Is Sex Binary if Sexual Reproduction Is Binary?

A Pro/Con Dialogue
Sex & Gender
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pro
con

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pro
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The sexes are defined by their roles in reproduction. Males make sperm. Females make eggs. There are no other sex cells, so there are no other sexes.

con

Sex depends on more than sex cells. There are sex organs and hormones and chromosomes. Combined or apart, these are not all strictly binary. Just look at the variety of intersex traits.

pro

Reproductive organs matter, particularly the gonads, as do the mechanisms that make them male or female. When those mechanisms misfire, intersex traits are the result, but intersex individuals are not a distinct sex. They’re people with very rare conditions who are almost always sterile. The few who can reproduce make sperm or ova.

con

Intersex people blur the line between the sexes. Sex anatomy can be ambiguous or mismatch with a person’s sex chromosomes, and sex chromosomes can be other than just XX and XY, not to mention differ from cell to cell. So-called male and female hormones don’t sharply divide the sexes either. Typical human bodies have both testosterone and estrogen.

pro

Average hormone levels differ by sex, especially once puberty starts and especially for testosterone. Plus, testosterone masculinizes the body and estrogen feminizes it. Hormones aside, you’re talking about disorders of sex development. Some affect how sex is determined, but none change how it’s defined. Sexual reproduction, a fundamentally binary, sperm-egg process, is the objective biological basis for the two sexes.

con

Sex is assigned to bodies, and intersex bodies defy the male-female binary. Yet most states mark them all M or F at birth. Some intersex infants undergo life-altering surgeries to normalize—potentially remove or desensitize—their genitalia, all to approximate a sex they may later reject. For intersex people, binary sex is not a biological fact. It is a legal and medical fiction with real social and psychological consequences.

pro

Intersex conditions are hard cases, but saying they show human sex isn’t binary is like saying congenital leg amputations show humans don’t walk on two legs. It’s like saying a coin doesn’t have two sides because .02% of tosses land on the coin’s edge. The other 99.98% come up heads or tails, and the same percent of humans are born clearly male or female.

con

The three Gs—genetics, gonads, and genitalia—are generally dimorphic. Even so, sex organs differ by degree, not kind, since they form from the same embryonic tissue. Other bodily, including hormonal, sex differences are also a matter of degree and show substantial group overlap and individual variation. Little to no dimorphism is found in human brains and behavior. Overall, human sex isn’t binary. Viewed in all its complexity, human sex is a spectrum.

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Notes

  1. An organism’s sex is defined by the type of gamete (sperm or ova) it has the function of producing. Males have the function of producing sperm, or small gametes; females, ova, or large ones1 … [H]owever…sex of individuals within a species isn’t based on whether an individual can actually produce certain gametes … [A]n individual’s biological sex corresponds to one of two distinct types of evolved reproductive anatomy (i.e. ovaries or testes)2

    1 A Biologist Explains Why Sex Is Binary, 2 Sex Is Not a Spectrum

    Some states have proposed laws defining sex as either male or female based on gamete production. For example, see: Kansas’ rights bill angers left with its definition of ‘woman’.

  2. No third type of sex cell exists in humans, and therefore there is no sex “spectrum” or additional sexes beyond male and female. Sex is binary.

    The Dangerous Denial of Sex

    Because no other types of gametes exist in animals or vascular plants, and we see no intermediate gametes, there is no third sex.

    The Ideological Subversion of Biology

    Also see In Humans, Sex is binary and immutable.

  3. The production of gametes does not sufficiently describe sex biology in animals, nor is it the definition of a woman or a man … The bottom line is that while animal gametes can be described as binary (of two distinct kinds), the physiological systems, behaviors and individuals that produce them are not.

    Here’s Why Human Sex Is Not Binary

    In the 1950s the psychologist John Money and his colleagues studied people born with unusual combinations of sex markers (ovaries and a penis, testes and a vagina, two X chromosomes and a scrotum, and more). Thinking about these people, whom today we would call intersex, Dr. Money developed a multilayered model of sexual development.

    Why Sex Is Not Binary

    Money’s model identifies five biological layers or levels:

    1. Chromosomal (XX, XY, XXY …)
    2. Fetal gonadal (ovaries, testes)
    3. Fetal hormonal (estrogen, testosterone)
    4. Internal reproductive (fallopian tubes, vas deferens, …)
    5. External genital (vagina, clitoris, penis, scrotum)

  4. Science keeps showing us that sex…doesn’t fit in a binary, whether it be determined by genitals, chromosomes, hormones, or bones (which are the subject of my research).

    We Finally Understand That Gender Isn’t Binary. Sex Isn’t, Either

    [E]ach…layer [of sexual development, from chromosomal to genital] does not always become strictly binary.

