Thanks for that. The thing is that we all appreciate that this is a complicated and multifaceted issue, and on that basis testosterone is only part of the story. Another thing that is routinely considered, and has to be, is the non reversible effects of a male puberty. My body shape is fixed, it was laid down in puberty and adolescence and it cannot now be reversed by any hormones. This has to be borne in mind by the sporting authorities, and indeed generally is.
Elite sports people, regardless of their gender or sex, are by definition exceptional individuals. We can all go through dozens of them. Miguel Indurain, the cyclist, has enormous lung capacity, so big that it forces his other organs out of his ribcage and made him appear to have a belly even when he was at the peak of his fitness and below 5% body fat. In biological terms he was a freak. Many athletes are. Peter Crouch, the footballer, is enormously tall. Is this an advantage for a striker? It certainly helped him. The US basketball player who was recently imprisoned in Russia, Brittany something, is 6 ft 7. This is a woman, born a girl, and still exceptionally, freakishly, tall. (I use the word "freak" here in its biological sense, not its perjorative one). Jockeys are very small. Picking out an exceptional individual in order to make a point doesn't tell anyone anything. Elite sports people are ALL exceptional.
There are many factors that can convey a genetic advantage. Disproportionate numbers of male footballers have a third finger longer than their second, an unusual trait. Nobody knows why, except that it is genetically conveyed. Disproportionate numbers of Premiership/national team women football players are gay. Again, nobody knows why, but the variation from the mean is hugely significant and more than enough to indicate that there's a causal effect.
These genetic advantages are undeniable and they are simply a result of natural variation. If Peter Crouch comes up against a defender who is 5 ft 6, have a guess who gets the headers. That's competitive sport. It's fair that PC just happens to be enormously tall, that's just natural variation. However the considerations about trans athletes are about whether someone who has changed their gender by means of surgical or pharmaceutical interventions can then *fairly* compete against someone who has *not* had such interventions, and how this can be done in a logical and fair fashion. Surgical or pharm interventions for other purposes that convey an advantage are obviously excluded from all sports.
No. The observations I and others have made apply to either sex, any gender. It's about fair competition. It just happens that there are no sports I or others can think of where being born a girl and/or having female sex hormones conveys an advantage over being biologically male. Being born male certainly does, because by the end of puberty you are bigger and stronger than an equivalent female, and size and strength counts in more sports than not.