Darwin, Variation of Animals & Plants
This illustration shows inherited traits in peas—some are wrinkled and others are smooth. In his book on variation, Darwin tried but failed to come up with a satisfactory explanation of heredity—the one aspect of his theory of evolution through natural selection that he could not satisfactorily explain. In Darwin’s (incorrect) theory of inheritance, called pangenesis, parts of the body gave off small particles (gemmules), which accumulated in reproductive organs and were transmitted in reproduction.
Charles Darwin (1809–1882). Variation of Animals & Plants under Domestication. London: John Murray, 1868.