  At the heart of this debate is whether trans women enjoy an unfair advantage over cis female athletes (i.e. athletes who were assigned the sex of female at birth and whose gender identity is female). Some have suggested that testosterone has not been proved to provide an advantage in competition (Camporesi, 2016) or that the advantage it provides, even if unfair, may be tolerably unfair (Devine, 2019). Moreover, no attempt is made to regulate other biological and genetic variations that provide a clear performance advantage. For example, there is no attempt to exclude or regulate athletes with Marfan syndrome. However, the long limbs and flexible joints associated with that condition provide a clear advantage for swimmers, basketball players, and volleyball players. It has been suggested that, if there is no morally relevant difference between advantages that result from sex and those that result from other biological and genetic variations, why should testosterone levels be regulated when other such variations relevant to sporting performance are not (Camporesi 2017; Camporesi and Maugeri 2016)?