It's one of those areas where blank slaters have so far been unable to insist on denying natural differences between men and women. No co-ed professional rugby, for example; and men and women are still separated in almost all team sports and track and field. The issue, of course, is testosterone. But what if someone is born intersex, gets an operation to become legally female but still seems to have enough masculine power to serve many other women off the tennis court? Meet rising tennis star Sarah Gronert, 22.