Hundreds of acrosomes must undergo exocytosis to digest holes in the zona pellucida. This is one case that does not bear out the adage, “The early bird catches the worm.” A sperm that comes along later, after hundreds of sperm have undergone acrosomal reactions to expose the oocyte membrane, is in the best position to be the fertilizing sperm.
—Human Anatomy and Physiology, 9th edition (Marieb)
I’m having trouble understanding why this would be the case—the last sentence, that is. Perhaps it does take a lot of sperm to break through the zona pellucida, but why would any sperm that comes after have an advantage? Do the sperm cells die after the acrosomal reaction? If not, can’t the first few sperm cells be the ones in best position to attach to the oocyte’s receptors once the zona pellucida has been penetrated with the help of other acrosomes from other sperm?
Moreover, are the acrosomal enzymes degraded? Why would there be a need to have so many acrosomes if the enzymes can continue working through the zona pellucida? All you would need is time and soon the zona pellucida would be broken down, even just by a low number of enzymes, would it not?