OTHER THEORIES OF EVOLUTION 345 



generation to generation, but it is not a chemico-physical 

 impetus, but a psychological one (p. 91). It is not, how- 

 ever, like the conscious effort of the individual postulated by 

 Lamarckism. That is a force which can only act in the animal 

 kingdom, and then only on points accessible to the will. 

 Bergson's ' impulse ' is of far greater depth and influence than 

 the strivings of an individual will. 



This theory of life and its evolution is, of course, part of a 

 more profound system, the substance of which we cannot 

 discuss. The nature of the impulse is involved in his theory 

 of being and duration, and it is a question whether it can be 

 dissociated from it and stand alone as an explanation of 

 evolution apart from its metaphysical implications. 



Probably Bergson would not admit this. By limiting our 

 inquiry to the data of an historical process we are adopting the 

 procedure of the physical sciences, and in his view (p. 206) 

 the latter are incapable of dealing with life (cf. Russell, 1924, 

 p. 124). In any case we do not think we have the means for 

 judging the validity of this theory as an explanation of evolu- 

 tion. The most we could do is to express an opinion whether 

 life has the character of an independent force or whether it 

 is the product of its material basis. Lastly, we must point 

 out that, whatever the ultimate origin of the creative impulse, 

 the individual frequency and ' spread ' of modification have 

 to be considered. 



(b) Russell's ' psycho-biological ' viewpoint is at once 

 distinct from and similar to Bergson's theory. It envisages 

 the activity of a fundamental striving or horme as character- 

 istic of living as opposed to inorganic matter. He tries, like 

 Bergson, to show that this horme is, as it were, entangled in 

 the net of the inorganic, and that it is continually adjusting 

 itself to it by means of perception. This term is used in a 

 definitely psychological sense, ' but in a broad way to cover 

 all degrees of the receptive side of vital activity.' The results 

 of this activity are seen in both behaviour and morphoplastic 

 response, and the line between these is hard to draw. Behaviour 

 is held to have an influence over the executive organ. 



Russell does not consider the evolutionary aspect of his 

 problem (p. 133) ; but he admits that the individual activity 

 must be linked up with the larger process, and one is left with 

 the inference that evolution is a summation of individual 



