How Sex Happens

From Sex and Intersex. Version 0.5.1

To start, let's briefly review how sex happens. I won't even attempt to start defining what sex is exactly, just the various body parts and processes that we will later associate with an overarching concept. Let's also hold off a moment from intersex cases and just consider typical, non-intersex cases; we need to learn the rules before we learn how to break them.

Genes are divided up into groups called chromosomes and the set of chromosomes has is called the karyotype. A human karyotype has 46 chromosomes.The genes mainly responsible for delegating an offspring as female or male are contained in the chromosomes X and Y. A female has a karyotype of XX and a male has XY, keeping the totals at an equal 46. When we reproduce, our gonads (ovaries in females and testes in males) create gametes (ovum or eggs in females and sperm in males) which have half the chromosomes or the original gonad. A gamete, then, has a karyotype of 23 chromosomes, one of which is an X or Y. An ovum always has a sex karyotype of X while a sperm may have either an X or Y. A fetus is formed when an ovum and sperm come together and combine their chromosomes into a full 46 human karyotype.

The next phase I find fascinating but it is usually skipped in high school biology and sex ed.  For the first seven weeks every fetus develops the same genitals and gonads regardless of genes.  The genitals are shown below.Also, the following website has an excellent, animated diagram of the genital transformation. (Also, the following website has an excellent, animated diagram of the genital transformation.

Notice the two folds of skin are the labia which surround the vagina and urethra in females.  A vagina is not fully developed at this stage but is present as a membrane. The genital tubercle between the labia resembles the female clitoris in location and size. The brain structure is far less dramatically differentiated between females and males but it also resembles a female state more closely. Nipples are also present. By all visible characteristics, the genitals are female. You may have heard the mythic statement that we all begin as female; here it is. Biologically speaking, the human archetype is female.

If the fetus has an XX karyotype, they will continue development along the same path maturing into the finer detail show below.

The Y chromosome is the smallest human chromosome with only 23 genes. It exists solely to change the course of human development from female to male. The famous gene on Y is SRY which activates between the seventh and eighth week. The SRY gene causes a change in the balance of androgens (masculine hormones"'Male' hormones is an unfortunate term, since these hormones are ordinarily present and active in both males and females." (ISNA  I call it masculine because the hormones are gendered: we associate them with males. These hormones are not present on the Y chromosome, only called by it.    ). The body responds to these hormonal balance in the way new tissues grow. The genital tubercle grow larger to become the head of the penis, the urethra (where urine is later discharged) moves from within the labia to the penis head, the penis shaft is formed from a homologous and invisible structure in females, and the scrotum is formed from the labia. An artifact of this transformation is still visible throughout a male's life; looking at the scrotum you can see a soft ridge, the raphe, which marks the fusion of the two labia.

SRY causes a change in the gonads too. They will become ovaries without the addition of androgen hormones. The most visible change is the descent from within the body (near would  the ovaries reside) down into the scrotum, one on each side of the raphe. Sometime between the 16th and 24th weeks a "hormonal wash" takes place over the brain which is responsible for (at least some) of the brain differences between females and males. The nipples remain.

When sex is assigned by a doctor, it is assigned based on the appearance of the genitals and not on genes, hormones or reproductive ability.

All of this is the first of two processes of sexual differentiation. This stage creates the primary sexual characteristics, the genitals and gonads, which are responsible for reproduction. The second stage is more familiar: puberty. During puberty secondary sex characteristics are produced: body hair, fat placement (including breasts), and voice pitch. Both sexes experience greater levels of "masculine" hormones which is responsible for the growth of hair, height, muscle and deepening voice. The reasons this happens more to males is that their androgen increases is greater than females. Reproductive capabilities which were already formed by latent are now active with females ovulating and menstruating and both sexes capable of physical arousal.

I want to emphasize that the development of females and males are not exact opposites, as if mirror images. Rather, all humans begin with female hormones and anatomy. Those with XX chromosomes will continue thusly all their life; those with XY chromosomes will displace their female anatomy and hormones with male. This is why prepubescent males and females are anatomically closer than post-puberty; the prepubescent males are "more female."Not to get off on a tangent, but this is also why pedophile men who are attracted to boys are almost always heterosexual; boys resemble females. The concept of homosexual pedophiles are a propaganda product  The Box Turtle Bulletin features an excellent study on the subject.,002.htm  This goes a long way in understanding the nature of intersex and transgender physiology and the inherent complexity of transgenderism.  It also suggests that the psychology of Leach which interchanges male transgender behavior with female is too simplistic. It also suggests that the gender binary, which states that females cannot become males and vice versa, is already broken every time a male leaves the womb.

Continue: Response of Pro-Binary Organizations