    Anne Fausto-Sterling. Why Sex Is Not Binary

  5. Intersex is an umbrella term for differences in sex traits or reproductive anatomy. Intersex people are born with these differences or develop them in childhood. There are many possible differences in genitalia, hormones, internal anatomy, or chromosomes, compared to the usual two ways that human bodies develop.

    FAQ – What is intersex?

    InterACT, an advocacy organization supporting the human rights of children born with intersex trait, identifies nearly 50 intersex variations.

  6. [A]n individual’s sex is defined by the type of gamete (sperm or ova) their primary reproductive organs (i.e., gonads) are organized, through development, to produce.

    Colin Wright. Understanding the Sex Binary

  7. [H]uman hermaphrodites (vanishingly rare, and almost invariably sterile) or individuals with disorders of sex development (DSDs) are not members of distinct sexes…

    Jerry Coyne. Agustín Fuentes grossly misrepresents the sex binary…

    Anne Fausto-Sterling…claimed in the 1990s that…there were…at least five sex categories, and perhaps even more. However, the additional sexes she proposed simply corresponded to various intersex conditions, not new sexes akin to the functional reproductive roles of producing either sperm or ova…

    Colin Wright. Are There More Than Two Sexes? No.

  8. For example, see:

  9. A DSD [disorder of sex development] called congenital adrenal hyperplasia (CAH), for example, causes the body to produce excessive amounts of male sex hormones; XX individuals with this condition are born with ambiguous genitalia (an enlarged clitoris and fused labia that resemble a scrotum).

    Sex Redefined: The Idea of 2 Sexes Is Overly Simplistic

    Also see Ambiguous Genitalia and Disorders of Sexual Differentiation. Note the article says that intersex is not current medical terminology. Disorder of sex development (DSD) is.

  10. Disorders of sex development (DSD) are rare disorders occurring when there is a discordance between chromosomal, gonadal, or phenotypic [e.g. genital] sex.

    Genetic Diagnosis of Endocrine Disorders (2nd ed.) – Chapter 19 – Disorders of Sex Development.

    An XX baby can be born with a penis, an XY person may have a vagina, and so on. These kinds of inconsistencies throw a monkey wrench into any plan to assign sex as male or female, categorically and in perpetuity, just by looking at a newborn’s private parts.

    Anne Fausto-Sterling. Why Sex Is Not Binary

    Complete androgen insensitivity syndrome, or CAIS, for example, arises when a person’s cells are deaf to male sex hormones … People with CAIS have Y chromosomes and internal testes, but their external genitalia are female, and they develop as females at puberty.

    Claire Ainsworth. Sex Redefined: The Idea of 2 Sexes Is Overly Simplistic

  11. [A]n egg or sperm may lack a sex chromosome or have an extra one. The resultant embryo has an uncommon chromosomal sex — say, XXY, XYY or XO. So…there are more than two categories.

    Anne Fausto-Sterling. Why Sex Is Not Binary

    Along with XX and XY, there are 9 other viable variations. Chromosome mosaicism is when different variations occur in different cells in the same body.

  12. The common assumption that every cell contains the same set of genes is untrue. Some people have mosaicism: they develop from a single fertilized egg but become a patchwork of cells with different genetic make-ups.

    Claire Ainsworth. Sex Redefined: The Idea of 2 Sexes Is Overly Simplistic

    For example, see: The Woman Who Gave Birth Despite Most Of Her Cells Having XY Chromosomes. Yale Medicine has more on chromosome mosaicism.

  13. Our hormones are the same. They function the same ways and we all have the same hormones … there are no “male” or “female” hormones.

    Agustin Fuentes. Men and Women Are the Same Species!

    [T]hese hormones, as well as progesterone, are produced by both ovaries and testes as well as the adrenal glands and through peripheral conversion in fatty tissue; these sources are present in all bodies.

    Janet Shibley Hyde, et al. The Future of Sex and Gender in Psychology: Five Challenges to the Gender Binary

    Also see Stop Using Phony Science to Justify Transphobia, particularly the section The Body and the Brain and the Hormones Betwixt.

  14. In the healthy, normal males and females, there was a clear bimodal distribution of testosterone levels, with the lower end of the male range being four- to fivefold higher than the upper end of the female range…

    Richard Clark, et al. Large Divergence in Testosterone Concentrations Between Men and Women: Frame of Reference for Elite Athletes in Sex-Specific Competition in Sports, a Narrative Review

    [F]rom puberty onward a clear sex difference…emerges as circulating testosterone concentrations rise in men because testes produce 30 times more testosterone than before puberty with circulating testosterone exceeding 15-fold that of women at any age.

