Analysis | August 9, 2025
At the end of July, World Athletics announced that it will require a once-in-a-lifetime SRY gene test for all athletes wishing to compete in the female category for world ranking competitions. The new rules come into effect from Sept. 1 of this year, making it a de facto requirement for the World Championships in Tokyo.
The topic of biological sex testing in athletes is a controversial one. Female sports divisions largely exist due to sex differences that give biological males a competitive advantage, such as high levels of testosterone that increase skeletal density and muscle mass.
We can likely unanimously agree that somebody who is a biological male and who identifies as male shouldn’t be allowed to compete in female divisions, but the decision on whether it’s fair becomes murkier when considering people who don’t neatly fit into one of these two categories. For example, individuals with medical conditions where they are biological males based on their chromosomes but express female external genitalia, or individuals who have an extra sex chromosome.
Honestly, I was tentative to write about this topic because it feels like no matter how neutral I try to remain, I will receive accusatory messages, similar to when I relayed simple COVID-19 data during the pandemic a few years ago.
My goal for this article isn’t to take sides or to say whether World Athletics is right or wrong. I simply want to give you the historic context of biological sex testing in sport and to help you understand what the SRY test is so that you can come to your own opinion.
What is the SRY Gene Test?
Humans have 23 pairs of chromosomes that contain all their genetic information. You receive one copy of these chromosomes from each of your parents.
One of these pairs determines your biological sex and is referred to as the “X” and “Y” chromosomes. Biological females have two X chromosomes while biological males have an X and Y chromosome.
This applies to most people in the population, but a small number of people have what are now referred to by researchers as disorders of sex development (DSDs). DSDs encompass a group of conditions that affect the development of the sex chromosomes or the external genitals.
People with DSDs may have:
- Ambiguous external genitals
- Delayed or abnormal puberty
- Sex chromosomes that don’t match the typical XX or XY patterns, such as Klinefelter syndrome (XXY), XYY syndrome, XXXY syndrome, or XXYY syndrome.
The term DSD is now typically preferred over intersex in medical contexts, including eligibility guidelines for sport.
Estimates on how common DSDs are vary, but might be around 1 or 2 cases per 10,000 live births, or roughly 0.01 to 0.02 percent of the population. The highest recognized estimate puts this number at 5 to 170 cases per 10,000 live births.
The SRY gene test is performed with a cheek swab or blood test to look for the presence of sex-determining region Y protein (SRY) found on the Y sex chromosome and coded by the SRY gene.
It’s not found in females with XX chromosomes but is found in some people with DSDs.
SRY plays an important role in the development of the male genitalia while you’re in the womb, but a malfunction of this gene may lead to incomplete or improper development.
Why Is World Athletics Bringing in a Mandatory SRY Test for Female Athletes?
At least in athletics, the issue of fairness in sport effectively only goes one direction since there’s no evidence that being biological female gives an advantage over being male. It’s plausible that this could be the case in some other sports, especially where having a low body weight is advantageous, but that’s outside the scope of this article.
The mandatory SRY test has ostensibly been brought in to try to maintain fairness in the female categories. As reported in World Athletics’ press release, the president of World Athletics, Sebastian Coe, said:
“The philosophy that we hold dear in World Athletics is the protection and the promotion of the integrity of women’s sport. It is really important in a sport that is permanently trying to attract more women that they enter a sport believing there is no biological glass ceiling. The test to confirm biological sex is a very important step in ensuring this is the case.
“We are saying, at elite level, for you to compete in the female category, you have to be biologically female. It was always very clear to me and the World Athletics Council that gender cannot trump biology.”
It’s still worth noting that World Athletics also restricts participation in the male category to biological males and females who have used testosterone as part of male-affirming treatment.
Has Biological Sex Testing Been Used Before?
Biological sex testing in competitive sport isn’t a new concept, and it dates back to at least the early 1900s.
At the Olympic level, the issue first arose ahead of the 1936 Olympics held in Berlin. Stella Walsh, a Polish-American athlete, had already won the gold medal in the 100-meter dash in Los Angeles four years before. She had a muscular build and facial characteristics that prompted the press to give her the nickname “Stella the Fella,” and she was publicly accused of being male.
Walsh would finish second to Helen Stephens in 1936—another woman publicly accused of being a man. At the time, there was no formal gender verification program, but the Olympic Committee did perform a rudimentary “sex test,” which simply involved inspection of her genitals, which they confirmed were female.
After she died in 1980, post-mortem examination confirmed that she had ambiguous genitalia and abnormal sex chromosomes, although which DSD she may have had was not established.
The Introduction of “Nude Parades”
Many other controversial cases would appear over the next thirty years until a very low-tech sex verification system was introduced prior to the 1966 European Championships.
Here, female athletes stood naked in front of a committee and had their external genitals examined. Of the 243 women present in this first examination, none were barred from competition. However, notably, a pair of Russian sisters, Irina and Tamara Press, didn’t appear in the examination. They had set 26 world records in athletics between them and never competed in athletics again after the introduction of the examination. It’s been widely speculated that this may mean that they had DSDs, but this has never been proven.
Not surprisingly, these “nude parades” were criticized for being demeaning to the athletes and only lasted a few years.
Change to Lab Testing
Ahead of the 1968 Olympics, the process was switched to a “Barr body” detection test, which used a cheek swab to determine biological sex. The test works by looking for a genetic marker called the “Barr Body,” which is only found in cells with XX sex chromosomes.
Although arguably a better system than the previous genital inspection test, the Barr Body test had its issues.
