374 DARWINISM AND THE PROBLEMS OF LIFE 



have to give all animals a complex organisation, since 

 it always seeks the better adaptation of all animals. 

 But we still have protozoa living in a drop of water. 

 In fact, many highly organised animals have become 

 extinct, while their more simply constructed relatives 

 have survived. 



There may be occasions in which the more complex 

 organisms are at a disadvantage in comparison with the 

 simpler. Natural selection will then modify organisms 

 in the direction of greater simplicity. In our view of 

 the development of the earth there will really be such 

 a time one day. The water on our planet is constantly 

 decreasing, and the time will come when there will not 

 be sufficient left to support human life, when the bones 

 of the last man will bleach in the unclouded glare of the 

 sun. But in the last drops that will linger in holes in 

 the vast desert of the earth there will certainly still be 

 infusoria. After a time even these creatures will not 

 find water enough ; they will perish, and only simpler 

 organisms still will be maintained, until at last all living 

 matter has returned to its mother and changes into 

 lifeless mineral once more. 



The fact that there are to-day animals at such 

 different stages of organisation is due, as we now know, 

 to special accidents that isolated certain animals. Even 

 the step that seems greatest to us, the formation of 

 multicellular organisms, must have taken place at a 

 particular locality — whether it was that certain protozoa 

 reached running water and so the connected ones were 

 less easily washed away, or that they reached a pond 



