The one-celled, slipper-shaped animal we know as Paramecium can live alone, dividing into two when it is time to reproduce. When opportunity allows, a Paramecium will pair with another Paramecium and mate, trading substance of their selves. But pairing is not haphazard. There are over half a dozen different “mating types” of paramecia, and only certain pairings are possible. Sex, in paramecia, comes in more than two distinct forms. Are we humans more like paramecia than we thought?
Before birth (prenatally), sexual differentiation in humans always follows a specific sequence: first, genetic sex is established; second, development of gonads (under the influence of genetic sex); then, differentiation of the internal genital duct structures and finally formation of external genitalia. Recent, very tantalizing evidence suggests the embryonic brain may go through some degrees of sexual differentiation through control mechanisms not yet understood. Further, the influences of hormones on the central nervous system may have an effect on hormone secretion and sexual behavior even in adulthood.
Specifically: how does one decide upon the sex (as distinct from gender, which is the sex one believes oneself to be) of a newborn? What are the indicators we use to tell us whether an infant is male or female?
Most obvious to an examiner are the external genitals—penis or clitoris, scrotum or labia. But penises can be small, clitori large, a scrotum incompletely fused or labia partially fused. Abdominal surgery (laparoscopy or, less commonly, laparotomy) can establish whether the child possesses ovaries or testes, but it happens that some individuals have organs with characteristics of both an ovary and a testis. The sex chromosomes were long thought to be a decisive indicator, either XX or XY, though pathologies associated with extra chromosomes are now well known. We now know that mosaicism is also not uncommon: a condition wherein some cells possess two X chromosomes, while others are XY. Hormonal assays are not only equivocal but are so variable as to be essentially useless in determining either sex or gender: most recently noted in the case of the young sprinter, Dutee Chand, a female in all respects except for masculine levels of testosterone. Indeed, only the (arbitrary) sex of assignment is unequivocally male or female.
What is paradoxical is that not all disparities between gender and sex can be attributed to any clearly identifiable causes, whether pathological or not. There appears to be no inevitable concordance between many of the physical indicators and gender. As in the case of Chand, the individual may have levels of testosterone corresponding to those of a male and yet appear female in all other regards. Many other possible combinations of indicators have been seen. Estimates of the frequency of these conditions vary, possibly because many subjects were self-selected, usually as the result of some other underlying pathology, not necessarily connected to their morphology. However, the numbers are sufficient to allow the conclusion that sexuality should not be regarded as dichotomous: either male or female. Not only are there variations in each of the six to eight accepted markers of sex, but the variations are not always concordant. We might well recall the single celled Paramecium. It has no less than eight different mating types, or “sexes,” some of which can pair with only particular other types. The type of sex an individual is depends on which criteria one selects. Each of those criteria, in turn, seems to exist in a different space. Sex and thus gender, the sex we chose to be, comes in more forms than previously imagined—certainly in more than two!
In summary, “sex" has referred historically to a division of humans (and, for that matter, most other animals) into two classes: females, who are generally able to produce ova (eggs), and males, whose sperm serve to fertilize these eggs. In most cases, there are physical differences associated with those two discrete functions. In humans, these include (usually) breasts, vagina, ovaries and other, associated, structures in females and penis, scrotum, testis, et al for males. Not every individual necessarily possesses all of the attributes of one sex or the other, but, for the most part, the division into males and females has seemed unproblematic. Until recently…
“Gender,” on the other hand, is a social construct that refers to behavior that is associated with one or the other sex. A Google search quickly offers up that gender “… refers to the attitudes, feelings and behaviors that a given culture associates with a person's biological sex.” An alternate useful definition is frequently “the sex that one believes oneself to be.” There is no necessary link between one’s gender and one’s sex as defined in terms of reproductive competence
In recent years, the gender one could adopt has increased from merely two, feminine or masculine, to multiple, less categorical options, not always clearly defined. Thus, we have added bisexual, transsexual, gay, lesbian and yet others to the list of possible genders, and their relation to biological sex is not fixed. One supposes that there are limits and that there may be reasons why certain possibilities or combinations thereof are not possible; and yet, the cosmos we consider is so much vaster than we’d have believed less than 50 years ago—might it not be even larger still than what we imagine now?
The visible horizons of our scientific, social, and humanistic knowledge regarding what was once believed to be a very simple scenario—assignment of sex and gender—have expanded rapidly in the past 50 years. We now consider a thrilling and uncharted frontier for further understanding the possibilities of human sex and gender, where uncertainties are multitude and absolute rules seem to be few. The tantalizing prospect of new knowledge to be gained can be shared alike by scientists and poets, psychologists and playwrights, as well as all of humankind because is there anyone whose life could not be touched by these questions?
Peter Klopfer, Ph.D., is a Professor Emeritus in the Department of Biology. Gerard Honoré, Ph.D., M.D., received his doctorate degree from the Department of Physics in 1986.
Get The Chronicle straight to your inbox
Signup for our weekly newsletter. Cancel at any time.