424 Ei7ner on G^^owth and Inheritance 



muscular and mobile. It is admitted even by Weismann's adherents 

 that the size and shajje of bones, the size and shape of muscles, are in 

 the individual modified bj^ the use which is made of them. It will 

 also probably be admitted that the modification is such as to facilitate 

 the operations in which they are used. Therefore, in every genera- 

 tion of woodpeckers — which birds, in the struggle for existence, had 

 to be content to pick up a living on tree-trunks, or starve — the con- 

 stant use of the tongue in extracting insects from holes in trees must 

 have elongated the tongue and hyoid bone, and increased the power 

 of protrusion of the organ in each individual. The Neo-Lamarckians 

 believe that these individual modifications were inherited in some 

 degree, so that a greater modification in the same direction was pro- 

 duced in the ofispring, and in this way it is easy to understand how 

 the degree of specialisation we now see was produced. 



* The Neo-Darwinians say that it is quite true that such modifica- 

 tions were produced by functional activity in the individuals, but these 

 modifications were never inherited ; other modifications of the same 

 kind arose by congenital [purely accidental] variation in some of the 

 same individuals, and the individuals that had these survived ; and 

 then the favoured individuals pairing together, some of their offspring, 

 inheriting from both parents, had the modification in a greater 

 degree, and so on ; which is very much like the argument that the 

 Iliad and the Odyssey were not written by Homer, but by another 

 man of the same name who lived at the same time. . . . Selection, 

 whether natural or artificial, is perfectly analogous to the process of 

 denudation in geology. It explains the extinction of innumerable 

 forms and the consequent gaps and intervals which separate species, 

 families, orders, etc., just as denudation explains the want of con- 

 tinuity in the stratified rocks. But geologists have never been blind 

 enough to suppose that the evolution of the structure of a given rock 

 was due to denudation ; they have always believed that the struc- 

 ture of each rock was due to the effects of the forces which have 

 acted upon it since its formation, and they have devoted their energies 

 to tracing by observation and experiment the effects of the various 

 forces.' 



The fact is, both the Neo-Lamarckian and Neo-Darwinian 

 theories are potent in attack, but impotent in defence. In 

 order to have a rational conception of nature, we need a 

 tertiuni quid to give solidity to the elements of truth they 



