The beginning
In the first two days of life, the newly fertilised egg travels along the mother's fallopian tube to the womb. On its way, it divides to make a clump of 32 cells - the morula stage. If the early embryo splits into two clumps of cells before this stage, it can grow into identical twins. This is because every one of the cells in the morula could still become any part of the growing embryo.
