The Yale Law Journal

February 2023

Sex Equality’s Irreconcilable Differences

Antidiscrimination LawGender and Sexual Orientation

abstract. This Feature uses recent developments in LGBTQ-equality law to unsettle sex equality’s enduring commitment to biology as a basis for sex discrimination. Sex equality rejects sex discrimination when it is based on sex stereotypes, defined as gross generalizations about women and men, but not when it is based on biological differences between the sexes, like pregnancy, anatomy, and strength. Biological justifications for race discrimination—once common—have been relegated to the trash heap of history. But biological justifications for sex discrimination persist. This is so because sex equality insists that biology alone is neither a stereotype nor an expression of bigotry. Biological rationales for sex discrimination remain attractive to lower federal and state courts, and have received the Supreme Court’s blessing, most recently in Dobbs v. Jackson Women’s Health Organization. The result is a broad swath of laws across substantive areas—including family law, tort, immigration law, criminal law, property, and abortion law—that sustain sex inequality courtesy of biology and despite a fairly robust anti-stereotyping principle.

This Feature argues that sex equality’s continued embrace of real differences should not survive what LGBTQ equality shows: that biologically rationalized sex discrimination is an illegal sex stereotype. It uses recent developments in LGBTQ equality surrounding sex, the body, procreation, and parenthood to unsettle sex equality’s beliefs in the reality of biological differences between the sexes and in the legality of laws based on those differences. It urges sex equality to grapple with what LGBTQ equality has to say about biology and its role in lawmaking and imagines what the American law of sex might look like when it does. Biologically rationalized sex distinctions have always been sex stereotypes. It is just that now, LGBTQ equality makes those stereotypes easier to see, harder to ignore, and impossible to justify.

author. Professor of Law, University of California, Irvine, School of Law. Many thanks to Avlana Eisenberg, Germaine Gurr, Douglas NeJaime, and Marc Spindelman for helping me think through many of the ideas expressed in this Feature and for generous comments on successive drafts. Thanks also to the faculties at the University of California, Irvine School of Law, the George Washington University Law School, and the University of Connecticut School of Law, where versions of this Feature were presented, and to the participants at Vanderbilt Law School’s Roundtable on LGBTQ Rights. The Yale Law Journal’s editorial team has made this Feature a much better product than when it first landed on their desks through their excellent suggestions and edits.


One legal doctrine tolerates criminal abortion laws on the ground that only women have abortions,1 but a kindred doctrine recognizes that men can get pregnant2—and, by implication, have abortions.

One legal doctrine tolerates sex discrimination in federal immigration law on the ground that children cannot be born of men,3 but a kindred doctrine rejects sexual-orientation discrimination in federal immigration law on the ground that children can be “born . . . of” men.4

One legal doctrine tolerates female-only criminal topless bans on the ground that women have physiologically distinct “female breasts,”5 but a kindred doctrine recognizes that trans men can be legal males without removing their “female breasts.”6

The first doctrine in each scenario above is sex equality’s doctrine of real differences. The second is the law of LGBTQ equality. It is this Feature’s objective to surface the tensions between the two in the hopes of building on sex equality’s existing strengths and of actualizing its untapped potential.

* * *

Last June, the Supreme Court relied on biology when it rejected the argument that a criminal abortion law rested on illegal sex stereotypes about women and mothers.7 Writing for the majority in Dobbs v. Jackson Women’s Health Organization, Justice Alito reasoned that abortion distinctions were not even sex classifications, let alone illegal sex discrimination or sex stereotyping, because abortion was unique to women.8 “The regulation of a medical procedure that only one sex can undergo does not trigger heightened constitutional scrutiny unless the regulation is a ‘mere pretex[t] designed to effect an invidious discrimination against members of one sex or the other,’” said
9 In other words, because only women had abortions,10 laws criminalizing abortion were nonsex classifications subject to (and constitutional under) rational-basis review11 rather than heightened scrutiny, the level of judicial review that sex classifications both warrant12 and need to smoke out illegal sex stereotypes.13 Dobbs said something that the Court has hinted at but never said explicitly: that laws based on characteristics unique to either sex are not sex classifications within the meaning of the Constitution.14 In so doing, the Court set the stage for biology to be an even greater roadblock than it already is to meaningful judicial review of sex discrimination.

