Now, although the discussion in this thread is going in a entirely different direction, I want to correct this line "when you were concieved, there were around 1 mils of your borthers and sisters who competed with you, but what made you so special that you won the race". As far as I recall from the course in reproduction physiology, only one sperm makes it to the ova. There are various projective enzymes and caspases! ( I am not sure of capsase cascade, but I believe, since it induces the apoptosis, It is there too). in the uterine environment. The head region of sperm has to go through capacitation, with influx of calcium and activation of cAMP (cyclic adenosine monophosphate), a signal transduction pathway and thus release of acrosomal enzymes. So, I believe one sperm one ova leads to fertilization as far as I recall.