258 THE WORLD OF LIFE 



structures, would be considerably modified in a hundred or 

 a thousand generations, and we have no absolute know- 

 ledge that any great change would be required in less time 

 than this. 1 



Objectors always forget that a dominant species has 

 become so because it is sufficiently adapted to its whole 

 environment, not only at any one time or to any average of 

 conditions, but to the most extreme adverse conditions which 

 have occurred during the thousands or millions of years of 

 its existence as a species. This implies that, for all ordinary 

 conditions and all such adverse changes as occur but once in 

 a century or a millennium, the species has a surplus of adapt- 

 ability which allows it to keep up its immense population in 

 the midst of countless competitors and enemies. Examples 

 of such thoroughly well-adapted species were the American 

 bison and passenger pigeon, whose populations a century ago 

 were to be counted by millions and thousands of millions, 

 which they were fully able to maintain against all enemies 

 and competitors then in existence. But civilised man has 

 so modified and devastated the whole organic environment 

 in a single century as to bring about an extermination which 

 the slow changes of nature would almost certainly not have 

 effected in a thousand or even a million of centuries. This 

 happened because the changes were different in kind, as well 



1 A very familiar fact will, I think, show that a large amount of co-ordinated 

 variability in different directions does actually occur. First-rate bowlers and 

 wicket-keepers, as well as first-rate batters, are not common in proportion to the 

 whole population of cricket -players. Each one of these requires a special set of 

 co-ordinated faculties good eyesight, accurate perception of distance and of time, 

 with extremely rapid and accurate response of all the muscles concerned in the 

 operations each has to perform. If all the special variations required to produce 

 such individuals were set forth by a good physiologist in the detailed and forcible 

 manner of the passage quoted from Spencer about the giraffe, it would seem 

 impossible that good cricketers should ever arise from the average family types. 

 Yet they certainly do so arise. And just as cricketers are chosen, not by ex- 

 ternal characters, but by the results of actual work, so nature selects, not by 

 special characters or faculties, but by that combination of characters which gives the 

 greatest chance of survival in the complex, fluctuating environment in which each 

 creature lives. The species thus becomes adapted, first to resist one danger, then 

 another ; first to one aspect of the ever-changing environment, then to another ; 

 till during successive generations it becomes so perfectly adapted to a long 

 series of more or less injurious conditions, that, under all ordinary conditions, 

 it possesses a surplus of adaptation. And as this complete adaptation is as 

 often exhibited in colour and marking as in structure, it is proved that the 

 transmission of the effects of use and disuse are not essential to the most complex 

 adaptations. 



