Gender being a psychological identity, there are as many genders as people can imagine. In a sexual species such as homo sapiens, however, there are only two sexes. This biological truth is one of the most dangerous things to say due to the anti-science scientism popular now, but it must be said, perhaps especially because of that.

In his definitive piece, In Humans, Sex is Binary and Immutable, Georgi K. Marinov explains how people have confused sex and gender, the nature and purpose of sex, and why so-called “Intersex” conditions do not invalidate the sex binary:

Unfortunately, confusion and misunderstanding reign when it comes to their existence. Humans are indeed born with a variety of “intersex” conditions at low frequency, but that does not mean that these conditions are part of normal healthy variation. Humans are also born with a great variety of devastating congenital deformities and diseases, and if alien exozoologists were to write a description of Homo sapiens based on extensive observations of the population, such a description would never feature, for example, anencephaly, and neither would it include anything else but binary sex.

Extremely deleterious phenotypes, especially when their fitness is invariant with respect to environmental conditions, cannot be part of that description, as they are by definition actively eliminated from the population. The mathematics of natural selection is remorseless. For the human population, even an allele with an initial frequency as low as 0.01 and selection coefficient s = 0.05 is nearly ensured fixation. On the other hand, that should not be taken to mean that natural selection is all powerful. First, even if an allele is strongly deleterious, its frequency will not be zero, as it is constantly reintroduced by mutations at some rate µ. Second, alleles with small selective (dis)advantages are not ensured fixation. Genetic drift can lead to fixation of alleles with small selective coefficients irrespective of their effects, as long as s < ~1/N_e (N_e is the effective population size).

Therefore we cannot expect “perfection” from biological processes. Imagine that a biochemical reaction runs with a given accuracy in a finite population. The selective advantage of mutations improving its accuracy will generally be at most the fractional improvement that they confer. Thus it is not possible for selection to push the system towards absolute perfection as further fractional improvements are “invisible” to it if smaller than the selection barrier ~1/N_e. Errors are thus expected to occur everywhere, and indeed they do. This is why important genes get mutated, developmental processes get disrupted, and the results are newborns with very low fitness.

These facts bear on how we are to think about “intersex”’ people. The great diversity of such conditions cannot be explored here in detail. These include Androgen Insensitivity Syndrome (feminization of males due to androgen receptor mutations), Klinefelter’s syndrome (47,XXY karyotype), XX male syndrome (46, XX “males” due to translocation of the master regulator SRY to the X), Turner’s syndrome (45,X0) and many others.

These conditions present with a variety of phenotypes intermediate between typical male and female features, but they have one crucial commonality—individuals afflicted are almost invariably sterile;²⁰ on the few occasions where fertility is possible, the phenotypes are mild and it is hard to even call them “intersex.” Their evolutionary fitness is therefore as negative as fitness could possibly be short of being stillborn (s = -1 for sterile individuals). Importantly, these fitness reductions are invariant to environmental variables. It is possible for a condition that is a debilitating disease under some circumstances to be beneficial under others (e.g. sickle-cell anemia and malaria). But this does not apply to the inability to produce viable gametes, which makes one unable to reproduce under all circumstances.

All “intersex” conditions, when examined, clearly arise from single-gene mutations or chromosomal aberrations on a genetic background that would have indisputably been producing male or female gametes had these mutations not occurred, and, rarely, due to chimerism (i.e. individuals made up of both male and female cells). True hermaphrodites possessing both sets of functional gonads and genitalia have never been observed in Homo sapiens.

Therefore the “intersex” argument against the sex binary is simply not valid. Intersex individuals exist only because of continuous de novo reintroduction of the relevant mutations in the population, recessive genes becoming unmasked, or disruptions of normal embryonic development.

Sex in mammals is on a fundamental level binary and immutable, and claims that “intersex’” individuals disprove that can only be made in the absence of any consideration of the biological nature of humans and how our evolutionary history has shaped our biology. Which brings us to the most worrying aspect of the widespread adoption of such denial.

Sources:  J.P. Van Batavia, T.F. Kolon, “Fertility in disorders of sex development: A review,” J Pediatr Urol 12 (2016):418-425.