semen and sperm quantity
semen and sperm quantity are dependent on many factors: diet, life style, blood levels of certain hormones, minerals and vitamins, and heredity are some of them. The semen and sperm quantity can be increased by taking proper diet. also the correct proportion of minerals and vitamins are important.
It is true that only one sperm is needed to fertilize the egg but the normal range indicates the cahnces of pregnancy (more sperms may increase the chances) and at the time of fertilization, only one sperm binds to the egg but all the remaining sperms facilitate this process and help in this binding. This is a very complex process and comprises of several steps.