Opinion | Wednesday, 1st May 2019

Caster Semenya: Researcher an expert witness in Olympic champion’s legal battle against IAAF rules

No one factor – such as testosterone levels – is responsible for athletic ability, writes sport scientist Dr Alun Williams

By Alun Williams

Reader in Sport and Exercise Genomics

I was recently called by a legal team to serve as an expert witness at the Court of Arbitration for Sport in Lausanne to act on behalf of the South African athlete Caster Semenya. She had challenged the International Association of Athletics Federations' (IAAF) new regulations on the eligibility of athletes with certain ‘Differences in Sexual Development’ (DSDs) and naturally high levels of testosterone to compete in the female category. 

The regulations state that some women with DSDs cannot compete in certain running events, or must have medical treatment to lower their naturally occurring high levels of testosterone for at least six months before competing.

My expertise lies within genetic characteristics of elite athletes and superior physical performance, and I have authored numerous scientific papers in this area. I used this research to demonstrate that the kinds of genetic changes in DSD athletes are comparable to genetic changes seen in other athletes that give them advantages over their competitors. In the context of sport performance, the mutations found in DSD athletes are not exceptional and arguably should not be treated differently by special regulations.

In my evidence, I also referred to the World Health Organization’s (WHO) guidelines that clearly state no single biological factor determines sex. Sex is determined by a combination of genetic and other factors, including hormone levels and anatomy. The WHO clearly states that while males usually have XY sex chromosomes and females usually have XX, there are also XY females and XX males.

There is a wide spectrum of DSDs that can involve either rare complements of sex chromosomes, for example, XXY or XYY, or rare mutations on other chromosomes that affect sexual development.  Thus, no single factor, genetic or otherwise, neatly determines whether an individual is male or female. Similarly, while research shows that elite men perform around 10% better than elite women, in many athletic events, no single factor such as testosterone level is wholly responsible for that difference.

However, the court found against the athlete Caster Semenya and in favour of the IAAF. For me, this decision defines the female category in sport via testosterone levels, but at the cost of the careers and livelihoods of DSD athletes. Only time will tell whether the regulation will be permanent or is challenged again.