    David Handelsman, et al. Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance

  15. [A]ndrogens [including testosterone] are the key elements for the differentiation of male internal and external genitalia as well as other sexual organs and general body composition…

    The Differential Role of Androgens in Early Human Sex Development

    Testosterone plays a key role in male sex development in utero as well as during puberty. The masculinizing effects of testosterone are the basis for masculinizing hormone therapy, which aims to induce development of male secondary sex characteristics, and suppression/minimization of female secondary sex characteristics, says the Gender Affirming Health Program at University of California, San Francisco.

  16. The feminizing effects of estrogen are the basis for feminizing hormone therapy, which aims to induce development of female secondary sex characteristics, and suppression/minimization of male secondary sex characteristics, says the Gender Affirming Health Program at University of California, San Francisco.

  17. [T]he notion that XX males and females with a Y chromosome debunk the claim that sex is determined by chromosomes…conflates how sex is determined with how sex is defined for an individual … [T]hough an individual’s sex is mechanistically determined in different ways, it is always defined the same way—by the type of gamete his or her primary reproductive organs is organized around producing. This should be obvious, as it would have been impossible ever to have discovered these different sex-determining mechanisms without first knowing what males and females are apart from sex chromosomes…

    Colin Wright. Understanding the Sex Binary

  18. Assigned sex is a label that you’re given at birth based on medical factors, including your hormones, chromosomes, and genitals … Some people call the sex we’re assigned at birth biological sex. But this term doesn’t fully capture the complex biological, anatomical, and chromosomal variations that can occur. Having only two options (biological male or biological female) might not describe what’s going on inside a person’s body.

    Sex and Gender Identity

    For critical discussion of sex assigned at birth in the context of transgender rights, see Sex Assigned at Birth in the Columbia Law Review.

  19. Few legal systems allow for any ambiguity in biological sex, and a person’s legal rights and social status can be heavily influenced by whether their birth certificate says male or female.

    Claire Ainsworth. Sex Redefined: The Idea of 2 Sexes Is Overly Simplistic

    Only 16 states plus D.C. offer non-binary birth certificates.

  20. Infant intersex surgeries often come with serious lifelong emotional and physical consequences, high complication rates, and reduced sexual function … Some kids may grow up and want to change their bodies, or be glad that their bodies were changed. Many other kids and adults live with incredible pain and trauma because these choices were made for them.

    InterACT. FAQ – What is intersex surgery?

    Also see: ‘You can’t undo surgery’: More parents of intersex babies are rejecting operations.

  21. [S]urgery to ‘normalize’ their genitals … is controversial because it is usually performed on babies, who are too young to consent, and risks assigning a sex at odds with the child’s ultimate gender identity—their sense of their own gender.

    Claire Ainsworth. Sex Redefined: The Idea of 2 Sexes Is Overly Simplistic

  22. See, for example, Male or female? Babies born on the sliding sex scale, which draws from the BBC One documentary Me, My Sex and I.

  23. While it may be necessary to outline reasonable policies and laws for hard cases [i.e. intersex conditions], we need not pretend we’re all hard cases.

    Colin Wright. Understanding the Sex Binary

  24. The fact that some humans are intersex in no way diminishes the truth of sexual dimorphism, any more than the fact that some humans are born missing lower limbs diminishes the truth of the statement that humans are bipedal.

    Sex and Gender: A Beginner’s Guide

  25. By way of analogy: We flip a coin … [A] coin also has an edge, and about one in 6,000 (0.0166 percent) throws (with a nickel) will land on it. This is roughly the same likelihood of being born with an intersex condition. Almost every coin flip will be either heads or tails, and those heads and tails do not come in degrees or mixtures. [internal links omitted]

    Colin Wright. Sex Is Not a Spectrum

    [T]he calculated chance of a tossed nickel landing on its side is almost the same as the chance of a human being born as an intersex, supposedly violating the sex binary by being neither male nor female. Yet we don’t, when tossing coins, say, Call it: heads, tails, or edge. If you’re going to insist that there be NO production of humans that are neither male nor female—even in a trillion individuals—before you accept a binary, you are being obtuse—and denying the reality of how nature really works.

    Jerry Coyne. Coin-Tossing and the Sex Binary

  26. In humans, and transgender and so-called non-binary people are no exception, this reproductive anatomy is unambiguously male or female over 99.98 percent of the time … Just because sex may be ambiguous for some does not mean it’s ambiguous (and, as some commentators would extrapolate, arbitrary) for all. [internal links omitted]

    Colin Wright. Sex Is Not a Spectrum

    Some critics of the binary model of human sex estimate that 1% to 2% of individuals are born intersex. For example, see: The Future of Sex and Gender in Psychology: Five Challenges to the Gender Binary.

