It was something that occurred to me as a major oversight when the teacher explained it in what was probably not the best way. The fisher's principle link is exactly what I was asking myself. Never done probabilities/statistics though so any difficult concepts I am probably not going to get.
If there is a 50/50 percent chance that offspring could be either a male or a female (at least that's what my bio teacher tells me) then what are the chances that the male/female human population is (for the most part) split 50/50?