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Sex on the Spectrum

Is there a left-wing form of evolution denialism?
February 16, 2019 | Comments

We wrote recently about evolution denialism, a phenomenon usually attributed to people who hold right-wing and/or fundamentalist religious beliefs.  We were thus quite struck when an article appeared in Quillette titled “The New Evolution Deniers, because it accuses the left of promoting an anti-evolution program of its own.

        Colin Wright, who authored the Quillette article, argues vehemently that “while …right-wing anti-evolution movements withered to irrelevance,  has been slowly growing.” Wright, who has a PhD in evolutionary biology from UC Santa Barbara, studies differences in behavior between males and females that biologists believe are evolutionarily determined. Trouble broke out, he says, when biologists extended these studies from insects, rodents, and non-human primates to humans. “The group that most fervently opposed, and still opposes, evolutionary explanations for behavioral sex differences in humans were/are social justice activists,” Wright charges.  

        At stake in what Wright is saying is more than a scientific debate about whether human males and females have biologically determined differences in behavior. That alone, of course, would be cause for controversy because many insist that such differences are matters of culture and socialization rather than genes and proteins. But beyond, that, Wright disagrees with the notion that binary sex itself is outdated. “We can acknowledge the existence of very rare cases in humans where sex is ambiguous, but this does not negate the reality that sex in humans is functionally binary,” he says. And perhaps most alarming is his contention that left-wing “activists” are suppressing the research that is needed to confirm the notion that human sex is binary (or as biologists say, sexually dimorphic).

Dichotomy versus Spectrum

        Here, Wright is going up against a trend among some medical scientists and biologists to see sexual identification as something that occurs along a spectrum rather than a dichotomy. He cites as an example of what he considers to be this misguided trend a recent editorial in one of the world’s two most prestigious scientific journals, Nature. The authors of that editorial decried a U.S. Department of Health and Human Services proposal, that they feel would, “establish a legal definition of whether someone is male or female based solely and immutably on the genitals they are born with. Genetic testing, [the proposal) says, could be used to resolve any ambiguity about external appearance”. The Nature editorialists say that such a method has no basis in science and…would undo decades of progress on understanding sex — a classification based on internal and external bodily characteristics — and gender, a social construct related to biological differences but also rooted in culture, societal norms and individual behaviour. Worse, it would undermine efforts to reduce discrimination against transgender people and those who do not fall into the binary categories of male or female.

        Wright disagrees. He believes instead that “Biological sex in humans…is clear-cut over 99.98 percent of the time.” But the Nature editorial claims that “By some estimates, as many as one in 100 people have differences or disorders of sex development, such as hormonal conditions, genetic changes or anatomical ambiguities, some of which mean that their genitalia cannot clearly be classified as male or female.”

        Wright believes that science is being sacrificed for political reasons when he states that “Despite the unquestionable reality of biological sex in humans, social justice and trans activists continue to push this belief [that sex is not binary] and respond with outrage when challenged. Pointing out any of the above facts is now considered synonymous with transphobia.”   The Nature editorial worries on the other hand that “Political attempts to pigeonhole people have nothing to do with science and everything to do with stripping away rights and recognition from those whose identity does not correspond with outdated ideas of sex and gender.”

Another Left against Right Scientific Debate

        Much has been written in recent years about the polarization of scientific misunderstandings along political lines. Liberals are supposed to be biased against vaccinations nuclear energy, and genetically modified foods, while conservatives are said to be biased against evolution, gun control, and climate change acceptance. When we at Critica review the scientific evidence, we invariably wind up being accused of political partisanship whichever side we come down on. Argue that the scientific evidence supports the safety of vaccines, nuclear energy, and GMOs and one is accused of being Republican. But argue that the scientific evidence supports the validity of evolution and climate change and the danger of personal gun ownership and we are accused of being Democrats. Hence, in some ways it was refreshing to see an argument that a traditionally right-wing point of view—evolution denialism—was also embraced by the left.

        But our main focus at Critica is trying to understand how best to convey scientific evidence to the public and here we have stumbled upon a seemingly treacherous field. There is no question that we should and must protect the rights of transgender and intersex people and everyone else who belongs to an oppressed minority, whether sexual or otherwise.   But we also want to be careful not suppress scientific inquiry in the service of ensuring that protection because ignorance and misinformation is never ultimately in any group’s best interest. As historian of science and philosopher Alice Dreger says in her book Galileo’s Middle Finger, “I want to say to activists: if you want justice, support the search for truth. Engage in searches for truth. If you really want meaningful progress and not just temporary self-righteousness, carpe datum [seize the data].”

What We Know About Sex

        So let’s step back a moment and consider what we do know about sexual differentiation in humans. Whether one is born male or female depends on the presence of a specific gene, the SRY gene, located on the short arm of a Y chromosome. Expression of the SRY gene causes the undifferentiated gonads to develop into testes and the production of testosterone, which leads to the “typical male genital phenotype. When no SRY gene (or functional Y chromosome) is present and there are two normal X chromosomes instead, “Female gonadal and phenotypic differentiation occurs…” This much is clear and irrefutable science.

