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Do Gametes (Egg/Sperm) Create a Sex Binary? Science Confirms No.

Cade Hildreth
Do Gametes Create a Sex Binary

Key Takeaways:

Why Gametes Don’t Create a Sex Binary

Sometimes people who believe in a sex binary—also called binarism—will say, “Gametes create a sex binary.” In humans, gametes are are the reproductive cells, which can be:

While this is a common misunderstanding, it misses two major points: First is that no gametes can be present, along with ambiguous gonadal tissue. In humans, gonads can be:

This third possibility of ambiguous gonads coupled with no gamete production clearly defies the ability to use gametes to create a sex binary. In these cases, other markers have to be reviewed for sex determination and none of these markers are binary.

Because binary means two separate and non-overlapping options, gamete production is not binary, it is trinary (sperm, egg, or none).

Second, biological sex is composed by a constellation of traits, so it would be medically inaccurate to isolate a single sex marker like gametes to determine an individual’s sex.

For the sake of science, let’s dig into greater detail below.

Gametes Are Not a Binary Variable

The reproductive organs have two primary components, the gonads (ovaries or testes) and the gametes they produce (eggs or sperm).

In aggregate, men do have testes and produce sperm, while women do have ovaries and produce eggs. However, intersex people exist who have both male and female gonadal tissue, sometimes called an ovotestis.

Additionally, intersex people can present with ambiguous gonadal tissue ranging from a underdeveloped (“hypoplastic”) to abnormal (“dysplastic”) gonads to streak gonads. Streak gonads are named after their unclear morphological shape.

Of course, testicular and ovarian cells can also be present at the same time, creating a gradation of cells that are both female and male. In people like this, there is “both testicular tissue with distinct seminiferous tubules and ovarian tissue containing mature graafian follicles in a single individual.”[1]

In many of these individuals, no gametes are produced. For example, no gametes are produced in 85% of individuals with streak gonads.[2]

Therefore, you cannot define the sex of these individuals by either their gonads or gametes.

To provide an example, people with Swyer syndrome have XY (“male”) chromosomes, but develop female reproductive organs, including a uterus and vagina. However, they lack ovaries. In place of ovaries, they develop streak gonads that are unable to produce gametes.[3] Therefore, these people have:

To review, the outcomes for gamete production are trinary not binary: sperm, eggs, or neither. Of course, the presence of no gametes is not a sex.

Rather, a lack of gametes creates a situation in which other markers must be assessed to determine sex, confirming sex is composed of a constellation of traits.

In these cases, other sex markers must be assessed, including but are not limited to: gonads, genitals, chromosomes, sex hormones, and secondary characteristics, such as breasts, body hair, and facial hair. No other sex marker is binary.

To summarize, people who have no gamete production coupled with duel or ambiguous gonads eliminate the ability to use gametes to create a sex binary. 

Gametes Aren’t Binary and Mix-and-Match with Other Traits

However, even that understanding would be incomplete, because newborns born with the common gamete types (eggs/sperm) can present with sex characteristics typical of the “opposite” sex. 

Specifically, gametes (egg or sperm) can mix-and-match with other sex markers—commonly, chromosomes, genitals, sex hormones, and secondary sex characteristics—to create a mosaic of sex traits.

Secondary sex characteristics include traits like body shape and size, facial hair, body hair, and voice.

For example, an intersex person could have a vagina and breasts, as well as undeveloped testes in their abdomen (“undescended”) that may or may not produce gametes. If you tried to “sex” this person, it would look like this:

This particular combination of sexual traits is common when androgen insensitivity (AIS) occurs.

An example of a person with this blend of traits is Castor Semenya, the renowned 800m runner. The Olympic Committee has not found a way to classify her sex because it varies across the biological sex markers, which is why they have defaulted to measuring her fluctuating androgen levels on a event by event basis.

Finally, testing a person’s gametes to determine biological sex is not used in a single country worldwide, making it poor criteria for sex determination from a functional perspective.

To summarize, we can’t create a sex binary using the reproductive organs (gametes and gonads), because:

Because neither gonads nor gametes are binary, biologists now understand sex to be determined by a constellation of traits. As mentioned above, none of these sex markers are binary in humans.

