What percentage of people are neither of the simple common XY nor XX chromosomes? It's about as many people as there are with red hair. If you don't include chimerics it's about 0.25-1.7%, if you do include twin chimerics it's 8%, not including mothers micro-chimerism.

Probably shouldn't be having those Kenyans (Kalenjin) competing in marathons either. Completely unfair advantage.

All models are wrong, some are useful.