Originally Posted by roseratlarge
1 sperm + 1 egg = fertilization
Only takes one
It actually requires a minimum of 5 million sperm for a successful vaginal fertilization; the vast majority of which are killed within minutes of entering the vagina. The 5 million number comes from fertility experts who have observed that men with lower sperm counts are very rarely successful.
Even when the sperm meet the egg, it takes many of them working in concert to open the egg. They use an enzyme located in their heads to dissolve the egg protective wall, but one sperm doesn't have enough enzyme to do the job. Eventually the wall weakens and one sperm enters. Very quickly the wall changes so no other sperm can enter.