32 PROBLEMS OF EVOLUTION 



work she chooses the easiest method. The individuals who 

 so cumber the species have already ex kypothesi suffered much 

 from accident. Why not another accident to give them the 

 coup de grace, instead of waiting for the operation of natural 

 death ? Surely the younger and less battered members of the 

 species would be equal to the task. Is not this the method 

 by which sexual selection works ? Probably but a small per- 

 centage of wild animals die a natural death, though they are 

 all liable to it. The fact is, it is easy to show how Natural 

 Selection can lengthen the normal duration of life, till it is 

 sufficient to allow of the rearing of offspring. But how she 

 can shorten it is not so clear. 



Weismann's theory of the origin of death has brought out his 

 combativeness in a most remarkable way. He started with the 

 doctrine of the immortality of the unicellular organisms, showing 

 that those now in existence were but fragments of their prim- 

 eval ancestors brothers or sisters would be a more correct 

 term. But when Maupas proved that immortality was depend- 

 ent on conjugation, the ground seemed to be cut from under a 

 favourite theory. He refuses to budge from his position, but I 

 cannot but think that in doing so he is showing a great power 

 of fight rather than the judgment and reasonableness that science 

 demands. 



The view that amphimixis is useful only because it produces 

 variation cannot stand. All characters that are not maintained by 

 Natural Selection tend to disappear. Now species sometimes 

 live in an unchanging environment, so that for hundreds of 

 generations little or no variation is required, and yet no species 

 is known in which amphimixis, having become the rule, has 

 afterwards died out. 



After thus criticising Weismann I now proceed to give with 

 some diffidence my own view of the origin of death and of 

 variation. It consists only of ideas that are to be found in 

 Weismann's books, though not all accepted by him, applied 

 in a way that seems to me to explain the known facts. 

 The origin of death is a question of much speculative interest, 

 but it is of far greater importance to realise that varia- 



