For those of us that aren't automatic Semenya haters or Semenya apologists, a little perspective and background is helpful.
Now one doesn't actually need to know Semenya's medical specifics to be able with good confidence to put a name to the condition.
Androgen insensitivity syndrome
http://en.wikipedia.org/wiki/Androgen_insensitivity_syndrome
read it, get educated, and then debate.
1)People with AIS are 46,XY = genotypic male. They might still retain some "male" features- more muscle mass etc
2)But because of AIS, many have a varied level of female external appearance -"phenotypic female" - and often raised female.
Bottom line: IAAF will let a person with AIS run as a female if THEIR CONCLUSION is that the person is not gaining a significant unfair advantage from the AIS.