Debates are raging again over who should be allowed to compete in women's sport. Take two recent examples that inflamed the Internet.

First the (London) Sunday Times reported that the International Association of Athletics Federations (IAAF) intended to classify women with higher natural testosterone as "biological males" - just as 800m runner Caster Semenya was headed to court to challenge IAAF regulations that would exclude her and others from competing owing to higher than typical testosterone levels. Then tennis great Martina Navratilova asserted that trans women "biologically, are still men", and shouldn't be allowed to compete in women's events.