The htheritaiice of Acquired Characters 51 



assumption, not only in the restricted sense as defined above, 

 but also in the sense that external conditions may directly affect 

 the whole organism, i.e. germ-cells as well as the body-cells. 

 He made no such sharp distinction, however, between these two 

 sides of the question as we find it convenient to make nowa- 

 days. 



Let us examine critically the experimental evidence on which 

 the theory of the inheritance of acquired characters, in the 

 restricted sense, rests, for, could it be shown that changes 

 acquired through use are transmitted to the next generation, we 

 might seem to be able to explain how many of the complicated 

 adaptations and coordinations of animals have arisen. 



Amongst modern writers the first to seriously question the 

 truth of the generally admitted doctrine that acquired charac- 

 ters are inherited was August Weismann. In his essay ''On 

 Heredity," pubhshed in 1883, and in two subsequent papers 

 "On the Supposed Botanical Proofs of the Transmission of 

 Acquired Characters" (1888), and "The Supposed Transmis- 

 sion of Mutilations" (1888), Weismann challenged the ac- 

 cepted point of view. His conclusions have become common 

 knowledge, so that it will not be necessary to go over the ground 

 again. While many zoologists and botanists were convinced 

 by Weismann's argument, which seemed to show that the evi- 

 dence fails to support the view that acquired characters are 

 inherited, a few zoologists have always insisted nevertheless 

 that such characters are inherited, and a few investigators have 

 brought forward experimental evidence which they beheve 

 shows convincingly that changes brought about in the body 

 may be transmitted to the germ-cells. It is this experimental 

 evidence that I propose especially to consider. 



Darwin believed' that acquired characters are inherited, and 

 in the "Origin of Species," in the "Animals and Plants under 

 Domestication," and in the "Descent of Man" he accounts for 

 many adaptations in this way. Herbert Spencer, especially, 

 although not always with discrimination, used this hypothesis to 

 account for many structures and habits of animals and plants. 