  27. If one considers a binary to mean that two distributions are largely non-overlapping and internally homogenous, then there is a relative binary human sex system in a limited set of characteristics referred to by some as the genetics-gonad-genitalia triad (i.e., 3G sex). These 3G characteristics are tightly correlated with one another and have high internal reliability within-individuals. [internal citations omitted]

    Challenging the Binary: Gender/Sex and the Bio‐Logics of Normalcy

  28. Two fundamental assumptions underlie current thinking about sex as a biological system and about its relations with other systems: (a) that sex is a dimorphic system (i.e., a system that can take one of only two forms), and (b) that the effects of sex on other systems (e.g., the brain, gender identity) are characterized by a dimorphic outcome (e.g., male vs. female brain, male vs. female gender identity).

    Janet Shibley Hyde, et al. The Future of Sex and Gender in Psychology: Five Challenges to the Gender Binary

    The gonads and internal genitals are each generally dimorphic, according to the authors.

  29. [T]he reproductive organs and external genitalia [of males and females] do differ in certain ways. However, these differences are more of degree than kind, since the same embryonic tissue mass gives rise to both female and male genitalia.

    Agustin Fuentes. Race, Monogamy, and Other Lies They Told You: Busting Myths About Human Nature

  30. A newly fertilized embryo initially develops without any indication of its sex. At around five weeks, a group of cells clump together to form the bipotential primordium. These cells are neither male nor female but have the potential to turn into testes, ovaries or neither … SRY [a gene on the Y chromosome] plays a role in pushing the primordium toward male gonads … [G]enes like DMRT1 and FOXL2 maintain certain sexual characteristics during adulthood. If these genes stop functioning, gonads can change and exhibit characteristics of the opposite sex. [internal links omitted]

    Stop Using Phony Science to Justify Transphobia

  31. [I]ndividuals more or less conform to a general division based on which genitals one has (which is not a definition of biological sex), but with a range of variation in things like hormone levels and function, physical developmental patterns, hair growth, and other physiological processes.

    Agustin Fuentes. Busting Myths About Sex and Gender

  32. [A]lthough testosterone levels are higher in men than women, on average, the difference is much smaller than widely believed and the distributions show considerable overlap. [internal citations omitted]

    Janet Shibley Hyde, et al. The Future of Sex and Gender in Psychology: Five Challenges to the Gender Binary

    Following puberty, on average females have higher estrogens until menopause when compared to males. But this blunt characterization of averages masks variation within and similarity between these two groups.

    L. Zachary DuBois, Heather Shattuck-Heidorn. Challenging the Binary: Gender/Sex and the Bio‐Logics of Normalcy

  33. [M]easurements of sex hormones levels in any one individual wildly vary across the range of average values regardless of how close or spread apart you take the measurements. [internal links omitted]

    Simon(e) Sun. Stop Using Phony Science to Justify Transphobia

  34. It is a common assumption that parts of the male and female brain have evolved to focus on different things: that men seek sex, competition, and status, and women seek protection and security, to be social and caretaking … [T]here has been an intensive search for measurable biological differences in men’s and women’s brains. The results…are negligible…

    Agustin Fuentes. Busting Myths About Sex and Gender

    Although many studies have reported differences between women and men in brain structure, these differences are not sexually dimorphic; rather, there is considerable overlap between the distributions of women and men … [M]ost brains are gender/sex mosaics.

    Janet Shibley Hyde, et al. The Future of Sex and Gender in Psychology: Five Challenges to the Gender Binary

    By gender/sex mosaic, Hyde et al. mean having at least one element with the female-end form and at least one element with the male-end form. For example, even though part of the hypothalamus is, on average, two times bigger in men than in women, its size falls in the female range in about 30% of men, according to the authors.

  35. The assumption of…prevalent gender stereotypes is that males and females are vastly different in their personality, abilities, interests, attitudes, and behavioral tendencies. This assumption is referred to as the gender differences hypothesis … We utilized data from over 20,000 individual studies and over 12 million participants … [A]cross most topic areas in psychological science, the difference between males and females is small or very small.

    Ethan Zell, et al. Evaluating Gender Similarities and Differences Using Metasynthesis (Hat Tip Race, Monogamy, and Other Lies They Told You)

  36. [B]iological sex is not best envisioned as a binary (XX versus XY) but rather as a broad spectrum of developmental patterns and processes. To varying extents, many of us are biological hybrids on a male-female continuum.

    Agustin Fuentes. Busting Myths About Sex and Gender

    For a visualization of the proposed sex spectrum, see this graphic from Scientific American.

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