        There are, however, a number of things that can occur to make that straightforward picture vary. Mutations in the SRY gene, for example, can result in an individual with the XY chromosomes typical of males but no testes, testosterone, or male secondary sex characteristics. There are many other such situations in which well-characterized abnormalities in genes, enzymes, and hormones lead to different phenotypes than traditionally considered male and female. Most of these phenomena are now well-characterized and detectable with modern diagnostic methods.

        A pressing question might be, how common is it that one of these events occurs? And more importantly, how many people are born with anatomies that are not typically male or female (i.e. intersex)? Wright says this happens only 0.02 % of the time; Nature (and Dreger) says it is more like 1%, a 50-fold difference.

It also turns out that reliable estimates of how many people identify as transgender are not easy to come by either. One study in the American Journal of Public Health estimated that one in 250 Americans (about 0.4%) identify as transgender.  However, the authors of that study cautioned that “It should be noted that this estimate may be more indicative for younger adults and… national surveys in the near future may observe higher numbers of transgender people.” They also point out that there are gender non-conforming people who do not identify as transgender and hence theirs is likely an underestimate of the true prevalence. The bottom line is that the true number of people who are either biologically not phenotypically male or female or who identify in non-conforming ways such as transgender is not known.

Is Science Being Suppressed?

        Not only does Wright believe that those who deny that human sex is dimorphic are wrong, he also charges academia with ostracizing biologists who adhere to the idea that human behavior is sexually dimorphic, that is, differentiated at least partially by the presence or absence of a Y chromosome. It’s hard to know how widespread such suppression of scientific opinion may be. Alice Dreger’s book is certainly replete with examples of scientists whose research on various aspects of human sexulaity have been met with what she believes to be politically motivated derision. “I had…stumbled onto…a whole fraternity of beleaguered and bandaged academics who had produced scholarship offensive to one identify group or another and who had consequently been the subject of various forms of shout-downs” (p. 108)

But on the other hand, we stumbled on a recent publication titled “Timing mechanism of sexually dimorphic nervous system differentiation”  that seems not to support Wright’s sweeping contention that research on behavioral sex differences in humans is universally beaten down by interest groups and universities. Now the work described in this paper was admittedly done with a type of roundworm called C. elegans that scientists are fond of and not in humans. Nevertheless, the study showed that a gene called Lin29 is present only in male brains and if missing leads to worms that have a male appearance but behave like a females. The same gene, the study’s authors point out, is also expressed in the human male but not female brain.  Perhaps even more interesting is that apparently the scientists involved in this study were not at all reluctant to openly discuss their findings in terms of genetically-encoded male and female behavioral differences. In an interview recorded in Neuroscience News, Oliver Hobert, the lead author of the study and a professor at Columbia University’s Department of Biological Sciences, is quoted as saying “If you look at animals, including humans, there are dramatic physical and behavioral differences between males and females, including, for example, how they move…The Lin29-deficient male worms, in essence, were feminized”.

        Does this openness about biology and dimorphic behavioral differences mean that Hobert and colleagues are not afraid of what Colin Wright calls the “left-wing activists who do hold power in academia?” Will they be accused of promoting an insensitive and unacceptable viewpoint for implying that there are two sexes among humans and that biology determines at least in part some aspects of how they behave? Or is Wright exaggerating the perils of studying the biology of sex-related behavior? Indeed, the Neuroscience News article was based on information released by Columbia University itself.

        The Wright article is important because it raises two interesting and important questions. First, is it the case that humans, like all other species, can for the most part be characterized as either male or female on a biological basis? And second, is there a powerful and organized left-wing evolution-denying cabal that is suppressing scientists who want to study that possibility?

        On both counts, it seems, we lack a lot of information. In terms of whether humans are truly dimorphic, Wright seems to be confounding what is biologically clear—that almost all humans either have or do not have a functioning SRY gene and therefore can be characterized at birth anatomically as either male or female—with a whole range of complicated emotional, cultural, and sociological influences that are uniquely human. There is little question, as the study on the Lin29 gene shows, that some aspects of human behavior are determined by genes that are differentially expressed in male and female brains. But we know very little about what causes Lin29 or the many other such genes in human brains that influence behavior to be expressed. We do know that environmental factors, many of which only humans experience, play a pivotal role in the extent to which any genes in our brains are active and therefore merely knowing the protein product of a gene in the human brain tells us relatively little about what influence it really has. Consequently, what determines sexually-related behavior is still unclear and likely far more complex that what our current knowledge of human genetics can tell us. Naturally, we favor allowing scientists as free reign as possible to pursue an objective search for what the evidence reveals about any topic, including how sex in humans can be determined and its subsequent influence on behavior. The results of such research may not appeal to all groups and organizations, but they will have to learn to live with what the science shows. It is perhaps perversely reassuring to us to learn that people of all political persuasions are capable of bias when a subject like evolution is concerned; maybe it is true that we can no longer ascribe all evolutionary denialism to right-wing thinkers. But we will need more evidence that accusations of transphobia and similar breaches of proper sensitivity are really being used to suppress valid evolutionary science in the academy.

        We conclude, therefore, that both sex and evolutionary denialism may reside on their respective spectrums. We need to encourage scientists to fearlessly probe every aspect of both spectrums in order to get the facts.


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