Caster Semenya and the Biological Justification for Sex-Segregated Sports

Over the years, I have written about the case of Caster Semenya--the Olympian and World Champion runner who has been excluded from running as a woman because she is a chromosomal (XY) male with a disorder (or difference) of sexual development.  The International Association of Athletics Federation (IAAF)--now named World Athletics--has banned her from running as a woman because she has the elevated testosterone levels of a man that give her an unfair advantage over women in athletic competition.

In her new book--The Race to Be Myself (Norton, 2023)--she says that her case is "about the struggle for universal human rights" (304); and for this reason, she has appealed her case to the European Court of Human Rights.  I have argued that the natural desire for sexual identity is one of the twenty natural desires of evolved human nature.  Semenya identifies herself as a "masculine woman" with the "natural body" of a chromosomal male with some of the bodily traits of a woman--such as a vagina but no penis (1-2, 173, 184, 279, 283, 303). She says that her body is not a man's body.  Nor is it the body of a transgender woman.  Does she have a natural human right to express her sexual identity as a "masculine woman" by competing athletically with other elite women runners?

I have argued that the natural desire for sexual identity is (mostly) binary.  For most of us, our biological sex is clearly male or female.  And for most of us, our gender identity corresponds to our sexual identity as male or female.  But in rare cases, an individual's sex is a biological mosaic of male and female traits.  Semenya is one of those rare exceptional cases, as she herself says.  Is it therefore fair to exclude her--as a chromosomal male with a female gender identity--from competing in women's races?  Should she either compete with other men, or artificially reduce her testosterone levels to the female range, and then compete with women?  Or should she compete in a third category--"intersex"?  There is a tragic conflict of desires here between Semenya's desire to run as a "masculine woman" in women's races and the desire of biologically typical women to compete with other biologically typical women.

Although I lean to the side of the IAAF in this debate, I see good arguments on both sides; and so, I remain undecided.

MORAL DISAGREEMENT AND VARIABLE DESIRES

The fundamental problem here is the moral disagreement that arises from naturally variable desires, and the need for prudence or practical judgment to resolve such cases.  I identified this problem in Darwinian Natural Right (44-49).

If the good is the desirable, and if there is a natural pattern of desires for human beings that includes the twenty natural desires, why do human beings fall into moral conflict?  The pervasiveness of moral disagreement is the one fact most often cited by proponents of moral relativism, who believe there are no natural, universal standards for resolving moral debate.  It does not follow, however, from the fact of moral controversy that there are no natural standards for moral judgment.

There are four sources of moral disagreement: fallible beliefs about circumstances, fallible beliefs about desires, variable circumstances, and variable desires.  In considering variable desires, we see both normal (typical) and abnormal (atypical) variation.  The normal variation arises from age, sexual identity, and individual temperament.  Natural human diversity is such that the young do not have exactly the same desires as the old, men do not have exactly the same desires as women, and individuals with one temperament do not have exactly the same desires as those with another temperament.  

The abnormal variation in desires arises from abnormality in innate dispositions or in social circumstances.  So, for example, while human beings are normally social animals with social desires that incline them to feel the pleasures and pains of those close to them, a few human beings are psychopaths who lack the social desires that normally characterize human beings, and these people are moral strangers who are not open to moral persuasion.

Intersex individuals like Semenya show an atypical variation in their desire for sexual identity.  Semenya's "natural body" (as a biological male with some female traits) inclines her to identify herself as a "masculine woman," who does not fit into the sexually binary categories of men's and women's athletics.

SEMENYA'S AMBIGUOUS SEXUAL IDENTITY

Here's how Semenya describes her sexual identity:

"I have what is called a difference in sex development (DSD), an umbrella term that refers to the varying genetic conditions where an embryo responds in a different way to the hormones that spark the development of internal and external sexual organs.  To put it simply, on the outside I am female, I have a vagina, but I do not have a uterus.  I do not menstruate, and my body produces an elevated amount of testosterone, which gives me more typically masculine characteristics than other women, such as a deeper voice and fewer curves.  I cannot carry a child because I don't have a womb; but, contrary to what many people think, I do not produce sperm.  I can't biologically contribute to make new life" (1-2).

Semenya says that at puberty, she developed typically masculine features, and she began fantasizing about girls.  She announced to her friends and family that she was "into girls" (54-55).  Later, she developed romantic feelings for a girl that she married.  At the marriage ceremony, Semenya dressed as a man, while her bride dressed as a woman.  She thought this was right because she had always been very masculine.  She and her wife now have two children by IVF.  She denies that she is a lesbian (193, 212, 248, 269).

Semenya's "difference in sex development" is 5a-Reductase 2 Deficiency, which is caused by a mutation in the gene encoding the enzyme 5a-reductase type 2 (5aR2).  5aR2 catalyzes the transformation of testosterone (T) to 5a-dihydrotestosterone (DHT), which drives the process of the sexual differentiation in the external genitalia during the development of the male fetus in the womb.  5aR2D in chromosomal males arises from deficient 5aR2 activity, resulting in decreased DHT levels.  Consequently, at birth, males will show ambiguous genitals--a micropenis or no penis and what looks like a vagina.  Sometimes, as in Semenya's case, these biological boys will be raised as girls.  But then at puberty, these biological males develop typically masculine features, because pubertal virilization is driven by elevated testosterone rather than DHT.

