120 HUXLEY MEMORIAL LECTURES 



such or such determinate forms much more than 

 the movement through which life becomes more 

 complex and raises itself towards greater and 

 greater efficiency. A very simple rudimentary 

 being is as well adapted as a man to its environ- 

 ment, since it succeeds in living in it : why, then, 

 if adaptation explains everything, has life gone 

 on complicating itself, and, moreover, compli- 

 cating itself more and more delicately and 

 dangerously? Molluscs such as the Lingulae, 

 existing at the present time, existed also in the 

 remotest ages of the palaeozoic era. Why did 

 life go any further ? Why, if there is not behind 

 life an impulse, an immense impulse to climb 

 higher and higher, to run greater and greater risks 

 in order to arrive at greater and greater efficiency ? 

 I think it is hard to survey the whole of the 

 evolution of life without the impression that this 

 impulse is a reality. The error is to believe that 

 this impulse has projected living matter in a 

 single direction, that species are classified along a 

 single scale, that everything has gone on smoothly 

 and without let or hindrance. It is, on the con- 

 trary, obvious that the force I speak of has found 

 resistances in the matter it had to make use of; 

 that it has been obliged to split up I mean to 

 share along lines of different evolution the dif- 

 ferent tendencies it carried ; that on each of these 

 lines there is a crowd of failures, of deviations, 

 of reversions ; that many of these lines of evolu- 

 tion have not been able to go on very far; that 



