#chromosomes

Human beings typically have 23 pairs of chromosomes with 22 pairs of autosomal chromosomes and typically a pair of sex chromosomes.

The most 'typical' pairings of sex chromosomes are XX and XY which are female and male respectively.

All human beings require an X chromosome to be alive as it contains vital DNA to keep you breathing and actually making you; the Y chromosome is usually the place where the SRY (Sex-determining region Y) gene is located which activates the development of male-like traits when developing in the womb.

The categories of male and female were created to categorize humans into classes that signified their body type. The earliest biologists categorized people by physical traits such as genital and gonadal distinctions and secondary sex characteristics which seemed to roughly correspond to the sexes such as breasts, facial hair, Adam's apples, etc..

Nevertheless, even in ancient times, it was apparent that not everyone could be neatly sorted into one sex and completely barred from being in the other sex.

The term intersex is used for "anomalous" sex traits in people that complicate a clean sex assignment. The prevalence of intersex individuals is up for debate although it is probably somewhere between 17000 to 500 ppm; meaning there are 4.1 million intersex people on the planet at the very least.

The most famous (and relatively rare) type of sex deviations from the typical male-female categorization are individuals capable of producing male and female gametes: occasionally dubbed by the controversial word "hermaphrodite" deriving from Hermaphroditus (the son of Hermes and Aphrodite who had male and female phenotypes).

Intersex individuals labeled "hermaphrodites" suffered tremendous discrimination in many cultures as many ancient peoples saw them as birth defects for failing to fit into a male female binary. Many of the earliest scientists in antiquity asserted that these people must have a "more prevailing" sex asserting that such people needed to be either male or female deep down.

To this day, sex assignment at birth is usually done by a quick physical check of "sex traits" such as genitalia. Nevertheless, the number of births with "ambiguous genitals" is around 500 ppm.

The advancements in genetic sequencing has also indicated that even "unambiguous" sex assignments may not be as clear cut as one might think just looking at an infant's external body.

As I mentioned above the "typical" pairs of sex chromosomes are XX and XY for males and females respectively. This chromosomal basis for sex provided a useful biologically grounded method to allegedly explain why a sex binary exists. This sex classification also seemed to work in nonhuman animals:

However, chromosomal 'abnormalities' were discovered as more and more research began studying chromosomes in humans.

Humans typically have 22 pairs of chromosomes and a pair of sex chromosomes (an X joined alongside an X or Y); nevertheless, there are instances where humans can possess an extra chromosome in addition to the pair known as a trisomy.

The most well known trisomy is Trisomy 21 which causes Down Syndrome:

Down Syndrome and other trisomy conditions like it are called autosomal trisomies as they affect the autosomal chromosomes (the 22 non sex chromosomes).

Autosomal trisomies are either fatal to embryos or cause notable lifelong physical symptoms. In contrast a trisomy or polysomy of sex chromosomes may be either mild or outright undetected until a karyotype is done.

Every human being needs an X chromosome to fully develop past a embryonic stage in the womb. Moreover, the Y chromosome also has the SRY gene which triggers a little later in embryonic development to start development of "male" sex traits.

A child with a single X chromosome in some or all of its cells has Turner syndrome. For those with only part of their bodies having a single X chromosome (this is called mosaicism), they may either be male or female. Those with all single X cells are always female. Those with Turner syndrome are more susceptible to heart problems and diabetes.

Klinefelter syndrome is one of the more common chromosomal abnormalities where an individual has a Y chromosome and 2 (or more) X chromosomes. Although it is not usually noticed until puberty, those with Klinefelter syndrome may exhibit atypical 'male sex traits' during puberty which can often lead to these people being social stigmatized for failing to meet a normative male body type.

In contrast, XYY syndrome is almost undetectable without karyotyping. The majority of the symptoms include a greater risk of learning problems or having physical abnormalities such as a taller height when compared to their parents or ailments like severe acne, asthma, or tremors.

The categorization of people into a clean sexual binary gets really dicey the more one looks at chromosomes and physical characteristics. The modern consensus among biologists is that sex is a bimodal distribution where the vast majority of people can be roughly sorted into two big bens, but there will always be some that cannot be fit into one bin or both bins without several caveats.