The circulating testosterone concentrations in Semenya's bloodstream is within the range for typical adult males (from 8 nanomoles per liter [nmol/L] to 25 nmol/L), which is much higher than the range for typical adult females (0.4 nmol/L to 2 nmol/L).  The International Association of Athletic Federations (IAAF) has said that this has given Semenya an unfair advantage in competing with women.  One can see this just by looking at the World Records for Running.  In every event, from the 100-meter race to the marathon, the world record times for men is lower than for the women.  For example, in Semenya's best event--the 800-meter race--the world record for men is 1:40.91, while the world record for women is 1:53.28.  The IAAF has pointed to scientific studies concluding that the primary reason for this large sex difference in athletic performance is exposure to high levels of endogenous testosterone in males beginning at puberty.  These male advantages associated with higher testosterone are considered the justification for sex-segregated sports (Hunter et al. 2023).  

In 2009, the IAAF told Semenya that she could compete in women's events only if she took estrogen pills that would reduce her testosterone levels to no more than 10 nmol/L for six months.  Notice that this is still far above the range for typical females.  In later years, the IAAF changed its regulations to drop the maximum level of testosterone first to 5 nmol/L and then to 2.5 nmol/L (Semenya, 195, 267, 299).  For over five years--from January of 2010 to August of 2015--Semenya took the estrogen pills.  By June of 2010, her testosterone had dropped below the 10 nmol/L maximum; and she was then free to run in IAAF races.  Once again, she was winning 800m races with good times like 1:59.90 and 1:58.16.  Any time under 2 is a good time for an elite female runner.  But still these times were well above her gold-medal-winning time of 1:55.45 at the Berlin World Championships.

After IAAF lost a court case in 2015 about their testosterone regulations for women, the regulations were dropped, and Semenya stopped taking the estrogen pills.  One year later, Semenya won the gold medal for the 800m at the 2016 Rio Summer Olympics with a time of 1:55.28.  8 women ran in the 800 meters women's final.  Of those 8, 3 of them were chromosomal (XY) males with disorders of sex development (DSD) who identify themselves as women.  Those 3 intersex women have levels of testosterone far higher than normal for women.  These 3 were the winners of the race: Caster Semenya (Gold), Francine Niyonsaba (Silver), and Margaret Nyaira Wambui (Bronze).  One of the women who lost that race--Great Britain's Lynsey Sharp--expressed her frustration in televised interviews with having to compete against intersex individuals with the unfair advantages that come from male testosterone levels.  She and other female runners called for the IAAF to impose new regulations that would ban biologically male DSD athletes from women's events.

In 2018, the IAAF announced new rules:  athletes with DSD competing with women in the 400m, 800m, and 1500m distances would have to lower their testosterone levels down to 5 nmol/L for a period of six months before they were eligible to compete.  Then, in the spring of this year, the IAAF announced new regulations requiring women with DSD to lower their testosterone to 2.5 nmol/L or below for a continuous twenty-four months.  Semenya is contesting those new rules in her appeal to the European Court of Human Rights.

THE IAAF'S BEST ARGUMENT

In her book, Semenya gives her version of her dispute with the IAAF as presented in 2019 at the Court of Arbitration for Sport in Lausanne, Switzerland (Semenya 274-88).  Reading this along with a recent article by scientists supporting the IAAF's position (Hunter et al. 2023) makes clear the best arguments on both sides of this debate.

The best argument for the IAAF is that the biological basis of sex differences in athletic performance show that biological males--including those with DSD--have an unfair advantage in athletic competition with women, and therefore fairness requires that these men be excluded from women's athletic events.

This argument makes three claims.  First, in elite athletic competition, the performance of men tends to be superior to that of women.  Second, a primary reason for this is the sex differences in anatomy and physiology as determined by sex chromosomes and sex hormones, so that adult men on average are typically stronger, more powerful, and faster than women of similar age and training. Third, biological males with DSD (such as 5a-reductase 2 deficiency) will on average have this male advantage over women in athletic competition.  Semenya seems to accept the first two claims, but she rejects the third one.

The claim of male athletic superiority is easily supported by glancing at the world records for athletics.  Consider just the racing events, for instance, in which all of the world record times for men are faster than those for women.  In the 800m race, the world record for men is 1:40.91, set by David Rudisha running for Kenya at the 2012 Olympic Games.  The record for women is 1:53.28, set by Jarmila Kratochvilova running for Czechoslovakia at the Munich World Championships in 1983.  In the Marathon, the world records were set just two months ago.  The men's record is 2:00:35, set by Kelvin Kiptum running for Kenya at the Chicago Marathon.  The women's record is 2:11:53, set by Tigst Assefa running for Ethiopia at the Berlin Marathon.

