Sexuality isn’t a “spectrum”, it’s a “gamut”.

matt harbowy
Jul 23, 2017 · 10 min read

First, let’s talk about the nature of the word, “spectrum”.

You can see exactly three colors: reddish, greenish, and bluish.

image from What kind of color reception is important?

When someone talks about a spectrum, they are often talking about something which has discrete components, but because those discrete components mix in different quantities, the overall perception of discrete values is better understood and interpreted as a spectrum. Even if some people have only two sensors for color, they also perceive a spectrum. It’s only when you have a single receptor that you see things in black and white.

image from Colorblindness (A Helpful Guide)

Let’s talk about the birds and the bees: you know, sex.

image from Sex-determination system — Wikipedia
  • In birds, sex is determined by the females- a female has chromosomes ZW, and a male has chromosomes ZZ.
  • In the bees, there is no sex determining chromosome: females are diploid, and males are haploid.
  • In many other insects, there is no male chromosome- the females are XX, and the males are XO.
  • In humans and most other mammals, the males have the sex determining chromosome, XY, and females are XX.
  • In platypuses and other monotremes, there are five pairs of sex determining chromosomes, some resembling XY, and others resembling ZW.

Let’s also talk about how gender gets assigned to a human being.

At a first level of understanding, you have to understand that in humans and many of the mammals, the actual equipment for assigning gender isn’t located on the sex chromosomes. There’s a somewhat critical piece of the puzzle, called SRY, which produces a protein that binds to DNA and alters a critical balance in gene expression that encourages development of male-equipment (penis and testes) or encourages female development (ovary and uterus). Fundamentally, though, if you go back and trace the individual cells as the blastocyst differentiates into a fetus, you’ll see that the cells that become a penis or testicles and the cells that become an ovary or uterus are in fact the same cells. In both men and women, the formation of the cells involved in reproduction involve the same biochemical process: they both undergo meiosis, and so, from a “nuclear” perspective, the actual engineering of a sperm or an ovum is governed by exactly the same set of proteins and enzymes and regulatory systems. Around that nucleus, however, there are a completely different set of systems that engineer the flagellum-like tail of the sperm or the cascade mechanisms of the ovum that accept the nuclear material of the sperm. Here’s the trick, though: women have all the genes and protein expression systems needed to make both sets of assemblies.

Now, let’s talk about what happens. (adapted, in part, from How many sexes are there in nature?)

image from Sex-determination system — Wikipedia

The most commonly known sexing system is the XX/XY sex determination scheme, widespread in the animal kingdom.

Biology is typically taught that males have (a) unique gene(s) only found on the Y chromosome (generally through the SRY gene) that give rise to maleness. However, the major development genes for genital/sex organ and secondary sexual characteristics are located on other chromosomes, and depend on a poorly-understood chain of expression to determine maleness or femaleness. This includes such genes as 5-alpha reductase, located on chromosomes 2 and 5, but involves many others. Testosterone and cortisol, produced by both men and women, have an effect on expression, and there are many known variations observed. For example, Wikipedia says: Sex determination and differentiation (human)

The following disorders are caused by a malfunction in the sex determination and differentiation process:

Congenital adrenal hyperplasia — Inability of adrenal to produce sufficient cortisol, leading to increased production of testosterone resulting in severe masculinization of 46 XX females.

Persistent müllerian duct syndrome — A rare type of pseudohermaphroditism that occurs in 46 XY males, caused by either a mutation in the Müllerian inhibiting substance (MIS) gene, on 19p13, or its type II receptor, 12q13. Results in a retention of Müllerian ducts (persistence of rudimentary uterus and fallopian tubes in otherwise normally virilized males), unilateral or bilateral undescended testes and sometimes causes infertility.

Male pseudohermaphroditism — Failure of androgen production or inadequate androgen response, which can cause incomplete masculinization in XY males. Varies from mild failure of masculinization with undescended testes to complete sex reversal and female phenotype (Androgen insensitivity syndrome)

Swyer syndrome. A form of complete gonadal dysgenesis, mostly due to mutations in the first step of sex determination; the SRY genes.

It is thought that the SRY gene on the Y chromosome arose from an inversion of SOX3, located on the X chromosome. There are 20 SOX genes in humans, and all produce similar kinds of proteins that have some form of role in development of sex. In addition, the evolution of the SRY gene and the Y chromosome shows that SRY contains a series of eight palindromes

Abundant gene conversion between arms of palindromes in human and ape Y chromosomes

These palindromes function to protect and repair the Y chromosome, and allow for recombination within the Y chromosome in much the same way that pairs of other chromosomes recombine. Furthermore, the palindromes an sequence inversions occurred multiple times during our evolution from our ape-like common ancestor.


Right about now, you might be saying, well, what you’re talking about is “defective” individuals, and therefore has no relevance to the biology of “normal” individuals. That’s an entirely fair but misguided criticism, and here’s why.

All people start out, more or less, with the “complete set”, except in extremely rare cases where a gene is deleted. In that complete set are often multiple copies of the same information, so even if one or the other set becomes damaged in translation, there are backups and redundancies. The line between a fatal and a non-fatal mutation is not necessarily well understood, but the difference between two otherwise “normal” mutations is even less well understood. As biological researchers, we use the existence of clearly differentiable phenotypes, often separated into “wild-type” (that which is associated with normal, “natural”, “in the wild” variation) and “mutant” phenotypes, but in fact all variation in the wild was at one point or another “created” by a mutation, and as we sequence the genome of more and more individual humans, we are beginning to resolve the genetic history of those mutations. When a “mutant” arises, there’s often a specific locus on the genome that associates the “mutant” phenotype with a specific genotype. It’s somewhat helpful to see the creation of “pathological mutants”, because it becomes a way to label the gene in the genotype for the “wild type” phenotypes with an obvious function.


