HARDWICKE'S SCIENCE-GOSSIP. 



265 



NEO-DARWINISM, 



By a. G. TANSLEY. 



\Conii)tHcd JrojH p. 244.] 



R. FRANCIS GAL- 

 TON'S theory of 

 heredity has been 

 variously described 

 ; as " a modification 

 of Darwin's " * and 

 as "substantially 

 the same as that 

 of Professor Weis- 

 mann."t We shall 

 endeavour to show, 

 however, that 



neither of these 

 representations is 

 correct. Mr. Gal- 

 ton's theory, in- 

 deed, stands in an 

 important manner 

 intermediate be- 

 tween "Pangene- 

 sis " and " the con- 

 tinuity of the germ-plasm," but it is a perfectly distinct 

 theory. In 1872 the main ideas were promulgated, 

 but a fuller account was published in 1S76. 



Mr. Galton sets out with a conception of the organism 

 as composed of microscopic "organic units." He 

 does not distinctly state whether these correspond to 

 cells, but with our present knowledge it seems 

 probable that, in many cases at least, they would 

 have to represent portions of cells. This conception 

 he thinks is necessitated by the facts of the inheritance 

 of microscopic characters, and the inheritance of 

 these from different parents. He explains this by 

 supposing that each organic unit is developed from a 

 separate germ or "gemmule." The whole collection 

 of gemmules in the fertilised ovum he calls the stirp. 

 Hence we see that he adopts the preformation theory 



* Lloyd Morgan's "Animal Life and Intelligence," p. 135. 

 t Wallace's " Darwinism," p. 443. 



No. 324.— December 1891. 



to explain the problem of development. But as we 

 shall presently see, his hypothesis differs in an 

 important manner from the complete conception of 

 preformation adopted by Darwin, the destructive 

 criticism of which by Professor Weismann we have 

 already quoted. 



]\Ir. Galton argues from the transmission to off- 

 spring of latent characteristics, derived from ancestors 

 but not appearing in the body of the transmitter, 

 that many gemmules must remain altogether latent 

 during the lifetime. He conceives of the stirp as 

 dividing, before the beginning of embryonic develop- 

 ment, into two parts, first, those gemmules which are 

 predominant, and which enter upon embryonic 

 development, and secondly the "residue," which 

 remain latetit in the body, and frojn which the irpro- 

 diictive elements are mainly if not solely derived. 

 Here we are presented with an entirely new solution 

 of the problem of transmission. Mr. Galton explains 

 the difficulty by supposing not that the bearers of the 

 hereditary tendencies are redeveloped from the cells 

 of the body in each generation, but that there is a 

 continuity of gemmules from generation to generation, 

 and that the structure of each organism is built up 

 by certain representative gemmules, which achieve 

 development. Mr. Galton remarks that there are 

 two classes of facts of heredity : (l) the transmission 

 of inborn or congenital peculiarities, also congenital 

 in one or more ancestors, (2) the transmission of 

 those inborn peculiarities not congenital in ancestors, 

 but acquired owing to changes in the conditions of 

 life. He points out that Pangenesis was especially 

 devised to explain the latter class; but he remark 

 that the majority of these cases may be looked upon 

 as "a collection of coincidences," that it is "indeed 

 hard to find evidence of the power of the personal 

 structure to react upon the sexual elements that is not 

 open to serious objection," and that " we might almost 

 reserve our belief that the structural cells can react 



N 



