The dichotomy between germ line and somatic line, and the origin of cell mortality.

The germ cells of extant animals are potentially immortal, whereas somatic cells are mortal, that is, they are able to carry out only a finite number of divisions. In this article we propose an evolutionary interpretation of these differences. We assume that germ cells of the earliest metazoans inherited immortality from their unicellular ancestor, while somatic cells acquired mortality by gaining new functions. It follows that cell mortality was under genetic control from the beginning of metazoan life.