Biological Sex and Sex Differentiation

First of all, an important question: why study biological sex qua biology? My take on this is that while it is relatively easy to believe that gender is culturally influenced, socially constructed, or even purely performed, on the other hand biological sex is often considered to confer baseline naturality to the difference between males and females. Investigating biology can shake up what naively seems to be a very real binary, ultimately denaturalizing even this most basic human dichotomy.

I. What are Male and Female?

The assignment of a male and female sex is only biologically meaningful in sexually reproducing species where organisms produce two different characteristic gametes (germ cells or sex cells made through meiosis, these are haploid, meaning they only possess half of the genetic complement). In such species, the female is the organism which produces the larger sex cell, while the male's is smaller This means that for species which don't reproduce by combining gametes, or those for which the gametes are mainly identical (isogamous species), male and female are not defined. In some sense, then, women are biologically constituted by association with that part of the species which produces eggs, many times the size of sperm.

II. Animal Sex and Cultural Baggage

Because of the larger size of the female gamete, it is in general less mobile than its male counterpart. This often, but not always, corresponds to a bigger female role in gestation. This sometimes leads to a more active female role in early child-rearing. Mammals, male and female, have sexually sensitive tissue which typically develops into either an imperforate (no holes) clitoris, or into a larger organ, the penis, which carries the urethra in males.

Two-Sex Species

• SPOTTED HYENAS. In this species, male and female have genitals which are externally indistinguishable. They have an important social role: hyenas recognize one another by sniffing penises. Both are erectile. However, the female penis is highly elastic, and both sex and birthing occur through the penis (rather painfully for the female). Hyenas are also one of the few species of canids which, in the human biological literature, are considered to be female-dominant, a fact which many commentators have linked to the presence of female penises. (Stephen Jay Gould on hyenas)
• REEF FISH. Most species of reef fish, and several others, are capable of one or several changes of sex in their lifespans, both protogynous (male-->female) and protoandrous (female-->male). Though the examples are very diverse, there is one species that has gotten disproportionately much attention: the Cleaner fish (Labroides dimidiatus) travels in groups which appear to have a single male at a time, which fertilizes eggs for all the females. When the male dies, a female from the group changes sex and assumes the male role. The typical term used by the fish biologists for their living group is a "harem," and the male is presumed to hold "complete dominance" over the females. In fact, in an influential paper in the 1970s, D.R. Robertson opined that, "The ultimate ambition of female Cleaner fish is to become male." (fish references)
• SEAHORSES. The male becomes pregnant and carries the young to term. The female has no role in gestation.
  "Before mating, the male seahorse changes his coloration and dances around the female every morning for three days (known as the "morning greeting"). On the third day, the male twists his body to signal that his pouch is empty, and with slow movements the female moves her head up and down in a signal of approval if she is willing to mate. Then the two dance belly-to-belly as the female transfers as many as 1000 eggs to the pouch of the male. The male fertilizes them inside his body and carries them for a gestation period of two to three weeks. Each larvae has its own tissue pocket and gets nutrients and oxygen from the male bloodstream. The embryos' development is regulated by the reproduction hormone prolactin (also found in female mammals). At the end of the two- to three-week period, he goes into a series of contractions and gives birth to tiny, fully-developed juvenile seahorses that are exact scale replicas of adult seahorses." (reference)
• APES. There are four non-human species of ape: chimpanzee, orangutan, bonobo, and gorilla (gibbons are sometimes included as well). As these hominid primates are the closest evolutionary relatives of humans, much has been made of their sexual behavior. Gorillas and orangutans display extreme physical dimorphism, with males up to twice the size of females. There are a few notable features of ape sexuality which bear mention here. First, it is well-documented that rape, or observably forcible sex, is common among orangutans. In fact, it most frequently is carried out by so-called arrested males, young males in whom puberty is deferred, sometimes for decades. It seems that orangutans have some control over the hormonal onset of puberty, for arrested males are frequent when dominant adult males exist in a social group. Second, bonobos carry out many sexual activites that are distinctly non-procreative, including oral sex, homosexual activity, and face-to-face sex (the latter is very rare among non-human animals). Bonobo sex

Wholesale Projections of Sex

• E. COLI. With E. coli and in other bacteria, the F+ plasmid and F- plasmid are identified by whether they are donors or recipients of genetic information; on this basis alone, they are called "male" and "female" respectively, as documented by Bonnie Spanier.
• ELECTRONICS. Those connections with appendages are called "male"; those with holes, "female."