Biology has always constrained what sex-discrimination jurisprudence—or sex equality—can, or is willing to, do.15 Sex equality’s crown jewel is the anti-stereotyping principle,16 which condemns laws reflective of gross generalizations about the way that women and men are.17 The anti-stereotyping principle has uprooted a lot of biologically rationalized sex discrimination, but it has never gone all the way: that is, it has never condemned all biologically rationalized sex discrimination. Rather, at some point, anti-stereotyping hits a wall of “real differences between the sexes” or “inherent biological differences between the sexes,” and it stops. Those inherent differences include pregnancy and birth,18 body parts (like breasts),19 strength and stature,20 violence,21 athletic ability,22 parental bonding,23 parental identification,24 and some parental responsibilities, both before and after a child is born.25 If a law treats women and men differently because of these differences, it is usually upheld on the ground that biology is real, as opposed to being a stereotype or a manifestation of bigotry.26 As one court recently put it: laws based on “physical differences between men and women” are not “stereotypes about men and women.”27 Biological justifications for race discrimination—once common28—are now universally condemned as expressions of racism and bigotry.29 By contrast, courts regularly tolerate biological justifications for sex discrimination as constitutionally innocuous expressions of fact. Even anti-stereotyping landmarks that reject biological rationales on anti-stereotyping grounds carve out space for some biologically rationalized sex distinctions to remain.30

This Feature argues that sex equality’s juggling act between anti-stereotyping and real differences should not survive what an allied doctrine increasingly shows: that biologically rationalized sex discrimination is a sex stereotype—all the way down. That allied doctrine is LGBTQ equality, defined as the statutory and constitutional law addressing the rights of people who depart from sex and gender norms. Using recent developments in LGBTQ equality surrounding sex, the body, procreation, and parenthood, this Feature unsettles sex equality’s beliefs in the reality of biological differences between the sexes and in the legality of laws based on those differences. It urges sex equality to grapple with what LGBTQ equality has to say about biology and its role in lawmaking and imagines what the American law of sex might look like when it does.

Anti-stereotyping and real differences have always been in conflict. For example, the anti-stereotyping principle prohibits laws that overgeneralize about men and
31 laws that treat men and women differently when they are, in fact, the
32 laws that prioritize groups over individuals;33 and laws that look backward rather than forward in time to determine whether sex discrimination is legal today.34 Biologically rationalized sex discrimination does all of the above, and yet, sex equality continues to insist that laws based on real differences are not sex stereotypes.35

Similarly, the anti-stereotyping principle prohibits laws that reflect and reproduce social judgments about men and women, but biologically rationalized sex discrimination allows social judgments about men and women to flourish in plain sight.36 For example, the Supreme Court has condoned laws that assume that fathers have less robust connections to their children at birth than mothers—a social judgment—by casting those laws as neutral expressions of a biological fact, namely, the fact that no man can give birth.37

Likewise, the anti-stereotyping principle condemns laws that create “self-fulfilling prophecies”38 about men and women, but laws rooted in real differences create self-fulfilling prophecies about men and women. For example, real differences helps explain why federal employment law provides leave protection to expectant mothers but not to expectant fathers to attend parenting classes and prenatal appointments.39 However, leave protection for mothers but not fathers to engage in caretaking before pregnancy leads to “[s]ticky behaviors marking women as caregivers and men as providers” well after pregnancy is over, as David Fontana and Naomi Schoenbaum argue.40 Similarly, real differences is one of the reasons for female-only criminal topless bans,41 but female-only criminal topless bans make us see women’s bodies—and women generally—as inherently sexual.42 In both of those examples, it is the logic of real differences that ends up creating the very differences that the anti-stereotyping principle ought to reach.43

