ARTICLES 



THE INHERITANCE OF ACQUIRED 



CHARACTERS 



By Prof. E. W. MacBRIDE, F.R.S., D.Sc, 



Imperial College of Science and Technology, London, 



The term " acquired character " is a rather ambiguous one. 

 Inasmuch as all the higher animals start their existence as 

 fertilised eggs of similar shape and of similar general structure, 

 though of very different sizes, as these eggs will fail to develop 

 unless external conditions are favourable, there is a sense in 

 which all the typical characters of the various kinds of animals 

 may be said to be " acquired." It was in this sense that 

 Prof. Adam Sedgwick used the term " acquired character " 

 in his article on " Embryology " in the nth edition of The 

 Encyclopcedia Britannica ; but it is, of course, not in this sense 

 that the inheritability of " acquired characters " has formed 

 the subject of controversy. 



Everyone recognises that, given healthy normal sur- 

 roundings, every kind of egg develops in a special typical 

 way ; for example, a perch egg develops into a perch, and a 

 shrimp egg into a shrimp, and so on. If circumstances are 

 changed and become unfavourable, the typical development 

 may fail to come to full fruition, and a stunted, half- 

 developed abortion may result ; but no change of circum- 

 stances will induce a perch egg to develop into anything 

 like a shrimp, or vice versa. But in certain cases, when the 

 typical shape has become well marked, a change of circum- 

 stances may produce some slight modification of the type ; as, 

 for instance, when cattle are driven up on to high cold moors, 

 and develop in consequence a thicker coat of hair, or when a 

 blacksmith by exercise develops abnormally the biceps muscles 

 on his arms. The belief in the inheritability of acquired char- 

 acters is a belief that changes in habit and in the environment 

 of the kind which we have just mentioned produce an effect, 

 not only on the animals directly exposed to them, but also on 

 their offspring. 



It is to be observed that the changes produced by an altered 

 environment are not to be thought of as the direct effects of 



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