HI LECTURES ON EVOLUTION 83 



observation ; the other is the influence of sur- 

 rounding conditions upon what I may call the 

 parent form and the variations which are thus 

 evolved from it. The cause of the production of 

 variations is a matter not at all properly under- 

 stood at present. Whether variation depends 

 upon some intricate machinery if I may use the 

 phrase of the living organism itself, or whether 

 it arises through the influence of conditions upon 

 that form, is not certain, and the question may, 

 for the present, be left open. But the important 

 point is that, granting the existence of the ten- 

 dency to the production of variations; then, 

 whether the variations which are produced shall 

 survive and supplant the parent, or whether the 

 parent form shall survive and supplant the varia- 

 tions, is a matter which depends entirely on those 

 conditions which give rise to the struggle for 

 existence. If the surrounding conditions are such 

 that the parent form is more competent to deal 

 with them, and flourish in them than the derived 

 forms, then, in the struggle for existence, the parent 

 form will maintain itself and the derived forms 

 will be exterminated. But if, on the contrary, 

 the conditions are such as to be more favourable 

 to a derived than to the parent form, the parent 

 form will be extirpated and the derived form 

 will take its place. In the first case, there will be 

 no progression, no change of structure, through 

 any imaginable series of ages ; in the second place 



