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 ones.

    A Biologist Explains Why Sex Is Binary

    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.

    Here’s Why Human Sex Is Not Binary

    Biologist Anne Fausto-Sterling endorses a multilayered model of sexual development. Developed in the 1950s by psychologist John Money, who studied intersex individuals, this 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)
    Anne Fausto-Sterling. Why Sex Is Not Binary

  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.

    FAQ – What is intersex?

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

  6. [S]ex 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).

    Colin Wright. Sex Is Not a Spectrum

  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…

    Also see Colin Wright on Anne Fausto-Sterling’s past claim that there are at least five sex categories, and perhaps even more.

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

  8. For example, see:

  9. For example, XX individuals with congenital adrenal hyperplasia (CAH) have a clitoris and labia, but the former is enlarged and the latter are fused and scrotum-like. Source:

    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.

    Anne Fausto-Sterling. Why Sex Is Not Binary

    For example, in complete androgen insensitivity syndrome (CAIS), Y chromosomes, internal testes, external female genitalia, and female puberty are all present. Source:

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

  11. Along with XX and XY, there are 9 other viable variations. Given these variations, Fausto-Sterling concludes there are more than two categories of sex from the very start of development.

    Anne Fausto-Sterling. Why Sex Is Not Binary

  12. 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. Once puberty starts, men have 15-times more circulating testosterone than women. Source:

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

    Also see:

    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

  15. 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.

    Also see:

    The Differential Role of Androgens in Early Human Sex Development

  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]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.

    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 … [h]aving 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…

    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.

    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

    See also:

    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. [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). [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. [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

    Also see DuBois and Shattuck-Heidorn on averages as a blunt and incomplete characterization of hormonal sex differences.

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

  33. According to Simon(e) Sun, individual hormone levels vary wildly across an average or sex-typical range, even when measured close together in time.

    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 … [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 … [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 … [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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