You need the Real Audio player to hear this which you can download for free . If it still doesn't work try this link . Our body is made up of squillions of tiny cells, of many different types - brain cells, kidney cells, bone cells, muscle cells, heart cells, and so on. Most of this enormous research has been into how cells grow and live . But just recently, we've begun to look at the more interesting topic of how cells die.
Some cells have to die, so that other cells can live.
You can see this natural process of Programmed Cell Death in all living creatures. When a tadpole turns into a frog, the cells on the long thin tail of the tadpole have to die, to make way for the short stumpy end of the frog. Your hand originally starts off as a little flipper, and because cells decide to commit suicide in four neat little rows, you end up with five fingers on each hand. Ducks don't go quite as far, so they're left with little webbed feet. Your immune system knows the difference between you and the rest of the Universe, and tries to attack any of the rest of the Universe that comes inside your body.