So, as you know, when a sperm cells (Male sex cell) meets the Egg cell (Female Sex Cell) it forms something called a zygote. And from that point on, the egg cell reproduces more and more (making more cells) in a type of cell called a stem cell, which can be used for anything the body needs. The newborn babies keep these cells up until birth or the incubation (growth of the baby in the mother's uterus), and then they are ready to be born.