Requirements of Using Gametes for Sex Identification

If there are people who genuinely believe that we should use gametes to sex people, then they need to start petitioning for:

  1. The reclassification of the IDs of people with vaginas and breasts to “Male” (if there is an undescended testis with sperm production) and people with penises, scrotum, and facial hair to “Female” (if there is an internal ovary with egg production).
  2. The International Olympic Committee (IOC) to allow people to compete as “Female” based on their gametes, even if they have a penis, internal or external testes, or dramatically elevated levels of testosterone that provide a competitive advantage.
  3. Everyone to have their gametes checked at birth and puberty for sex determination.
  4. The U.S. or their local government to stop using external genitals at birth to issue IDs.
  5. The government to confirm the gamete type of every living adult.

Even then, however, we still lack a solution for how to sex people with ambiguous gonadal tissue and no gametes. In these cases, the only option is to revert to testing for other sex markers, confirming that sex is created by a constellation of traits.

To summarize, most people who believe in gamete sex binary don’t realize this decision requires some people with a penis to be assigned “female” and some people with a vagina to be “male”. I find this willingness surprisingly progressive!

As discussed, human sex cannot be isolated to a single trait like gametes. Rather, biological sex is composed of a mosaic of traits, of which there are several critical markers.

These biological markers of human sex include:

  1. Chromosomes – Types of chromosomal expression.
  2. Gonads – Organs that produce gametes.
  3. Hormones –Types and level of hormone secretion, which vary within and across the sexes.
  4. Secondary Sex Characteristics – Features that appear during puberty, but are not involved with reproduction.
  5. External Genitalia – Genitals visible outside the body.
  6. Internal Genitalia – Genitals present within the body.
  7. Gametes – Reproductive cells in humans.
  8. Gene Expression –Levels and types of gene expression. Genes dictate the proteins made by the body. Known genes that impact sex include DMRT1, SRY (produces Testis-Determining Factor), and Foxl 2.
  9. Brain Structure – Brain structure characteristics (including the ratio of white matter to grey matter) and brain activation patterns vary by sex.
  10. Hormone Receptor Sensitivity – The response to sex hormones depends on the activity of sex hormone receptors. Some individuals (like people with androgen insensitivity syndrome) are partially or completely insensitive to sex hormones, rendering them inert.

In summary, gametes cannot be used to create a sex binary in humans, because no gametes can be present along with ambiguous gonadal tissue. This third “undefined” possibility eliminates the possibility for a binary sex classification. Also, gametes are well known to mix-and-match with other sex traits—commonly, chromosomes, genitals, sex hormones, and secondary sex characteristics—making them one of multiple sex markers that in aggregate constitute a person’s sex as female, male, or a blend of both (intersex/undefined).

Were you taught that gametes created a sex binary when they do not? Ask your questions in comments below.
Interested to learn more? Join nearly two million other readers who are learning from Cade.

Footnotes

1. True hermaphroditism. True Hermaphroditism – An Overview | ScienceDirect Topics. Retrieved February 8, 2023, from https://www.sciencedirect.com/topics/medicine-and-dentistry/true-hermaphroditism. From: Avery’s Diseases of the Newborn (Eighth Edition), 2005.
2. Finlayson, C., Fritsch, M. K., Johnson, E. K., Rosoklija, I., Gosiengfiao, Y., Yerkes, E., Madonna, M. B., Woodruff, T. K., & Cheng, E. (2017). Presence of germ cells in disorders of sex development: Implications for fertility potential and preservation. Journal of Urology, 197 (3 Part 2), 937–943. https://doi.org/10.1016/j.juro.2016.08.108. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5309153/.
3. Fertilitypedia – Swyer Syndrome. Fertilitypedia. Retrieved February 7, 2023, from https://fertilitypedia.org/edu/diagnoses/swyer-syndrome.

*This article is part of a Biological Sex and Gender Diversity Series published by Cade Hildreth, B.A., M.S. You can read the other articles here:

AUTHOR BIO: Cade Hildreth attended Dartmouth College & Smith College for Undergraduate Studies in Biology and then acquired a Master’s Degree in Biochemistry and Molecular Biology with Specialization in Biotechnology & Bioinformatics from Georgetown University, where Cade was Valedictorian. Cade is the Founder/President of BioInformant.com, the world’s largest stem cell industry news site that attracts nearly one million views per year and serves all-star clients that include GE Healthcare, Pfizer, and Goldman Sachs. Cade has authored over one-thousand articles about the stem cells, interviewed hundreds of executives from across the industry, and presented at stem cell conferences worldwide. An expert on stem cells, Cade has been interviewed by the Wall Street Journal, Los Angeles Business Journal, Xconomy, and Vogue Magazine, as well as cited in Tony Robbin’s his best selling book, Life Force. 

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