While always in tension with sex equality’s anti-stereotyping principle, real differences is increasingly in tension with LGBTQ equality. For years, real differences stymied LGBTQ equality. Transgender people could be denied marital, parental, and employment rights because their biology did not fit their gender identity.44 Individuals could not change their legal sex on official documents like birth certificates because sex was immutable.45 Same-sex couples could not legally engage in consensual sex nor marry because they could not procreate with each other.46

Increasingly, however—and in some contexts, overwhelmingly—LGBTQ equality is unsettling real differences. It is doing so in two ways. First, LGBTQ equality is upending the reality of real differences by recognizing phenomena—like pregnancies in men,47 children being “born . . . of” two women or two men,48 and nonbinary sex designations49—that real-differences arguments overlook. Second, LGBTQ equality is unsettling the legality of real differences by rejecting biological justifications for LGBTQ discrimination, often on sex-stereotyping grounds that carry forward the anti-stereotyping principle to new terrain: discrimination based on “biology alone.”50 For example, defenders of transgender bathroom bans have argued that the bans are not sex stereotypes because they discriminate because of “physiology, period,”51 and because the Supreme Court has held that discrimination for purely physiological reasons is beyond the reach of the anti-stereotyping principle.52 In response, courts have held that discrimination due to “physiology, period” violates sex equality because it overgeneralizes about male and female anatomy and fails to treat individuals as individuals, with both effects prohibited by the anti-stereotyping principle.53 As one court put it, anti-stereotyping protections reach “the entire spectrum of disparate treatment of men and women resulting from sex stereotypes,”54 whether the stereotypes are gross generalizations about social roles or gross generalizations about the body.

This Feature argues that these developments in LGBTQ equality matter for sex equality because sex equality and LGBTQ equality matter for each other. They came of age together in the 1960s and 1970s, when second-wave feminists and gay liberationists “revolt[ed] against the [same] sex-role structure,”55 at times “join[ing] together and publicly affirm[ing] their shared commitment to eradicating sex-role stereotyping.”56 They deal with statuses (sex, sexual orientation, and gender identity) and forms of discrimination (sex, sexual-orientation, and gender-identity discrimination) that interrelate, as the Supreme Court recognized when it held in Bostock v. Clayton County that sexual-orientation and transgender discrimination is illegal sex discrimination under federal employment law.57 They overlap doctrinally, especially since Bostock prompted dozens of lower and state courts to find that LGBTQ discrimination is illegal because it is sex discrimination.58

This Feature asks: Given the historical, conceptual, and doctrinal connections between sex equality and LGBTQ equality, how can sex equality credit the law and logic of real differences when LGBTQ equality disrupts the law and logic of real differences? If sex equality and LGBTQ equality are fundamentally about sex, then how can sex equality condone biological justifications for sex discrimination as something other than sex stereotypes when LGBTQ equality shows that biological justifications for LGBTQ discrimination are sex stereotypes? If sex equality and LGBTQ equality are of a piece, then how can sex equality conceptualize biology and biologically rationalized sex discrimination in one way and LGBTQ equality conceptualize biology and biologically rationalized LGBTQ discrimination in a different way?

Consider the Introduction’s third scenario, which juxtaposed sex equality’s approach to issues of body regulation and LGBTQ equality’s approach to issues of body regulation. Every state and thousands of localities have laws and regulations that penalize females, often as young as ten,59 for being topless in every space imaginable, including on beaches,60 in adult entertainment clubs,61 in the water,62 in forests,63 and at home.64 In 2017, the Seventh Circuit upheld Chicago’s topless law as a valid expression of real differences between male breasts and female breasts,65 relying, in part, on the Supreme Court’s recognition in United States v. Virginia that “[p]hysical differences between men and women . . . are enduring.”66 In so doing, the Seventh Circuit joined dozens of state and federal courts that have upheld female-only topless bans over the past fifty years by reasoning that women’s breasts are socially different because they are physically different,67 either because of “the size of the [female] breast”68 or because the female breast, unlike the male breast, is “a mammary gland”69 that (somehow) serves a “procreative function.”70 Even the exceedingly few courts that have struck down topless laws on stereotyping grounds acknowledge that male and female breasts are physically different and that laws based purely on biological difference are constitutional. For these courts, criminal topless laws are not grounded in real differences, but if they were, they would pass constitutional muster.71

