Somatoplasm

The arcs represent the somatoplasms of four individuals.

He^([Weismann]) proposed a one-way relationship between the hereditary material contained in the gametes (the germ-plasm) and the rest of the body (the somatoplasm). He recognised that the germ-plasm is continuous from generation to generation. In each generation it is responsible for forming the somatoplasm. Crucially, however, the somatoplasm does not influence the germ-plasm.

As dazzling as biology's accomplishments are in making sense of genes, biologists are still bewildered by the immortality of germplasm and the mortality of somatoplasm. Indeed, the problem of immortality would disappear if the situation were reversed and, instead of germplasm, somatoplasm were immortal. Why are germ- and somatoplasm different in this crucial respect? Weismann had proposed the existence of different germ- and somatoplasms in order to explain the results of experiments intended to test the Lamarckian principle of the "inheritance of acquired characteristics."