Last week, the president of the American Anthropological Association weighed in on one of the most polarizing subjects in her field: biological sex. Some anthropologists believe that biological sex is binary, and that it is a necessary and useful category; others believe that this position is at odds with settled science and is a threat to people’s “safety and dignity,” as the AAA put it in an official statement. In 2023, organizers of a large anthropology conference canceled a panel that sought to defend the importance of biological sex to the field.Anthropology scholars, in particular, should be unusually adept at accurately reconstructing human beliefs that they do not share. But the AAA’s president, Carolyn M. Rouse, says that she’s baffled by the whole debate.Rouse, who is also a tenured professor at Princeton, addressed the question during a lengthy interview with The Chronicle of Higher Education. “The idea that there are two sexes is just factually incorrect,” she stated, arguing that “all you need to do is literally type into Google” to see that we know “there are different types of ‘sexes’ and ‘genders.’” In a curious aside, she added, “You may not like it. I don’t know, maybe you want to kill babies that aren’t just XX presenting XX or XY presenting XY, but that’s what we have in this world.” In Rouse’s telling, scholars who believe that biological sex is a useful analytic category are not only wrong but engaging in “nonsensical” speech that is no more fit for consideration in their field than astrology is fit for astronomers. “I still don’t know what people mean” when they assert that sex is binary, she said, or “why that matters to people so much.” She called the belief “very strange.”Rouse’s comments reveal that she does not even understand the position that she is dismissing. Anthropology is the study of humanity, and scholars in the field are charged with understanding our species, past and present, in all of its diversity. Their ambit includes our belief systems. And a belief in two sexes is one of the most common in human history. That a belief is common does not make it correct, but it is jarring for a leader representing anthropologists to talk about a position held by billions of humans in wildly different times and places as if it is both “very strange” and beyond comprehension.Scholars are well within their rights to reject the notion that sex is binary—many anthropologists share this view, including Princeton’s Agustín Fuentes, who explains his logic in Sex Is a Spectrum. But instead of a fair-minded appraisal of the matter, Rouse showed conspicuous incuriosity about other scholars’ work. It is striking how little she seems to know about the particular reasons that many fellow scholars believe that biological sex is binary. Just as striking is how she responds to not knowing. She could apply her scholarly tool kit to understand what others think and why. Instead, she treated their view as unworthy of debate and said that academics might be right to keep it out of conferences. She doesn’t “know what people mean”––yet she is certain that their wrongness is settled.Her interviewer, Stephanie M. Lee, reacted by pointing out that in 2022, in a survey of forensic anthropologists, 42.4 percent of respondents expressed the belief that sex is binary, implying that the question simply isn’t settled in the field. Lee said, “I was wondering how you explain that.” Rouse responded, “I don’t believe in opinion research,” then added, “Not to disparage them, but a lot of forensic people, they’re coroners, they’re doing it in a practicing level, where they’re actually asked on forms to determine whether this body is male or female, oftentimes they haven’t had advanced schooling.” In fact, the journal Forensic Anthropology published data on the respondents: 57.9 percent had a doctorate, and another 25.7 percent had received a master’s degree; the most common degree concentrations among respondents were forensic anthropology and biological or physical anthropology. Just 20.5 percent worked in a coroner’s office. And flimsy claims aside, these attacks on survey respondents’ credentials evaded the substance of the matter.All of this seems contrary to the spirit of anthropology. If the goal of the field is to understand humans, what kind of scholar professes ignorance of a common viewpoint and why its adherents value it, and rejects surveys, panels, and debates that clarify what others believe?Granted, like many coroners, I lack advanced education in anthropology. But even journalism can add clarity here. Rouse stated, “Binary means two. So, what are the two? One is XX and one is XY, but we know that there are more than that. That’s not binary.” She alluded to the fact that although most humans have either XX or XY chromosomes, there are some cases in which a person’s chromosomes are XXY, XYY, or XXX, and rare cases in which they are XXYY, XXXY, et cetera. If a scholar were to define every variation as a different sex, then sex would not be binary.But scholars who believe that sex is binary do not define sex based on chromosomes alone. Typically, their position goes something like: Human reproduction is organized around two types of gametes and two corresponding reproductive roles: small gametes, or sperm, produced by males and large gametes, or ova, produced by females. In this important sense, sex is binary. There is no third type of gamete, just the male and female gamete.Carole Hooven, an evolutionary biologist with a Ph.D. in biological anthropology, had been slated to appear on the American Anthropological Association panel that got cancelled. She is a proponent of the “gametic view.” Far from denying the complexity of life, her account of binary sex acknowledges it. In her telling, its usefulness is due in part to the fact that “it applies across sexually reproducing animals and accommodates all the complexity and variation within the sexes. It holds in nonreproductively viable animals—like postmenopausal me—that don’t produce gametes,” she writes; “it holds in male seahorses that get pregnant; in clownfish who change from male to female (first producing sperm and then eggs); in females who identify as male (trans men) and take male levels of testosterone and have a deep voice and a thick, bushy beard.” As for how it maps onto humans in particular, she writes, “Traits associated with sex—like chromosomes, hormones, brain, feelings, or behavior—are not binary; nor do they define sex. However, there are two, and only two, sexes.”After understanding the gametic view, one can explore any number of challenges to it––a proponent of it, Colin M. Wright, who holds a Ph.D. in evolution, ecology, and marine biology from UC Santa Barbara, summarizes many of them in his article “Why There Are Exactly Two Sexes.” For example, some people argue that sex is not binary, because some people are intersex. “A person might be born appearing to be female on the outside, but having mostly male-typical anatomy on the inside. Or a person may be born with genitals that seem to be in-between the usual male and female types,” the Intersex Society of America explains. “Or a person may be born with mosaic genetics, so that some of her cells have XX chromosomes and some of them have XY.” (This last point resembles one of the arguments that Rouse employed in her recent interview as if it was a decisive rejoinder to the notion of two sexes.)Wright’s response to that line of argument is that “the sex binary does not entail that every individual can be unambiguously categorized as male or female.” The claim is that “there are only two gamete types, sperm and ova, and thus only two sexes. Sexual ambiguity is not a third or intermediate sex because developmental variation does not correspond to producing new gamete types.”Both Wright’s position and the counterarguments are easy to understand, whatever view one holds. Neither side is “nonsensical.” And the point is not to pick a side. It is, rather, that the AAA and its president have an obligation to understand all relevant positions and convey them accurately––and to eschew ad hominem rhetoric such as denigrating coroners and speculating that people who think sex is binary may want to kill babies.In popular discourse, one can doubtless find many weak and flawed arguments for why sex is binary. What hope does anthropology have for understanding those beliefs––which its scholars should try to do, given their overall mission of understanding people––if the field can’t even give a fair shake to scholars with the steelman version? These academics have presented a coherent, internally consistent, scientifically grounded case for sex as binary that many scholars share.Anthropologists would do their discipline’s reputation some good if they collectively signaled that they have no confidence in leaders who behave this way. To understand humans, anthropologists must be able to understand the humans with whom they disagree.