Originally Posted by
zanacal
I'm quoting an old post of Atomic's here - the same concept was also discussed in the past couple of days on the thread wondering how boy/girl twins are conceived:
'My own personal theory is, since X sperm are KNOWN to be slightly larger, they may be able to penetrate an egg singlehandedly or with very little help given enough time (it takes many many sperm to allow only one to fertilize the egg), while Y sperm, being smaller, may need or somehow be given a leg up by high numbers of sperm around the egg. Having less sperm around the egg may make it next to impossible for Y sperm to fertilize the egg and so the X wins by default, even if it takes several hours for it to burrow through the egg shell. No difference in the way they swim, their speed, their liking for pH, calcium, or anything...all those things do is just make it extra hard for ALL sperm to reach the egg, so less make it to the egg.'