III. Human Sexual Differentiation

Through six weeks, the human fetus is undifferentiated with respect to sex ("sexually indifferent"). It has two sets of tissue that may or may not become activated, the Mullerian ducts (which have the potential to become female internal organs-- uterus, fallopian tubes, etc) and the Wolffian ducts (which may become male internal organs-- seminal vesicles, vas deferens, epididymis) Between the sixth and the eighth week, the fetal body starts to produce mass quantities of many hormones. [It's important to note that a hormone, by definition, is any chemical, organic or synthetic, which travels in body fluid, usually the bloodstream, and regulates cellular physiology-- this is very broad! The most famous hormones are only a few of a dizzying array that has so far been identified.]

The egg carries an X chromosome, the sperm either an X or a Y. Thus, typically, fertilized eggs have either XX (female) or XY (male) as a karyotype (sexual genotype). In standard XY development, at the 6-week stage, the Y begins to express: testosterone is secreted along with MIS (Mullerian Inhibiting Substance). There are many related structures and compounds: SRY is the name of the gene that triggers the production of H-Y antigen, which has a role in testicular development; DHT (dihydrotestosterone) is the specific testosterone derivative that governs development of external genitals in males. What has been noted by feminist biologists at least since the 1980s is the total lack of study of the female chemical pathway. Estrogen and progesterone are present in fetal development as early as testosterone, but are not considered to have an active role in morphological development. Note that all three are extremely structurally similar members of the cholesterol family, and that both males and females typically produce all three in non-negligible quantities.

In utero, that is, in the womb, the fetus is exposed to a rich soup of hormones, and in most cases the dimorphism of male/female development is approximated fairly closely. The second major round of hormones happens on time-release some years later: puberty. At this time, people are exposed to a blitz of hormones that induces rapid further sexual development, along with secondary sex characteristics like body hair, voice change, breast growth, and menarche (beginning of menstruation).

IV. Intersexuality

Because the chemical pathways of sexual differentiation are so intricate, there are many developmental turns possible within the standard XX/XY karyotypes. Here is a short collection of biological possibilities.

• AIS (Androgen Insensitivity Syndrome)-- here, your genotype is XY and your hormonal balance is typically male. However, there are no cell receptors present which recognize and express androgens (testosterone, DHT). The MIS, however, is expressed, so the Mullerian ducts degenerate and the Wolffian ducts develop: this means testicles are present, but undescended. Externally, though, your genitals are female in appearance. You never menstruate. The upper third of your vagina is not present, and there is a possible range from the presence of the lower two-thirds to merely a "dimple" (vaginal hypoplasia). Particularly if a vaginal canal of some length is present, you can go through your life unaware of this condition, living as a woman. This was the case of Maria Patino, a Spanish hurdler who was disqualified from international competition in 1988 after tests revealed her to be XY. (The testers advised her to fake an injury and withdraw; she refused, and after the results were published she lost not only the right to represent Spain but also her university scholarship and her boyfriend.)
• Partial AIS conditions can result in testosterone being produced but not fully expressed.
• 5-ARD (5-alpha-reductase Deficiency; also "Penis-at-Twelve")-- a certain enzyme is responsible for the transformation of testosterone into DHT, which is the mechanism for fetal development of male external genitals. Without DHT, then, you are born with external genital anatomy ranging from typically female appearance to somewhat ambiguous. However, since DHT is not the only mechanism for the physiological effects of male puberty, you undergo "virilization" at the onset of puberty, including in some cases the descension of testicles and the growth to penis size of an erectile phallus. Some 5-ARD individuals, after having been raised as girls, are subsequently considered men and go on to father children. 5-ARD is heritable and is substantially more common in certain gene pools, especially in the Dominican Republic (where people whose sex is seen to shift at puberty are called guevedoces, or penis-at-twelve), but also in New Zealand and Turkey.
• DHT Deficiency-- similar effects to 5-ARD.
• CAH (Congenital Adrenal Hyperplasia)-- here, your genotype is XX, and your initial sex hormone balance is typically female. (Actually, CAH can occur in XY individuals as well, but there it does not cause an intersex phenotype.) However, the adrenal gland does not produce cortisol (a non-sex-related hormone) but instead creates more than usual amounts of the other hormones it controls, including androgens. Thus there is often partial masculinization of the genitals, including a large clitoris and partial closure of the urogenital swellings, so that the labia are incompletely fused into a scrotum. Cortisol is necessary to survival, so in the most extreme cases CAH must be medicated daily. Furthermore, operations are still routinely performed on CAH infants to excise or cut down the "oversized" clitoris.
• AGS (Adrenogenital Syndrome)-- another name for CAH.
• Vaginal Agenesis (related to Mayer-Rokitansky-Kuster-Hauser Syndrome)-- here, an XX baby is born without, or with a very short, vaginal canal. Your uterus may be absent, or unusually small, as well. This condition is still routinely treated with the insistence that teen girls should "create" vaginas through long and painful sessions with vaginal dilators in order to have normative sexual function.

