THEORIES OF HEREDITY 11 



conception of heredity, and therefore of evolution, than would 

 otherwise be possible. It will in fact serve admirably as an 

 introduction to the whole subject. After dealing with it we 

 shall be in a position to consider other aspects of the question 

 with advantage. 



18. Now, whether or not acquirements tend to be trans- 

 mitted, one thing is certainly true offspring often vary from 

 their parents, are often born different from what their parents 

 were at birth, even when no character has been transmitted. 

 Thus, for example, the child of normal parents may have a 

 sixth digit on one hand. But no one ever acquired a sixth 

 digit. All our knowledge of embryology tends to show that 

 a sixth digit, whenever it occurs, takes origin in the germ- 

 plasm. It is inborn from the first ; for it is wildly improbable 

 that a structure so complex can ever have been superimposed 

 on a normal hand by influences acting on the embryo or 

 foetus after it had developed from the germ. To take an 

 even more convincing instance ; all the members of a litter 

 of pigs, kittens, or puppies invariably differ, not only from 

 their parents but among themselves. It is impossible that 

 their differences can be due to the transmission of acquire- 

 ments, for in that case, since the sperms and ova were all 

 under practically identical conditions, every suckling, kitten, 

 or puppy would inherit nearly, if not quite, the same acquire- 

 ments, and therefore all would be much alike ; whereas the 

 fact is they may differ very greatly in size, shape, colour, and 

 a thousand other peculiarities. It is clear then that offspring 

 frequently we ought to say invariably vary from their 

 parents irrespective of the transmission of any acquirements. 



19. The question we have to consider, therefore, is not 

 whether all variations are due to the transmission of acquire- 

 ments, but whether any variations are due to such transmission. 

 The history of the question is instructive. Early in the last 

 century the philosopher Lamarck published a theory of evolu- 

 tion which assumed in effect that all variations are due to 

 the transmission of acquirements. His modern followers, 

 a dwindling body, assume that some variations arise thus. 

 Darwin started where the Neo-Lamarckians leave off. He 

 assumed that, while many variations arise apart from the 

 transmission of acquirements, some variations arise in con- 

 sequence of their transmission. His modern followers, the 

 Neo-Darwmians, who include the great majority of biologists, 

 go a step farther. They assume that no acquirements are 

 transmissible, and, therefore, that none of the variations of 

 the child are due to the inheritance of parental modifications. 



