of fulfilling that function well or at all.)
This reading is especially natural in light of these follow-up remarks from Byrne:
In the light of these examples, it is more accurate (albeit not completely accurate) to say that females are the ones who have advanced some distance down the developmental pathway that results in the production of large gametes — ovarian differentiation has occurred, at least to some extent. Similarly, males are the ones who have advanced some distance down the developmental pathway that results in the production of small gametes.
End quote.  Talk of “developmental pathways” is naturally read as teleological.  The development in question is not just in any old direction, after all, but is a development toward the production of the gametes.  The “pathway” has a specific natural destination.
All the same, I presume that Byrne would not want to commit himself to anything like Aristotelian essentialism and teleology.  He may hold, as contemporary philosophers often do, that teleological-sounding talk is a mere façon de parler which can be replaced with a purely efficient-causal description.  But even the hint of an essentialist and teleological metaphysics accounts for why many with “progressive” views about sex are, as Byrne complains, reluctant to acknowledge that sex is binary.
After all, if anything has teleology, gametes do, and it has to do with getting together with the gametes of the opposite sex.  And if, as Byrne’s account suggests, chromosomes and genitalia play a secondary role relative to gametes, it isn’t hard to figure out their teleology too.  It has to do with facilitating the getting together of the gametes of the opposite sexes.  Hence the extremely well-known suitability of penises to get male gametes into the vicinity of female gametes, etc.
Before you know it, the evolutionary psychologists will show up and start pointing out that psychological drives (like sexual arousal, romantic attraction, and the like) are no less plausibly described in functional terms than genitalia are, and that the psychological functions in question have to do with facilitating the physiological processes by which male gametes get together with female gametes.  Add Aristotelian essentialism and teleology to the mix, and the function talk takes on normativesignificance.  Deviations from the physiological and psychological functions in question take on the status of malfunctions and deformations, no less bad for the organism than other malfunctions and deformations are.  All that’s left at that point is for the natural law theorists to come along and draw out the implications for sexual morality – though the progressive will by that time already have started hyperventilating, in a most unsexy way.
So, the skittishness of some progressives about acknowledging that sex is binary is understandable.  The messier sex can be made naturally to seem, the easier it will be to resist natural law conclusions.  But again, Byrne holds that to acknowledge that sex is binary should give the progressive nothing to worry about.  Is he right?
Well, if essentialism and intrinsic teleology are rejected, then the moral conclusions the progressive dislikes won’t follow.  (Though only because no moral conclusions about anything at all can survive the abandonment of essentialism and teleology, or so I would argue – but that is a topic for another time.)  And as I have said, I presume that Byrne would reject them, though this is not a topic he addresses.
The trouble is that it is very difficult at best to reduce or eliminate essentialist and teleological notions in the context of biology.  To be sure, the assertion that they can be reduced or eliminated is extremely common.  But actually pulling this job off is something no one has really done.  For example, attempts to reduce the notion of biological function (e.g. in causal terms or in terms of natural selection) are famously problematic.  Furthermore, as writers like Marjorie Grene, Andre Ariew, and J. Scott Turner have argued, natural selection in any event at most casts doubt on teleology where questions about adaptationare concerned, but leaves untouched the need for teleological descriptions of developmental processes.  It is often thought that resort to computational notions (such as characterizations of the genome as a kind of software or program) provides a handy replacement for teleology.  But as I argued in another recent paper, the computational descriptions in fact implicitly presuppose something like Aristotelian essentialism and teleology.
Again, Byrne himself describes the phenomena with which he is concerned in terms that suggest teleology.  Even if (as, again, I presume) he would hold that such talk can be cashed out in non-teleological terms, it is another thing actually to show exactly how this could be done.  In particular, one would need to capture everything we know about gametes, chromosomes, genitalia, etc. in a way that makes no implicit reference at all to teleological features.  For example, one would have to be able to give a complete description of male gametes without saying anything that implies that they have the end or telos of getting together with female gametes; one would have to be able to give a complete description of genitalia without saying anything that implies that they have the function of getting gametes together with those of the opposite sex; one would have to give a complete description of immature testicles without implying that they aim or are directed toward sperm production years down the line; and so on.
Since, again, it’s very hard to pull off such a consistently non-teleological re-description (where any aspect of biology is concerned, not just sex), it is no surprise that some progressives prefer to muddy the waters where the biological facts are concerned.  If sex is not binary, then the teleology is messier, and if the teleology is messier, then the dreaded conservative moral conclusions are easier to resist.
So, Byrne’s remarks about the biology are plausible, but his remarks about the implications or lack thereof for progressive views about sex, not so much. 
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