Once fertilisation has taken place, the new cell, conceived by mother and father, is a new human being with a complete human genome. The zygote starts to divide and change very rapidly. The baby starts to grow once fertilisation has taken place and this does not stop until he or she is 18 to 20 years old!

There is no other point during the development of a baby in the womb which marks the change between one kind of being and another – from two separate cells (like sperm and ovum) to a new human being.