AUTOMATIC ACTION 249 



We do not know how the case may be among invertebrates, 

 but among vertebrates the evolution of the power of develop- 

 ing in response to the stimulus of use has been accompanied 



tendencies being products of evolution. In remote times the tendencies 

 resident in the germ-plasm of one or more species of unicellular 

 organisms underwent such changes as a result of evolution that the 

 products of division (the offspring) did not separate, but remained 

 adherent. Multicellular organisms thus came into being, and, as a 

 further result of evolution, underwent differentiation into innumerable 

 species. Plainly the changes throughout were in essence changes in the 

 germ-plasm. It so evolved, so changed its tendencies, that fit stimuli 

 caused it to produce, not comparatively simple unicellular organisms, 

 but more or less complex multicellular organisms. Lastly, as a further 

 result of evolution, the nature of the germ-plasm was so changed that 

 from it arose organisms the " inborn " characters of which were capable 

 of further development in fixed directions as a response to the 

 stimulus of use. These extensions of " inborn " characters which result 

 from use and which we term "acquirements," however, are acquirements 

 in a sense not more real than "inborn" traits are acquirements. Both 

 sets of traits are acquirements since both result from stimuli ; " inborn " 

 traits develop from the germ-cell and continue to grow under the 

 stimulus of nutrition ; in the case of certain of the characters of certain 

 of the higher organisms nutrition at a certain stage of development 

 ceases to be the stimulus for growth, and use takes up the task. When 

 considering questions of evolution and heredity we must for ever keep 

 our attention fixed on the germ-plasm. It is evident that two of the 

 principal events which have occurred during the history of life have 

 been (1) that change in the germ-plasm which caused it to produce the 

 "inborn" structures (physical and mental) of multicellular organisms, and 

 (2) that change which caused it to produce " inborn " structures which 

 possessed the power of undergoing further development under the 

 influence of use. The non-recognition of the fact that the latter change 

 in the germ-plasm is a high and a late product of evolution has involved 

 biology in endless confusion, and has led to the formulation of several 

 extremely erroneous hypotheses ; for example, the Lamarckian doctrine 

 and the subsidiary doctrines of mental evolution enunciated by Spencer, 

 Lewes, and Romanes. (See 431-6.) The main error underlying all 

 these hypotheses is the assumption that the power of making use- 

 acquirements is a property possessed by all living beings. As we see, it 

 is a property possessed only by some of the structures of some living 

 beings, and these the highest. 



Before a structure can be used it must exist and be capable of being 

 used. Therefore, in every individual all structures must develop up to 

 a certain stage without the influence of use. Thus, for example, all the 

 structures of the human embryo necessarily develop without use. Later, 

 after birth, use takes up the task for which nutrition is now insufficient, 

 and the continued development of most of the structures is due to its 

 stimulation. The development of the individual is a recapitulation of 

 the life-history. During the evolution of the race, structures capable of 

 being used must have been evolved before the evolution of the power of 

 developing still further under the influence of use was possible. The 

 new power was obviously of immense importance ; for structures that 

 possessed it became endowed with a species of unconscious intelligence 