The same year that the Seventh Circuit ruled that Chicago’s topless regulation was a valid expression of real differences, Illinois passed a law eliminating the requirement that people change their bodies—including their breasts—to change their legal sex.72 Since then, more states have joined Illinois in eliminating surgical requirements for legal-sex changes to official documents like birth certificates.73 In some cases, courts have enjoined enforcement of surgical requirements that remain on the books by strongly suggesting that they constitute illegal sex stereotyping under the Equal Protection Clause.74 One court, for instance, recently ruled that Alabama’s surgical requirements for driver’s license changes likely violated the Constitution’s prohibition of sex discrimination because those requirements imposed the State’s understanding of sex on private individuals, “denying [those individuals] the ability to decide their sex for themselves instead of being told who they [we]re by the State.”75 The court noted that anti-stereotyping landmarks like United States v. Virginia and Sessions v. Morales-Santana prohibited laws that “‘rely on overbroad generalizations’ about the roles and attributes of men and women,” and reasoned that surgical requirements fell into that category because they overgeneralized about male bodies and female bodies.76 In so doing, the court rejected the State’s bid to view the surgical requirements as simple expressions of real biological differences between the sexes, which, the State urged, were constitutionally valid under existing Supreme Court jurisprudence.77

LGBTQ equality disrupts states’ arguments that topless bans are constitutional reflections of physical differences between the sexes—arguments that courts credit.78 First, sex-change jurisprudence (an LGBTQ-equality issue) establishes that people do not have to lose breasts or get breasts to change their legal sex. As such, how can topless jurisprudence (a sex-equality issue) assure that breasts always track legal sex? Of course, breasts have never invariably tracked legal sex: many men have “female-looking” breasts, and many women have “male-looking” breasts. But to the extent that LGBTQ equality now recognizes as a matter of law that breasts and sex do not invariably align, how can sex equality insist that they do? Does LGBTQ equality not make an already gross generalization about male and female anatomy grosser?79 And in doing that, does it not help us see what we already know: that criminal topless bans are policing not breasts but women,80 which, according to the philosopher Kate Manne, is the very definition of misogyny?81

Second, legal-sex-change jurisprudence suggests that it is a sex stereotype for the state to craft legal rules with coercive effects around the state’s understanding of the relationship between sex and bodies. If that is right, then why isn’t it a sex stereotype for the state to enact topless bans with coercive effects that codify the state’s understanding of male and female breasts? The analogy might not be perfect, but it is close enough for us to wonder why sex equality tolerates actions that LGBTQ equality condemns on anti-stereotyping grounds.

The point is that when we juxtapose sex equality and LGBTQ equality in this way—which the dialogic and intersectional relationship between sex equality and LGBTQ equality would seem to require—then it becomes easier to see and harder to ignore the problems with all real-differences justifications for sex discrimination. Radical feminists and queer theorists have long argued that biological justifications for sex difference and sex discrimination are sex stereotypes because culture always shapes our understanding of biological categories.82 As Katherine M. Franke wrote more than two decades ago, “By accepting these biological differences, equality jurisprudence reifies as foundational fact that which is really an effect of normative gender ideology.”83 Agreeing with Franke’s argument, this Feature uses recent developments in the law of LGBTQ equality to make those stereotypes more visible and less defensible.

The remainder of this Feature unfolds in four Parts. Part I describes the two faces of contemporary sex equality—real differences and anti-stereotyping—and identifies the tensions between them. Part II summarizes the relationship between biology and LGBTQ equality both historically and today. It shows that historically, biological arguments constrained LGBTQ equality, whereas today, LGBTQ equality is constraining biological arguments, often by conceptualizing biologically rationalized LGBTQ discrimination as a sex stereotype. Part III argues that sex equality’s continued allegiance to real differences cannot be reconciled with what LGBTQ equality reveals about biology and about biologically rationalized sex discrimination. Part IV imagines what the law might look like if it were more responsive to LGBTQ equality’s understanding of biology and addresses fears that readers might have about eliminating real differences from the American law of sex.