I think that question can be answered empirically. If you start with the assumption that players of both gender's push themselves to the maximum they can (i.e.

I think that question can be answered empirically. If you start with the assumption that players of both gender's push themselves to the maximum they can (i.e. they don't stop just because they are "good enough") then it's a matter of measurement... Take the max/mean/median/mode of a random sample of the stats you can find broken down by gender. If the female stats are close to the male stats then segmentation in that sport is probably artificial. However, my hypothesis (and I may get down-voted for this) is that for many sports the increased weight, height, and arm/leg length will provide an unfair advantage. I think your WNBA/NBA example may be a good example. But like all hypothesis it would need to be tested. Then we have the sports where there are no female leagues at all... for those, woman should at least be allowed to try out for the teams.