INHERITANCE OF ACQUIRED CHARACTERS 7* 



vidual are in any measure transmissible to descendants, 

 then all these co-adaptations, from the simplest up to 

 the most complex, are accounted for. In some cases 

 this inheritance of acquired characters suffices by itself 

 to explain the facts ; and in other cases it suffices when 

 taken in combination with the selection of favourable 

 variations. An example of the first class is afforded 

 by the change just considered ; and an example of the 

 second class is furnished by the case, before named, 

 of development in a deer's horns. If, by some extra 

 massiveness spontaneously arising^ or by the formation 

 of an additional " point," an advantage is gained either 

 for attack or defence, then, if the increased muscularity 

 and strengthened character of the neck and thorax, 

 which wielding of these somewhat heavier horns pro- 

 duces, are in a greater or less degree inherited, and in 

 several successive generations are by this process 

 brought up to the required extra strength, it becomes 

 possible and advantageous for a further increase in the 

 horns to take place ^ and a further increase in the 

 apparatus for wielding them, and so on continuously. 

 By such processes only in which each part gains 

 strength in proportion to function can co-operative 

 parts be kept in adjustment, and be re-adjusted to meet 

 new requirements. Close contemplation of the facts 

 impresses me more strongly than ever with the two 

 alternatives either there has been inheritance of 

 acquired characters, or there has been no evolution.'* 

 As we pointed out in the last chapter, there seems at 



* Herbert Spencer, 'The Inadequacy of Natural Selection,' 

 p. 20 



