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What Is Caster Semenya?

There are many intersex conditions that make it difficult or impossible to assign a gender to those – perhaps including the newly crowned South African 800m world champion – who have them.

Written By: Ross Tucker, PhD

Caster Semenya has become an overnight sensation. Regrettably it has been for her role in sport’s biggest current controversy – the question whether she might in fact be biologically part male. Some have simplified this question to a debate over whether Semenya is male or female, which is incorrect. Rather, the true question is whether Semenya may be intersex, which refers to a condition where ambiguous genitalia are present, and the genes don’t match up with the physiological development and appearance, making the classification of the person as either male or female is very difficult.

Caster Semenya. Photo by: Photo Run.
Caster Semenya. Photo by: Photo Run.

Intersex conditions result from what are called disorders of sexual development (DSDs). Authorities have suggested three broad categories of this condition. The first is that of a masculinized female; the second is an under-masculinized male; and the third is true hermaphroditism. In Semenya’s case, it would seem that one of the first two categories – the masculinzed female or under-masculinized male – may apply.

The complexity of assigning sex can be daunting, and is even impossible in some cases. What follows is a very brief overview of some of the possibilities. If it leaves you feeling more confused than ever, then you’ve understood the complexities of sex verification more than most!

With A Spotlight Comes Scrutiny

Born and raised in a remote rural community in the Limpopo province of South Africa, Semenya shot to prominence by running 1:56.72 in Mauritius in July. Her star continued to rise in Berlin, until it emerged that her sex was being investigated by the IAAF. A gold medal later, an international fall-out and a desperately sad situation for Semenya, yet still no answer is in sight. So what is Semenya, and how might we know?

The typical response to the question is “just check,” and rather embarrassingly, many of the officials from Athletics South Africa have dared all to check Semenya for female genitalia. If only it were this simple; a well-known joke asks how you know the sex of a chromosome. Answer: pull down its genes. On both counts, sex determination is much more complex than this, and neither the genes nor the “jeans” have the answer!

On the first count, conventional wisdom says that males have an X and a Y chromosome (XY) and females have two X chromosomes (XX). The chromosomes determine whether you develop male or female reproductive organs. Unfortunately, the nice, clear lines we are taught to believe exist often become blurred, and you do get XY females and XX males.

A number of conditions can explain these aberrations. For example, sometimes, some cells are XX, but others are XY – this is called mosaicism, and depending on which cells you looked at, you might incorrectly conclude that a person is male or female. XX-male syndrome can also occur as a result of a transolcation (movement) of part of the Y chromosome that contains genes for male sexual development onto the X chromosome. The result is the presence of two X chromosomes (a female), with a gene that causes the development of testes, and the person will appear male but is in fact genetically female. If that is not complex enough, sometimes the growing fetus is exposed to too much testosterone, and develops male genitalia.

The same can happen the other way – too little circulating testosterone and a growing fetus that is XY (that is, male) may fail to develop male genitals, leading to a female appearance, despite an XY chromosome being present.

Another condition is androgen insensitivity syndrome (AIS), where the hormone testosterone is present, but has little to no effect because the receptors are insensitive to it. The result is that a person who is XY fails to develop as a male. The result? An XY female. This was one of the most common conditions identified by the IOC’s testing (until compulsory screening was scrapped), with seven of the eight “failed” sex tests in the 1996 Atlanta Olympics being accounted for by this condition. The IAAF allows athletes with this condition to participate as females, despite their being genetically male, highlighting how simple genetic analysis alone does not suffice.

Nor does external examination of the genitalia. In all the above examples, the genitalia may be ambiguous or the opposite from what would be expected from the genes, making the oft-cited (in Semenya’s case) “shower check” just about irrelevant. Perhaps the most famous case of an intersex athlete was Stella Walsh, a Polish sprinter who was the Olympic champion in 1932, and a runner-up in 1936. The 1936 race was particularly notable, since she was beaten by Helen Stephens of the USA, whom she accused of being a man. Autopsies on these two athletes, in the 1980s, revealed that both had ambiguous genitalia, though neither autopsy went into detail to establish the specific DSD.

