World Athletics have introduced regulations preventing female athletes with certain differences in sex development from competing in the female category. We argue these regulations are not justified and should be removed. Firstly, we examine the reasoning and evidence underlying the position that these athletes have a substantial mean difference in performance from other female athletes such that it constitutes an advantage, and argue it is not sufficient. Secondly, if an advantage does exist, it needs to be demonstrated it is unfair. (...) We argue the advantage would not be unfair because to say otherwise relies on a presupposition about whether these athletes are female, which involves contradictory and inconsistent definitions of sex. Thirdly, we contend that even if it is established that there is an advantage and it is unfair, the response of requiring athletes to take testosterone-suppressing medication is not appropriate and is unfair. (shrink)

Not all vertebrates share the familiar system of XX:XY sex determination seen in mammals. In the chicken and other birds, sex is determined by a ZZ:ZW sex chromosome system. Gonadal development in the chicken has provided insights into the molecular genetics of vertebrate sex determination and how it has evolved. Such comparative studies show that vertebrate sex‐determining pathways comprise both conserved and divergent elements. The chicken embryo resembles lower vertebrates in that estrogens play a central role in gonadal sex differentiation. (...) However, several genes shown to be critical for mammalian sex determination are also expressed in the chicken, but their expression patterns differ, indicating functional plasticity. While the genetic trigger for sex determination in birds remains unknown, some promising candidate genes have recently emerged. The Z‐linked gene, DMRT1, supports the Z‐dosage model of avian sex determination. Two novel W‐linked genes, ASW and FET1, represent candidate female determinants. BioEssays 26:120–132, 2004. © 2004 Wiley Periodicals, Inc. (shrink)