To make a baby, a sperm from a man's body needs to join with an egg from a woman's body, later forming a tiny cell that typically has 46 chromosomes. Normally, three things are necessary for human birth: an egg, a sperm, and they must come from two different bodies. In certain cases, multiple zygotes may be formed. The reproductive system differs between male and female infants, as males do not produce sperm until puberty. The process of making a baby is known to most, starting with sex and ending with a new life.