Planarians do not need donor organs – everything grows back.

Planarians are a group of flatworms. Flatworms were the first side-symmetrical animals, i.e. no longer spherical or tubular. Planarians live in water or in warm environments on land.

Because of their enormous regenerative capacity, planarians are a research object for stem cell researchers who are working on growing replacement organs for us. When planarians are cut into several pieces, each of these pieces develops into a complete planarian. Planaria can reproduce by planarian division. To do this, they cling to the bottom with their head and rear end and tear themselves in half. Ouch. Each half then grows into a whole planarian. This is perhaps even more unpleasant than a human birth.

Planarians that use this asexual method of reproduction (plan A) never age.

However, some planarians prefer sexual reproduction (plan B). And these planaria develop age-related problems and die. Their death is intentional. Sex and death are therefore closely linked. Anyone who has sex must age and die. Whether the planarians prefer sex or being torn apart depends on the parasite load of their habitat.

More on this in the chapter: Sex and death – Why sexuality