278 THE WORLD OF LIFE 



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 Avhicli have oc- 

 curred during the thousands or millions of years of its exist- 

 ence as a species. This implies that, for all ordinary con- 

 ditions and all such adverse changes as occur but once in a 

 century of 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 inillions, 

 which they w^ere 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 ef- 

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

 happened because the changes were different in kind, as well 

 as in rapidity, 'from any of nature's changes during the whole 

 period of the development of existing species. 



But although I feel confident that the known amount of 

 variation would amply suffice for the adaptation of any domi- 

 nant species to a nomially changing environment, I admit that 

 there are conceivable cases in which changes may have been 

 so great and so comparatively rapid as to endanger the exist- 

 ence even of some of those species which had attained to a 

 dominant position; such, for instance, as the opening of a land 

 passage for very powerful new Carnivora into another con- 

 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. 



