138 LIFE AND DEATH. [HI. 



among the potentially immortal beings which would be damaged 

 in the struggle for existence, and would therefore be exposed 

 to still further injuries. The existing necessity for natural 

 death in all Metazoa might therefore be derived in an unbroken 

 line of descent from the first mortal Metazoan, of which the 

 death became inevitable from internal causes, before the prin- 

 ciple of utility could operate in favour of its dissemination.' 



In reply to this I would urge : that it has been very often 

 maintained that natural selection can produce nothing new, but 

 can only bring to the front something which existed previously 

 to the exercise of choice ; but this argument is only true in a 

 very hmited sense. The complex world of plants and animals 

 which we see around us contains much that we should call new 

 in comparison with the primitive beings from which, as we 

 believe, everything has developed by means of natural selection. 

 No leaves or flowers, no digestive system, no lungs, legs, wings, 

 bones or muscles were present in the primitive forms, and all 

 these must have arisen from them according to the principle of 

 natural selection. These primitive forms were in a certain 

 sense predestined to develope them, but only as possibilities, 

 and not of necessity; nor were they preformed in them. The 

 course of development, as it actually took place, first became 

 a necessity by the action of natural selection, that is by the 

 choice of various possibilities, according to their usefulness in 

 fitting the organism for its external conditions of life. If we 

 once accept the principle of natural selection, then we must 

 admit that it really can create new structures, instincts, etc., 

 not suddenl}?^ or discontinuously, but working by the smallest 

 stages upon the variations that appear. These changes or 

 variations must be looked upon as very insignificant, and are, 

 as I have of late attempted to show^, quantitative in their 

 nature ; and it is only by their accumulation that changes arise 

 which are sufficiently striking to attract our attention, so that 

 we call them ' new ' organs, instincts, etc. 



These processes may be compared to a man on a journey 

 who proceeds from a certain point on foot by short stages, at 

 any given time, and in any direction. He has then the choice 

 of an infinite number of routes over the whole earth. If such 

 a man begins his wanderings in obedience to the impulse of his 



^ See the preceding essay ' On Heredity.' 



