500 STUDIES, SCIENTIFIC AND SOCIAL 



The Non-inheritance of Acquired Character. 



Doubt being thus thrown on the validity of the theory, 

 Mr. Galton suggested another, in which the germs in the 

 reproductive organs of each individual were supposed to be 

 derived directly from the parental germs and not at all 

 from the body itself during its growth and development. 

 A very similar theory was proposed some years later by 

 Professor Weismann under the now well-known term " the 

 continuity of the germ-plasm." Both these theories imply 

 that, except among the lower single-celled animals and in 

 certain exceptional cases among the higher animals, no 

 change produced in the individual during life, by exercise 

 or other external conditions, can be transmitted to its off- 

 spring. What is transmitted is the capacity to develop into 

 a form more or less closely resembling that of the parents 

 or their direct ancestors, the characteristics of these ap- 

 pearing in the offspring in varying degrees and compounded 

 in various ways, leading to that wonderful variety in 

 details while preserving a certain unmistakable family 

 resemblance. Thus are explained not only bodily but 

 mental characteristics, even those peculiar tricks of motion 

 or habits which are often adduced as proofs of the trans- 

 mission of an acquired character, but which are really only 

 the transmission of the minute peculiarities of physical 

 structure and nervous or cerebral co-ordination, which 

 led to the habit in question being acquired by the 

 parent or ancestor, and, under similar conditions, by his 

 descendant. 



Finding that this theory, if true, did not allow of the 

 hereditary transmission of the majority of individually 

 acquired characters, Weismann was led to examine the evi- 

 dence of such transmission, and found that hardly any real 

 evidence existed, and that in most cases which appeared to 

 prove it, either the facts were not accurately stated, or 

 another interpretation could be given to them. The trans- 

 mission had been assumed because it appeared so natural 

 and probable ; but in science we require as the foundation 

 of our reasoning not probability only, but proof; or if we 