V. Karyotypes

• Mosaicism-- two or more populations of cells in the same individual. That is, not all of your body's cells have the same karyotype as each other, usually caused by a change which occurs in an early stage of mitosis (the repeated splitting of the zygote into more and more cells). For instance, biologists now work under a modification of Mary Lyon's hypothesis which holds that both X chromosomes of a female are not simultaneously expressed-- either the paternal or the maternal X is primarily active, while the other is suppressed to some extent. Since this designation occurs around the 16-cell stage of mitosis, which X is active varies among different cellular populations (say 6 chose the paternal X and 10 chose the maternal X). In this sense, every normal female exhibits a form of mosaicism.
• XX/XY-- the expected female and male karyotypes. Frequency unclear; see rest of this section.
• XO (Turner's Syndrome: 1 in 3000)-- this involves monosomy of the X chromosome; either the second sex chromosome is entirely absent, or it is structurally impaired from being expressed. You are typically considered female. Turner's frequently manifests in mosaic form, so that some cells are XO and others are of a different type (this has been documented as occurring XO/XX, XO/XY, XO/XXX, and in other configurations). Depending on the proportion of body cells with XO type, the phenotype associated to Turner's Syndrome may range from presence of readily detectable features to almost no difference from the norm. In the most noticable cases, you may manifest some or all of these associated features: short stature, low hairline, webbed neck, amenorrhea (no menstruation), and no pubertal development of secondary sex characteristics. (In fact, some degree of Turner's syndrome is believed to be involved in as many of a third of cases of amenorrhea.)
• XXY (Klinefelter's Syndrome: 1 in 850)-- XXY is the most common karyotype, but Klinefelter's encompasses any karyotype with two or more X chromosomes and one or more Y, possibly in mosaic form with other types. You are phenotypically male; at puberty, the sex development produces unusually small testes and often a small penis. Klinefelter's is cited as the most common source of male infertility. Other physical features may include: elongated legs and lower body, low IQ (but rarely retardation), lack of male secondary sex characteristics, and some degree of breast development.
• XYY (1 in 1000)-- here, there is one X chromosome and there may be two or more Ys. In the 1960s, police apprehended serial killer and sexual predator Richard Speck. In his defense trial for the murder of eight nursing students, he claimed that he had XYY chromosomes, which predisposed him to his behavior. There followed a flood of research, early versions of which claimed that these chromosomal conditions predispose men to low IQ, sociopathic behavior, and heightened aggressiveness via heightened testosterone. It is currently considered that all of this research is inconclusive (much of it occurred through testing on prison populations with questionable methodology), and in fact it turned out that Speck himself was not XYY to begin with, but garden-variety XY.
• Multi-X (1 in 1200)-- though relatively frequent, Multi-X appears to have very little documentation (much less, for instance, than the rarer Turner's syndrome). As one medical text says, "Most of these women are entirely normal. ...[T]here is an increased tendency to mental retardation in proportion to the number of extra X chromosomes." This seems to me to need further analysis.

VI. Cultural Sex Regulation

1966: Olympics begin "nude parade"
1968: gene tests
1996: only 4 sports still test (skiing, volleyball, weightlifting, basketball)
1999: sex testing abandoned "unless high degree of suspicion"