If we count protein molecules, for example, as inhabitants, the average cell would have a population of about 10 thousand million - that's a thousand times the population of London. And yet cells can duplicate their entire contents and divide into two daughter cells in only a few hours. A fertilised egg becomes two cells, each of these divides in turn and before long there are millions of cells as they form the young embryo. In making a new living being, not all of the cells are used. Very large numbers of cells die, carefully committing suicide at the right place and at the right time, to ensure the correct patterning and organisation of the remainder.
Cells constantly produce molecules that ensure the survival of their neighbours.
Most cells only die when they begin to lose this support.