INHERIT AN'OE OF ACQUIRED CIL-UIACTERS 107 



gressive heredity, more or less taken for granted by writers of 

 the last centmy, was flatly denied by Dr. August Weismann, 

 w^ho insisted that it was necessary that the theory of the 

 inheritance of characters acquired in tlie hfetime of tlie indi- 

 vidual should no longer be accepted without definite j^roof. 



In the theory of heredity through the devc'l()])nient of the 

 germ cell controlled by influences exerted by structures within 

 the nucleus, Weismann found no room for the inheritance of 

 characters not preestablished within this germ. External in- 

 fluences in general cannot reach the germ cells, and throughout 

 nature the germ cells are elaborately i)rotocted from tlie direct 

 influence of external conditions. 



This attack upon an ancient theory rousc.'d its supporters 

 to defend their fr.ith and to search foi- evidence to support it. 

 A temporary division of naturalists into two scliools arose as a 

 result of this discussion. Those wlio l:eld with Lamarck and 

 Spencer that characters gained in tlie life time of the individual, 

 and not received from ancestors possessing them, l)ecame hered- 

 itary, were known as Neo-Lamai'ckians. Those who, with 

 Weismann, denied the existence of this factor and from a neces- 

 sity, real or fancied, laid special stress on the Darwinian principle 

 of natural selection, assumed the title of Neo-Darwinians. In 

 their hands the Darwinian principle became the all-})owerful 

 factor in evolution, a theory of Albnacht which was soon 

 questioned from other quarters and bv those not considered as 

 ^ Neo-Tamarckians. Prominent among the leaders of the Xeo- 

 Lamarckians were Herbert Spencer, Haeckel, Nageli, Cope, 

 Eimer, Hyatt, Gadow, Dall, Packard, and others. Among 

 the recognized Neo-Darwinia,ns were' Weismann, Wallace, Hux- 

 ley, Gray, Brooks, liankester, and others. 



After some vears of controversv, mostly theoretical, the dis- 

 cussion has been tacitly dropped by biologists generally. It is 

 recognized that the sole crucial test is that of experiment, tliat 

 experiment is not easy, inasmuch as it is v(M'y difficult to show 

 that any given trait in lieredity really belongs to the category 

 of acquired characters, and that in no case has it l-)een indu- 

 bitably sliown that any charactei not inborn has been inherited. 

 Moreover the studies of the germ cell and the j^liysical basis of 

 heredity tend to show that the structures of the germ cell are 

 more complex and that the processes of heredity are in a sense 

 more mechanical than could have been supposed in the time of 

 14 



