8 ESSAYS SCIENTIFIC AND PHILOSOPHICAL. 



the species, and the life potentially immortal would 

 actually be limited by natural selection. Nature 

 does not feed " useless mouths." The higher 

 organisms, then, contain the germ of death, not 

 because death is a primary necessity for living 

 things, nor because in them a distinction between 

 reproductive and somatic cells exists, but because 

 in the somatic cells the power of indefinite multi- 

 plication ceased to be of use, and so was lost. In 

 short, the death of the individual was for the good 

 of the species. 



Such is Weismann's theory of the origin of 

 death. And it is interesting to find that, more 

 than twenty years ago, Dr. A. R. Wallace had hit 

 upon a similar explanation. In a note written 

 some time between 1865 and 1870, but published 

 for the first time as a footnote in the present 

 volume, he says that while an organism, which 

 increases by fission, would survive in spite of the 

 destruction of its individual separated parts, those 

 organisms which give off very small portions to 

 form new organisms would be at a great disad- 

 vantage as compared with these smaller organisms 

 in the struggle for existence, and would soon cease 

 to exist : 



" This state of things," he says, " would be in any case for 

 the advantage of the race, and would therefore, by natural 

 selection, soon become established as the regular course of 

 things, and thus we have the origin of old age, decay, and 

 death j for it is evident that when one or more individuals 



