INHERITANCE OF ACQUIRED CHARACTERS 71 
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- 29. 
