3i8 ESSENTIALS OF BIOLOGY 



to natural conditions and so increased distribution and dominance. 

 Then, it is said, '' over-specialization " followed, with failure of 

 the episodial organisms to adapt themselves to the natural con- 

 ditions. But there must have been a phase in the process when 

 satisfactory adaptation of structure (and assumed functioning) 

 had been attained. Why, then, did the organisms continue the 

 process of amplification to the phase when their structures had 

 become detrimental in the struggle for existence } It would 

 appear that some ifnpulse to elaboration of structure and function- 

 ing had been the prominent and inevitable process leading to 

 the episode. 



107. ON THE FUTURE OF THE EVOLUTIONARY 



CAREER 



No results of modern biology enable us to predict transformist 

 processes. It will be seen, on sufficient reflection, that so-called 

 Mendelian predictions of the results of breeding experiments are 

 only statements of the probabilities of the combinations of known 

 structural characters : they are entirely analogous to, say, the 

 results of drawing a sample from a box in which known numbers 

 of diflJ'erently coloured balls have been mixed. The new thing 

 in a transformist process is a mutation. Mutations appear with 

 the semblance of spontaneity. Such changes are said to be 

 physically " induced," say by exposing a breeding animal to 

 X-radiation, but the nature of the change cannot be predicted. 

 Evolution, as w^e have already pointed out, is essentially the 

 appearances of novelties in a process, and no hypotheses yet 

 formulated, whether these postulate the " induction," by the 

 " environment " of mutations, or the evolution of that which is 

 already '' involved " (as in the preformation speculations), or 

 whether they include the vague and confused notion of 

 ** emergence," can stand up to the test of prediction. 



loja. The Time-scale and Physical Conditions. It is 

 certain that evolution has been in operation for a period of 600 

 millions of years. It is probable that the physical conditions 

 throughout that period have been much the same as they are at 

 present and will be for some future period of the order of thousands 

 of millions of years. It may seem quite preposterous to attempt 

 to contemplate what will happen in the future in the light of our 

 knowledge of the past and from what little we know as to the 