History of Gender Verification in Athletics

These two examples highlight the problem with a straightforward observation, which is actually what the sex verification process used to consist of. When sex verification was introduced in 1966, female competitors had to stand naked in front of a committee and were subjected to inspection of their external genitalia, in what where called “nude parades”.

That ill-conceived standard was replaced by a chromosome test of sorts, which looked for something called a Barr Body, which only exists when there are two X chromosomes. As we’ve seen, those two X chromosomes don’t necessarily indicate female gender, and so this test was not accurate by itself either.

The limitations discovered in these early verification procedures are the reason the current sex verification process is so complex. It now involves a multidisciplinary approach, which includes genetic, gynecological, psychological, internal medicine and endocrine experts, and is only done when suspicion or a challenge arises (compulsory screening having been scrapped in 2000).

We’ve already explained why the first two specialists are needed. The internal medicine specialist investigates the presence of internal structures that are male or female, while the psychological assessment involves assessment of the brain, since testosterone and other sex hormones influence the brain as well.

Finally, there is an endocrine assessment, and this is where the real functional differences are often found. Endocrine experts assess hormone levels, and the biggest difference between males and females is the level of testosterone, and other hormones like it. Collectively, they are called androgenizing hormones, and they’re responsible for the biggest differences between men and women with respect to exercise.

Effects on Performance

These differences include stronger, larger muscles, lower body fat levels, and differences in the shape of the skeleton, including a larger jaw bone, narrower hips and broader shoulders. Other masculinizing effects, not related to performance, include deepening of the voice and the growth of facial hair, both of which were cited as “signs” in the case of Semenya, particularly after an interview with her spread like wildfire on the internet.

It is the effect of testosterone on muscle development that confers an athletic advantage to males (or, in theory, to intersex individuals, if it manifests as increased testosterone levels). Advantages also arise from testosterone’s effect on body fat levels and distribution, and the biomechanical advantage caused by narrower hips. A stronger skeleton also helps, particularly in running events.

So testosterone holds the key, at least to performance advantages. After all, both men and women have sought to abuse testosterone as a drug since the 1960s. Many of the East German women received such large doses in an attempt to improve their strength that they developed male characteristics. One, famously called Hormone Heidi, was shot-put athlete Heidi Kriegler, who became Andreas Kriegler after retiring.

Hormonal Conditions

By now, given the complexity of gender biology, you may not be surprised to learn that there are a few medical conditions that affect hormone levels quite separately from the genes. For example, in a condition known as alpha-5-reductase deficiency, males cannot convert testosterone into another hormone, dihydrotestosterone (DHT). That’s a mouthful, but let’s just say that DHT is a hormone that is responsible for the development of the external male genitalia, and so if you can’t make it, then you fail to develop male testes and end up with the appearance of a female. In fact, persons with this condition may have male genitalia, ambiguous genitalia, or female genitalia. However, because they still produce testosterone, they get all the other masculinizing effects.

If that is not enough, a number of other enzyme deficiencies can lead to under-masculinization of males or masculinization of females. Any single expert has a real chance of making a mistake, and only an integrated approach can reduce this likelihood. For Caster Semenya, this discussion will be academic, and traumatic, being played out on the world stage when she herself has lived for 18 years as a female.

In time, the outcome of the testing may be known (there is a chance it will never be known, since it is meant to be kept confidential. However, given the profile of the story, this would seem unlikely), and then the myriad of other conditions, not even touched on here, may come up again. For now, let’s just say the problem is infinitely more complex than a simple sneak peek, and wait on the authorities to take the next steps.


Ross Tucker, PhD, is an exercise physiologist based in Cape Town, South Africa, and coauthor of The Runner’s Body.