One good criticism of this kind of evidence is that what looks like a male superiority in biological ability is really only a consequence of the differences in the cultural circumstances of men and women.  For a long time, women have been discouraged from participating in athletic activity.  In 1896, at the first Olympic Games in the modern era (in Athens, Greece), no women were allowed to compete.  In 1967, Kathrine Switzer was the first woman to run the Boston Marathon as an officially registered competitor.  In 1984, the first women's Olympic marathon was held in Los Angeles.  It was not until 2021, that there were similar numbers of women and men at the summer Olympics in Tokyo.  So, historically, women have had much less time and opportunity to develop their athletic skills than the men have.

In 1992, the journal Nature published an article by two biologists with the title "Will Women Soon Outrun Men?" (Whipp and Ward 1992).  They pointed out that over the previous century, both men and women were improving their world record times in racing, but the rate of improvement for women was double that for men.  The predicted that if these trends continued into the future, the world record times for women in the marathon would be the same or better than those for the men by 1998.  They also predicted that the records in all other racing events would be no different for men and women by the middle of the 21st century.

This has not happened, however, because beginning sometime after about 1985, the rate of improvement in women's running times began to slow and level out, so that there has been no intersection with the times for men.  In all of the running events, the gap between men's and women's world records is narrower than it has even been, but it's still there.

The best explanation for this continuing performance gap, according to the second claim of the IAAF, is that this shows biological sex differences:

"Sex differences in athletic performance that involve strength, power, and/or endurance are sizable and determined by biological differences between males and females.  Adult men ov average are stronger, more powerful, and faster over short and long distances than women of similar age and training status.  The sex differences emerge with the onset of puberty, coinciding with the increase in endogenous sex hormones, in particular testosterone in males . . . . The sex differences in the world records and best performances of many athletic events that rely on endurance and muscular power ranges from 10% to 30%. . . . The largest sex differences are apparent for sports and events relying more on muscular power such as in weightlifting, jumping events, and short distance swimming. . . ." (Hunter et al. 2023: 2332-33).

On the other hand, sports that rely less on muscular power such as archery and shooting show minimal sex differences in performance.

But even if we agree with all this--that typically biological males tend on average to have an advantage in athletic competition over typically biological females--it's not clear that this must hold true for atypically biological males with DSD like Semenya.

 

SEMENYA'S BEST ARGUMENT

Consider what Semenya says here:

". . . The IAAF's position was that women with high testosterone levels had an unfair advantage equal to the advantage that male athletes had over female athletes.  On its face, this is ridiculous.  We are not men.  I am a great runner, and I train with men, some of whom I can maybe give a hard time to on my best day, just like any other elite female athlete could, but I have never been able to even approach an elite male runner's times.  Likewise, there are plenty of men who normal 'male' testosterone levels whose only hope of beating a female athlete with 'female' levels is in their dreams" (238).

In fact, Semenya observes: "The IAAF knew that not one woman with a confirmed DSD diagnosis had ever even approached the running times of male elite runners" (269).  If biological males with DSD have the same advantage as normal males over women in athletic competition, then why don't runners like Semenya achieve the same running times as elite male runners?  Since Semenya's running times are within the range of other elite female runners, that suggests that she does not have an unfair male advantage over her competitors.

To counter this argument from Semenya, some IAAF officials have accused her of cheating by running slower than what she is capable of, thus hiding the fact that she has the same male advantage as other elite male runners (Semenya 281-83).  But this is implausible.  Throughout her running career, Semenya's great ambition has been to break the world record time for the 800m in the women's event, but she has never done that.  If she was easily capable of breaking this record, why would she slow herself down and fall short of the record?

There is one alternative explanation.  Most men with normal male testosterone levels cannot run faster than elite female runners; and even most good male runners who can run as fast as elite women cannot run as fast as elite male runners.  Is Semenya a good male runner who is good enough to compete with elite female runners, thus showing his male advantage, but not good enough to compete with elite male runners?  If so, could this be true for other "46 XY males with DSD"?

I don't have good answers to those questions.

AN "INTERSEX" OLYMPICS?

In any case, we should consider that one way out of this debate would be to create a third category for sexually segregated athletic competition--"intersex" events in which atypicaly males/females could compete against one another.  This would be similar to what is done now with the Paralympic Games--a highly successful event for athletes with disabilities.

Kenya's Margaret Wambui--the biological male with DSD who won the bronze medal in the 2016 Olympic 800m event when Semenya won the gold--has proposed this.  But Semenya rejects it.

REFERENCES

Hunter, Sandra K., et al. 2023. "The Biological Basis of Sex Differences in Athletic Performance: Consensus Statement for the American College of Sports Medicine." Medicine and Science in Sports and Exercise 55: 2328-2360.

Semenya, Caster. 2023. The Race To Be Myself: A Memoir.  New York:  W. W. Norton & Company.

Whipp, Brian J., and Susan A. Ward. 1992. "Will Women Soon Outrun Men?" Nature 355 (January 2): 25.