Since it relied solely on the presence of a certain chromosome marker, people with XXY chromosomes and very high levels of testosterone would be able to compete since they had two X chromosomes, but people with a condition called complete androgen insensitivity syndrome, which likely wouldn’t provide an advantage, would be banned.
This new test led to the disqualification of the Polish Sprinter Ewa Klobukowska, who had won the European Championships in the 100-meter and silver in the 200-meter. She was banned on the grounds of having “one chromosome too many.”
It’s believed that she had a rare condition called XX/XXY mosaicism, where some cells have XX chromosomes and some have XXY chromosomes. She passed the anatomical test in the “nude parade” the year before and would later mother a son.
After her case, the IOC began keeping test results secret to protect the athletes from humiliation.
Change to SRY Test
In 1991, the Barr Body test was replaced with analysis of the SRY gene. At the 1992 Barcelona Olympics, 2,000 women were tested, and 15 tested positive for the SRY gene. In Atlanta in 1996, 8 of 3,000 tests were positive for this gene. Of these eight athletes, seven were found to have androgen insensitivity syndrome.
The testing was suspended in 1999 after years of debate, but the IOC maintained the authority to request it on a case-by-case bias.
Who Does the New SRY Testing Rules Affect?
World Athletics outlines the sex requirements for competition in Eligibility Rule 3.5, which is effective as of September 1.
In this eligibility rule, “biological male” refers to a person with a Y chromosome and ‘biological female’ means someone with no Y chromosome, irrespective of their legal sex and/or gender identity.
Requirements for the female category.
According to rule 3.5.2, only the following athletes may compete in the female category:
- A. Biological females.
- B. Biological females who have used testosterone as part of male gender affirming treatment further to a Therapeutic Use Exemption granted in accordance with World Athletics’ Anti-Doping Rules may not compete in the female category until the passing of a period of time after their last use of testosterone (the period of time will be not shorter than four years and will be determined by World Athletics on a case-by-case basis taking into consideration all relevant factors including the timing, duration, dosages, and effects of the male gender-affirming treatment).
- C. Biological males who have Complete Androgen Insensitivity Syndrome and therefore have not gone through male sexual development including any type of male puberty.
- D. Biological males with a difference of sex development who satisfy the transitional provisions issued by World Athletics.
Androgen hormones include testosterone and related hormones that give males masculine characteristics like body hair, testicle development, and a deep voice.
Category C Explained
Complete Androgen Insensitivity Syndrome is a medical condition where a person who is biologically male with testes and produces testosterone has malfunctioning receptors to these androgen hormones.
High levels of androgens in the womb normally cause male genital development, but resistance to androgens can cause female external genitalia to develop, despite having testicles instead of ovaries. Usually, people with this condition are raised female and identify as female.
While the World Athletics rules make an exception for complete androgen insensitivity syndrome if no male puberty has been achieved, it’s important to note that androgen insensitivity syndrome exists on a spectrum, and this represents the most extreme case.
Category D Explained
The transitional provisions in category D are a long list, but to summarize, it states that biological males with certain conditions who take hormone therapy to reduce testosterone can compete in the female category if they were previously eligible to compete in the female category before the rule changes.
This doesn’t apply to trans athletes. In 2023, World Athletics voted to ban transgender athletes from elite female competition if they’ve undergone male puberty. Research is still ongoing on the subject, but the decision, acknowledged by World Athletics as potentially contentious, came after some studies emerged suggesting that even after a year of hormonal therapy, transwomen may still maintain physical advantages over CIS women, at least in some metrics.
Criticism on SRY Gene test
In the World Athletics’ FAQ document, they state, “The SRY test is extremely accurate and the risk of false negative or positive is extremely unlikely.”
However, some experts have criticized the newly required SRY gene test under the pretense that it may be poorly executed, especially in developing countries, and due to potentially omitting some females from competitive sport who don’t have an inherent advantage.
In an article published earlier this week by Andrew Sinclair of the Murdoch Children’s Research Institute, he criticizes that science doesn’t support the assertion “The SRY gene is a reliable proxy for determining biological sex.” He takes the stance that the test shouldn’t be used to ban females from competition.
Sinclair was the lead researcher in a study published in Nature in 1990, where this gene was discovered and reported for the first time. He has continued to research other genes required for testicle development over the past 35 years.
In his article, he goes on to point out that although the SRY gene triggers a cascade of events during development that result in testicle formation, if the gene doesn’t function properly, a person can fail to develop testes and be biologically female despite carrying XY chromosomes.
Additionally, women who have complete androgen insensitivity syndrome with a functioning SRY gene have female external genitalia, but internal testes. Despite having testes, their tissues are unable to utilize excess testosterone.
Sinclair also points out that developing countries may not have the resources to send the samples to a lab, and processing by a male technician could contaminate the sample with skin cells that produce false positives.
Member federations are responsible for testing their athletes, and it’s fair to speculate that certain federations may not fulfil the requirements properly. Nigeria, in particular, has been under fire in recent years for making administrative errors that have barred their athletes from competition.
What Does SRY Testing Mean for Athletics?
SRY testing is theoretically being implemented to maintain fairness in the female categories.
There are some legitimate concerns that the test might not be the best way to determine which athletes have an advantage since it relies solely on chromosomes to determine eligibility and not other factors such as testosterone tissue sensitivity.
Unfortunately, no matter what method is used to determine eligibility, there will be some athletes left on the outside. There’s likely no perfect system, but it’s at least worth continuing to monitor the results of the testing protocol and revisiting it regularly to see if it’s achieving its desired goal of keeping a fair playing field.
The IOC has previously suspended mandatory SRY testing, so we may eventually see it scrapped by World Athletics if it isn’t found to achieve its goal.