The union of an ovule and a spermatozoon initiates a complex cell division process that will ultimately yield a new living being. In fact, all the body’s cells come from embryonic stem cells that must divide in a controlled and exact fashion to give rise to proper organ and tissue formation in the embryo. However, phenomena as yet understood by science include the way that stem cells manage to control this accelerated division process without losing control, as occurs with tumour cells, and how division speed is adapted to energy and molecular supplies.