22 CONTACTS WITH DARWINISM I [ch. ii 



primitive genera the more widely distributed, and the most 

 highly modified the most local, taken together with other features 

 shown by the Podostemaceae, made the writer realise that in 

 trying to work evolution from the variety — which upon the 

 theory of natural selection was an incipient species — upwards to 

 species and further, we were trying to work it backwards. Once 

 this fact had been fully grasped, as it was about thirty-five years 

 ago, the theory of natural selection became for him a theory 

 which in its youth had done a marvellous piece of work, but had 

 exhausted itself in that effort, and was not likely to lead to any 

 further serious advances, as indeed had already been shown in its 

 breakdown in the study of adaptation in the last quarter of the 

 nineteenth century. 



During the six years that this work occupied, the writer had 

 frequent opportunities of visiting the tropical forest, and soon 

 realised that the struggle for existence was mainly among the 

 seedlings that tried to commence life upon any small spot upon 

 which, owing to fall of a tree, the breaking off of a branch, or for 

 other reason, there was rather more light than usual. But most 

 of the seedlings were of differing species, and commonly also of 

 different genera. And as never twice would the same assortment 

 of seedlings have to be encountered, and never twice the same 

 conditions of weather, it was impossible to see how slight varia- 

 tions towards adaptational advantage could be of any use. Mere 

 chance, as we have already pointed out (p. 3), must evidently be 

 the chief factor in determining the survivors. Ecological adapta- 

 tion to slight climatic and other changes must evidently be 

 internal rather than external. It was possible, as Harland has 

 suggested, that slight changes of this kind might entail some genie 

 change, and these, when added up over long periods, might give 

 rise to morphological mutations. But this has little or nothing 

 to do with the straightforward natural selection that was 

 normally accepted, and in any case is working downwards from 

 above, as does differentiation. 



The fiercest struggle for existence that a plant is ever likely 

 to encounter is that into which it must be thrown at its birth, 

 when it will have to compete with other seedlings upon land 

 already very fully occupied. Any form that is not adapted to the 

 conditions in which it finds itself at that time will be remorselessly 

 killed out, unless the time is short, hy reason of its unsuitahility ^ 

 and that is what natural selection really means. Anything that 

 is in any way handicapped — by unsuitability to the conditions, 



