Heredity 139 



as the science of the aimless (vestigial, abortive, atrophied, and 

 useless) organs and parts of the body. In all this I worked from 

 a strictly monistic standpoint, and sought to explain all biological 

 phenomena on the mechanical and naturalistic lines that had long 

 been recognised in the study of inorganic nature. Then (1866), as 

 now, being convinced of the unity of nature, the fundamental identity 

 of the agencies at work in the inorganic and the organic worlds, 

 I discarded vitalism, teleology, and all hypotheses of a mystic 

 character. 



It was clear from the first that it was essential, in the monistic 

 conception of evolution, to distinguish between the laws of con- 

 servative and progressive heredity. Conservative heredity maintains 

 from generation to generation the enduring characters of the species. 

 Each organism transmits to its descendants a part of the morpho- 

 logical and physiological qualities that it has received from its 

 parents and ancestors. On the other hand, progressive heredity 

 brings new characters to the species — characters that were not found 

 in preceding generations. Each organism may transmit to its off- 

 spring a part of the morphological and physiological features that 

 it has itself acquired, by adaptation, in the course of its individual 

 career, through the use or disuse of particular organs, the influence 

 of environment, climate, nutrition, etc. At that time I gave the 

 name of "progressive heredity" to this inheritance of acquired 

 characters, as a short and convenient expression, but have since 

 changed the term to " transformative heredity " (as distinguished from 

 conservative). This term is preferable, as inherited regressive modi- 

 fications (degeneration, retrograde metamorphosis, etc.) come under 

 the same head. 



Transformative heredity — or the transmission of acquired charac- 

 ters — is one of the most important principles in evolutionary science. 

 Unless we admit it most of the facts of comparative anatomy and 

 physiology are inexplicable. That was the conviction of Darwin no 

 less than of Lamarck, of Spencer as well as Virchow, of Huxley as well 

 as Gegenbaur, indeed of the great majority of speculative biologists. 

 This fundamental principle was for the first time called in question 

 and assailed in 1885 by August Weismann of Freiburg, the eminent 

 zoologist to whom the theory of evolution owes a great deal of 

 valuable support, and who has attained distinction by his extension 

 of the theory of selection. In explanation of the phenomena of 

 heredity he introduced a new theory, the " theory of the continuity 

 of the germ-plasm." According to him the living substance in all 

 organisms consists of two quite distinct kinds of plasm, somatic and 

 germinal. The permanent germ-plasm, or the active substance of 

 the two germ-cells (egg-cell and sperm-cell), passes unchanged 



