• Jessica Evans

Why biology isn't binary


We live in a binary age. You’re either a gay or straight, right or wrong, boy or girl. Nature is not binary. Humans have introduced the concept of binarism. You may be thinking “but wait, even in nature there is male and female – what are you on about now?” Well, my friend, it’s time to learn about intersexuality.

Intersexuality is found in humans, and also cats, pigs, goats, dogs, cattle, snakes, worms, snails, and amphipods. And the physical expression of female and male sexes is common in fish. So it really is no stranger to nature. In fact, intersex people are as common as red heads!

To understand intersexuality you need to understand the difference between sex and gender. Sex is the physical aspect – the physical manifestation of male or female, while gender is the psychological aspect – whether or not a person feels like a boy, a girl, somebody in between, or neither.

A person is typically assigned a gender at birth based on the external expression of their sex, their genitals. A person is a boy if they have male genitals, a girl if they have female genitals, and they are brought up as such.


Intersex people are included in the queer community because they can experience marginalization and may often question their gender identity (this is not always the case). This is the intersex flag designed by Organisation Intersex International Australia.

Chromosomes are bunches of DNA inside your cells. Humans typically have a set of 23 pairs inside each cell. Biological sex can be determined by one of these pairs, creatively named sex chromosomes. These chromosomes are in charge of assembling all the tissues that make a person male or female.

For humans, an individual with an XY chromosome is male, and an individual with an XX chromosome is female. Pretty simple concept, but also pretty binary. A person who is intersex is biologically different to simply XX or XY, female or male.

These differences might be visible, like the presence of both breasts and male genitalia, or the presence of both a vagina and testes and many other combinations of what are either typically female or male.

The characteristics of intersex people can also be invisible, in the form of only chromosomal differences.

Some intersex people have an XXY chromosome instead of the XX or XY associated with non-intersex people. Some people may have an XO chromosome, XX-XXY chromosome, XX-XY chromosome, or an XX-XO chromosome.

Each variation of the sex chromosomes results in a different variation of physical characteristics like specific sex hormones, breasts, and genitalia.

Changes to genitalia can also be caused by hormonal influences on a foetus in the womb. Female rats kept near a male rat whilst in the womb have demonstrated male-like behaviour and more masculine-appearing genitals.

In the end, sex exists on a spectrum, just like hair colour, height, and sexuality. Nature knows no binary. After all, it gave us the rainbow – how is this really any different?

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©2018 by Bite-sized Sci | Jessica Evans