36 EVOLUTION 



kingdom had taken place entirely through the action of 

 external agencies upon plants. The soil, for example, 

 in which a plant grows has a direct influence upon its 

 form. Altitude, moisture, heat, and light are other 

 important factors, and the effect of their influence upon 

 the plant was supposed by Lamarck to be inherited. 

 The shape of irregular flowers was regarded as having 

 been directly caused by the strains and pressures 

 occasioned by bees and other insects whilst making 

 their visits in search of honey or pollen. 



Lamarck's theory turns entirely upon the question 

 whether acquired characters are inherited, and if so, 

 to what extent, since, if such inheritance is shown to 

 be extremely slight, the cause, though a true one, 

 may be insufficient to explain the effects attributed 

 to it. Now, theories of heredity apart, and leaving 

 aside the results of minute observations which had 

 not been made in Lamarck's time, the natural supposi- 

 tion undoubtedly is that acquired characters are 

 inherited just as much as any others. Given the ob- 

 served fact that offspring resemble their parents more 

 closely than they do other members of the same species, 

 it is natural to believe that the child will take after 

 the forms exhibited by its parents at the time of its 

 conception rather than after those shown by them at 

 any previous period of their lives. This seems to be 

 the natural view in the absence of any other evidence 

 for or against, and so accurate a thinker as Herbert 

 Spencer, writing before the publication of the ' Origin 

 of Species,' regarded the term inheritance as neces- 

 sarily implying inheritance of this particular kind. 



