Death

 Death has been around as long as life. Early bacteria died because they ran out of food or water or because of hazards in the environment such as radioactivity or the great oxygen poisoning or viruses.

But in general bacteria do not die. Instead they divide into two daughters and so can be said to be immortal. What would happen to a bacterium which did not reproduce? It seems likely that it would die eventually, because of these environmental hazards. Life and reproduction are necessary for a cell to survive.

Eukaryotic Death

Early eukaryotes such as the protozoa, like bacteria, kept growing and dividing forever. More advanced eukaryotes, multicellulars, had cells which specialized. When cells specialize, for example swimming cells, they loose the ability to reproduce. Eventually they die. So the price cells paid for living together was that some of them died so others could reproduce. Only the reproductive cells managed to escape death. Eukaryotic cells seem to be programmed to die.

If living things did not die then all the carbon in the Earth would get tied up in their bodies. Also, if cells were immortal, there would be no raw materials left to make the next generation of life. Evolution would halt.