World Athletics Championships: Man or woman? Why a genetic test is causing controversy in sports

This approach has been heavily criticized. Olympic long jump champion Malaika Mihambo told the Sport-Information-Dienst (SID): "A single genetic test sounds like a clear solution, but it's scientifically simplistic and ignores the fact that gender isn't a simple either/or." Even from a scientific perspective, the issue of gender isn't always clear-cut. Because every person is different, a clear distinction isn't so easy, says Olaf Hiort, head of the Department of Pediatric Endocrinology at the University of Lübeck and spokesperson for the Collaborative Research Center "Gender Diversity." He considers the SRY test "unethical."

The test, which has been used by the athletics association since September 1st, checks whether female athletes possess the so-called SRY gene. SRY stands for sex-determining region of Y and is usually located on the Y chromosome, but not always. In most cases, a Y chromosome and an SRY gene result in a male body type.

But the formation of biological sex is more complicated and begins around the sixth week of pregnancy. Those with the SRY gene in their genes produce – unless the gene is mutated – the so-called TDF protein. This protein initiates the formation of male sex organs during embryonic development. If the SRY gene is active and all subsequent biological steps function, a person normally develops with a male phenotype – that is, they have a penis and testicles and, from puberty onwards, a deeper voice and body hair. If the signal from the SRY gene is missing, a female phenotype with ovaries, vulva, and breasts normally develops.

In addition to the SRY gene, there are many other genes involved in sexual development. "We know perhaps 100 genes today, but we don't yet know how many there actually are," says Olaf Hiort.

As is often the case in biology, it's not quite that simple and not always clear-cut. People who are not clearly biologically male or female are grouped together under the term DSD. It stands for differences of sex development .

The development of the so-called gonads depends on TDF. TDF initiates the development of the testes; without TDF, the gonads develop into ovaries. Two important cell types then form in the testes, which in turn produce various hormones. Some inhibit the development of female reproductive organs, while others produce testosterone , which is then converted into the more potent dihydrotestosterone (DHT). This hormone is crucial for the development of the external male reproductive organs.

If the signals for male characteristics are missing, a female phenotype automatically develops. However, there are also people with XY chromosomes and so-called gonadal dysgenesis who then develop a uterus – despite the SRY gene.

Sometimes, however, the problem isn't the hormone itself, but rather that the body doesn't recognize it. In these cases, there's a mutation in the androgen receptor, to which testosterone and DHT normally bind, thus initiating male sexual maturation. In this case, the necessary hormones are present, but they can't transmit their effects via the receptor. In this case, too, the body lacks the "male" signal and automatically develops female characteristics, even though an SRY gene is present in the genome.

Take, for example, the Spanish hurdler Maria José Martínez Patiño. She has complete androgen insensitivity syndrome (CAIS), as reported by the Los Angeles Times . The Spanish national team excluded Patiño in 1986 after a sex test revealed she had the Y chromosome. This chromosome was long considered a clear indicator of biological maleness. How many people are affected by CAIS is unclear, because hardly anyone knows which chromosomes they carry in their cell nucleus. Those affected usually have internally located testicles and lack a uterus or ovaries. Therefore, they do not have periods. According to the new track and field rules, a person who is proven to have CAIS is allowed to compete in the women's category.

The first gender tests were introduced by sports associations in 1946. At that time, these consisted of an examination of the external genitalia. The idea that the presence or absence of a penis alone determines gender has now been clearly refuted. In people with DSD, the external genitalia can be ambiguous and range from "normal" female to "normal" male. According to Olaf Hiort, there are approximately 100 to 150 children with abnormal genitalia in Germany each year.

About one in 20,000 men has two X chromosomes

It's not only the external genitalia that can exhibit both male and female characteristics. In what's known as mosaicism, cells with and without a Y chromosome alternate within the same body. This is the case with the Dutch sprinter Foekje Dillema. In order to participate in the 1950 European Athletics Championships in Brussels , she was required to take a gender test. Because she refused, the Dutch Athletics Association banned her for life. With the consent of her family, scientists conducted a DNA analysis after her death. The results revealed that Dillema had an XX/XY mosaic, meaning her body cells were both male and female.

In 1967, the International Olympic Committee introduced chromosome analysis. Microscopic examinations were used to determine whether female athletes possessed two X chromosomes. If athletes competing in the male category had also been tested at that time, some of them might have been found to be female. Approximately one in 20,000 men has two X chromosomes. 80–90 percent of these cases occur because the SRY gene is located on the X chromosome instead of the Y chromosome.

Testosterone is the best-known male sex hormone. It is produced primarily in the testes. However, women also produce testosterone. In addition to the development of the sexual organs, the hormone also controls growth and muscle development.

In most cases, men naturally have higher testosterone levels. However, within the natural range, women's bodies also have higher testosterone levels. This condition is known as hyperandrogenism. This can have various reasons, some of which are not always related to sexual development.

One cause is alpha reductase deficiency. This is a deficiency of the enzyme that converts testosterone into DHT. Because female sex organs develop instead of male ones without DHT, affected children often have female genitalia. However, during puberty, testosterone levels rise sharply. The result: a deeper voice, body hair, and increased muscle mass.

The most famous example of hyperandrogenism is the South African runner Caster Semenya . She won two Olympic gold medals and three world championship titles in the 800 meters. After undergoing the relevant tests, the Athletics Federation required her to artificially lower her testosterone levels in order to continue competing in the women's category.

"Decreasing testosterone levels cause muscle loss," says Olaf Hiort. But there are always two things: a fundamental and a variable part of sexual development. Testosterone is variable. Simply lowering levels doesn't necessarily lead to a feminine physique.

The physician believes: "The strict binary in sports is – and the discussion shows this – insufficient." Sports want to draw a line where nature doesn't divide so sharply. Science cannot offer sports clear evidence that shows whether a DSD athlete has an unfair advantage over women – and perhaps never will. And the sports associations themselves have not yet found solutions that are less binary. And so, starting Saturday, athletes will compete as usual in two categories: men and women.