The conflation of gender and sex continues, so that the two are often used as if they were synonyms (e.g., the statement “gender and sex both form a continuum/spectrum”). I was thinking about clarifying my own usage of these terms, and thus offer these definitions, which are tentative, for reader comments. I intend these to apply only to humans, though in other multicellular organisms they also apply widely though not universally (for example, many plants and some worms are hermaphrodites with functional gametes of both types, and might be considered a third “sex” because they’re cross-fertile with either males or females—or sometimes themselves).
Again, I offer this for readers’ comments; they aren’t yet my own final definitions. I say this because the subject is touchy and though I want to be biologically accurate, I also want to be civil. And we should recognize that there are diverse definitions of the terms below, though nearly all biologists adhere to the gametic criterion for “biological sex.”
So, here goes:
Sex: Classes of individuals in a species that have the potential to fuse their gametes with those of individuals from a different class, producing a zygote.
Humans (like all mammals and most metazoans) fall into two classes:
Biological Male: Individuals having the capacity/biological equipment to make small, mobile gametes: sperm.
Biological Female: Individuals having the capacity/biological equipment to make large, immobile gametes: eggs.
Under this definition sex is based on gamete type, which nearly always (but not always) correlates with chromosome type or bodily morphology (e.g., secondary sex characters like breasts and body hair). For example, some individuals with Turner syndrome (XO females, lacking one X instead of the common XX females) can make eggs and become pregnant), while some males with Klinefelter syndrome (XXY rather than XY) have motile sperm, though most are usually sterile. Regardless, these individuals fit into the biological “male” or “female” categories above, and do not constitute new sexes.
Likewise, many individuals with ambiguous genitalia can nevertheless make viable sperm or eggs, and thus fit into one of the two classes above.
Under this definition of sex, nearly all individuals fit into a biological sex binary, as there are only two gamete types. There are not three or more types of gametes seen in humans. Thus we can say that assignment to a biological sex is binary, and that biological sex does not form a continuum (though gender does; see below). There are a very, very exceptions that I detail below, but no individual makes gametes other than sperm or eggs, and no individual makes more than one of these types.
There are also individuals with “disorders of sex development” (DSD) who, due to various biological anomalies, physically resemble members of one sex (i.e., they have the genitalia and/or secondary sex traits of males or females), but lack the capacity and equipment to make viable gametes. Rare individuals with Androgen Insensitivity Syndrome, for example, have the XY chromosome constitution of males but are insensitive to testosterone and other male sex hormones. Most of these are born with female genitalia, but some with male genitalia, and genitalia are often atypical. They usually have female versions of secondary sex characteristics. As they lack the capacity to produce gametes, one could say that they could be seen as belonging to the following two classes based on appearance. Note that these classes are based on phenotypes rather than gametes:
Phenotypic Male (individuals with genitalia or secondary sexual traits of males, but which lack the ability to make sperm).
Phenotypic Females (individuals with genitalia or secondary sexual traits of females, but which lack the ability to produce eggs)
We are not referring to prepubescent individuals or postmenopausal females here, which can be considered biological males or females because they had the evolved equipment to produce eggs or sperm, but didn’t use the equipment to produce offspring or had minor developmental problems that rendered them sterile (e.g., very low sperm count). Do remember that there will be rare exceptions to any generalization, or caveats like, “What about women after they go through menopause?”. but that is not the issue that the whole sex/gender kerfuffle is about.
Alternatively, as does Sax (2002; see below), these “phenotypic” classes could be counted as intersex. But they do not constitute new and different biological sexes.
There are also cases of hermaphroditism in humans: individuals who produce both ovarian and testicular tissue. Only about 500 such individuals have been described, with no more than 11 individuals being fertile, but fertile as only either males (producing sperm) or females (producing eggs). (As far as I know, we need more data on these individuals.) Those hermaphrodites who produce viable gametes could be regarded as biological males, and those with viable eggs as biological females. The rest of these individuals, since they produce no gametes but have tissue associated with production of both types of gametes, could be seen as intersex. While their appearance could slot them into the categories of phenotypic males or phenotypic males, they are again not members of not a “third sex”.
Sax estimates the frequency of these true intersex individuals as 0.018%, or one individual in 5600. Even if all individuals’ sex were plotted on a frequency graph, about 5999 out of 6000 individuals would fall at the “biological male” or “biological female” modes, with the few exceptions being intersex (or, if you wish, “other”). This means that biological sex is effectively a binary and not a spectrum, since exceptions to the first two classes given above are vanishingly rare.
Gender, however, is different. I see it as the “sociosexual role assumed by an individual”, that is, where an individual sees themselves as fitting on the spectrum of sexuality of male or female, a position that is self-determined and self-defined. Many of the behavioral “sex roles” of males and females that are seen as “typical “(difference in body size, aggression, sexual “pickiness”, and so on) were molded by sexual selection over millions of years, and many are seen in our relatives.
Note that, since some people identify as partly or fully animal (see here for an example), they need not fit within the spectrum of human sexuality. Most, however, do, and the huge variety of sociosexual roles does mean that, contra sex, gender does form a spectrum. There is an infinite number of ways to combine “male-typical” and “female-typical” traits, as well as inventing new traits.
Because I see gender as being fundamentally different from biological sex, this causes a problem for using terms “transgender” and “transexual”.
Humans, unlike clownfish, cannot change their sex, so they cannot really be transsexual—not in the biological sense.
On the other hand, a biological sex does not absolutely stipulate a given sex role or gender; sex-associated behaviors and appearances are variable. This means that a biological man who adopts or evinces some phenotypic or behavioral aspects of a woman cannot be said to be “transgender”, either, for sex is not gender. Such a person is assuming a gender not usually associated with their biological sex, but there is no diagnostic difference in behavioral or most morphological traits of biological sexes. Thus biological men can be aggressive or not, sexually promiscuous or not.
There are, however, behaviors and phenotypes more associated with human males than with females, and vice versa, with many of these differences due to natural selection.
Because of this, I would prefer to use the terms “transgender” than “transsexual”. This is simply because it’s impossible to change one’s biological sex, but at least tenable to change behaviors and phenotypes typical of one’s biological sex to behaviors and phenotypes typical of the other sex. Thus, a biological female who has a double mastectomy, takes hormone therapy, and has a phalloplasty operation to construct a penis is not changing biological sex, but assuming secondary sex phenotypes of biological males. I would see such individuals as “transgender” rather than “transsexual.”
I welcome comments, questions, and clarifications here. What I’m trying to do is find some terminology that would avoid the conflation of “sex” with “gender”: a conflation that is not only leads to misrepresentation of biology, but also results in people talking past each other.
Sax, L. 2002. How common is Intersex? A response to Anne Fausto-Sterling. J. Sex Research 39:174-178.