Think about, say, 5-alpha reductase, or testosterone, or estrogen, or progesterone. Both men and women have all of those hormones- if a woman wasn’t able to produce testosterone to some extent in some of her cellular systems, it’s very likely that she wouldn’t be able to survive. Both men and women produce varying levels of each of those hormones in different parts of their body. Overall, as an “average”, though, we say that women have an abundance of “estrogen”, since overall, they have more cells that produce estrogen in abundance, and we say that men have an abundance of “testosterone”, since overall, they have more cells that produce testosterone in abundance. But also, too much is not a good thing either: both men and women can have too little or too much of either, and the end result is clearly biologically obvious, but when you start talking about so-called “normal” people and measuring their levels, you begin to find that the numbers are not absolute set points, and they vary wildly between otherwise “normal”, so called “wild-type” specimens of humanity.

In fact, of the dozens of hormones and proteins/enzymes and gene expression systems, you see a nearly infinite gradient of possibility.

This is why it is more sensible to talk about gender and gender expression and identity as existing on a spectrum, rather than two binary choices. In fact, if you’re going to talk about the spectrum, calling it a straight line between male and female itself is a deeply misleading way to represent gender identity. To figure that out, let’s return to our analogy of color representation.


when talking about color, it seems perfectly clear that there are (in so-called “normal” individuals) three color receptors. So, you might think that having three variables, red, green, and blue, might allow a computer system to reproduce any color that could be visually expressed and seen by people. Not so fast! In fact, you don’t.

image from Better Color And Adobe RGB Performance — Apple’s iPad 3, Part 1: The Complete Retina Display And A5X Review

In fact, when trying to reproduce a color on a piece of paper or on a computer monitor, you often aren’t talking about using matched sets of chemicals, where the red phosphor of a television screen and the red receptor of the eye are exactly one-to-one in correspondence. As a matter of practicality, it isn’t possible to do so, so when we talk about color and the color space, we talk about the color gamut: the actual range of colors that can be expressed by any one system.

In some kind of deep irony or coincidence, the gamut of color can be expressed in near-totality by exactly two variables, which in the CIE system, coincidentally, has values on the X and Y axis.

image from Gamut — Wikipedia

Because there’s a very subtle difference between the red and the green receptors of the eye, and because the green receptor plays such a dominant role in vision (being involved in both color perception and night-vision perception), there’s an outsized contribution to color that creates the bulge in the spectrum representation above near 520 nm, at about 1.0 on the Y axis and 0.0 on the X axis.


Back to gender. When we talk about gender and sexuality, we are talking about a whole series of expressed traits, a gamut of sexuality that is not a straight line from male to female, but a series of overlapping domains and responsibilities. Unlike color though, where there are only three receptors, there are 20 SOX genes, as mentioned before. Why wouldn’t you expect the diversity of possible expressions of sexual identity and differentiation to be even more complex than that of color?

Unrelated to SOX: we might say, for example, during one era, that a firm set of breasts or buttocks might be a “desirable” characteristic for a female of the species, but having a good combination and pleasing balance of lipid-containing tissues and muscle containing tissues involves adipocytes and myocytes, both of which are possessed by either gender. Men can have “a nice rack”, pleasing muscular six-pack abs, but so can women. In fact, the sets of secondary sex characteristics that might be influential in sexual selection change over time. What is pleasing today might be different from 100 years ago, and entirely different from 1000 or 10,000 years ago.

I think that’s a politically charged and unnecessarily limiting way to express the true nature of sexual identity.

I don’t expect it to catch on, but I think I’m personally going to stop using the term “sexual spectrum” and use, instead, “sexual gamut”, to better reflect my own understanding of the many forms of sexual identity that is expressed by different people. If I were to see, say, an entirely new sexual identity: say one that is based entirely on a flushed-face response to cilantro, to make up a somewhat absurd example, I’d be completely fair in saying that this isn’t something abnormal, it’s just not in my usual gamut of sexual identity. Just like Adobe products use the Adobe RGB gamut of color, I’d be hard pressed to try to use an Adobe product to try to reproduce a color outside of its gamut, and I shouldn’t be trying to understand the entire gamut of sexual response and expression on a limited palette of sex gamut using say, Freud’s gamut, or Masters’ and Johnson’s gamut, or Kinsey’s gamut.


for more on the subject, see The XX & XY Lie: Our Social Construction of a Sex and Gender Binary by Sara C.

see also: Beyond XX and XY: The Extraordinary Complexity of Sex Determination, SciAm, Sep 01 2017.

answer originally published on Quora: Why do some people say there are only men and women, while others say it’s a spectrum?

matt harbowy is a scientist, activist, and data management expert. He is one of the founders of the non-profit Counter Culture Labs, working to bring fairness and egalitarian ideals to people interested in learning about science and biotechnology. He is also a top writer on the question and answer site, Quora.

matt harbowy

Written by

no job too dirty for the f*%&ing scientists. --Burroughs

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade