Life (as we know it on earth today) only comes from preexisting life; we humans always start as fertilized eggs, which come from our parents, who came to be in just the same way; and so on back to the dawn of time. Yet, we all are mortal, and the continuous thread running through this succession is DNA, a self-replicating molecule that stores all the instructions, or perhaps contains all the ingredients, for making a new organism. The DNA molecules, in the form of chromosomes, are stored in cells, and animals and plants are built by cell division followed by cell specialisation. This means that the mechanism and control of cell division is one of the most fundamental aspect of biology. It also, of course, can go wrong with disastrous results, mostly in old age. Neither degeneration nor cancer are welcome. So, what do we know, and what would we like to know?