Mabch 25, 1904.] 



SCIENCE. 



495 



take for the future. I propose to discuss 

 now very briefly the principles which ap- 

 pear to me to be fundamental to a right 

 understanding of the nature of ecology. 



Principle 1. The Reality of Adaptation. 

 — To a first view it seems logically possible 

 that adaptation may have only a subjective 

 existence, and that the cases we consider 

 adaptations may be merely accidental cor- 

 respondences between certain features of 

 the organism and certain characteristics of 

 the environment, involving no real advan- 

 tage to the organism. Now there can be 

 no doubt that many cases commonly reck- 

 oned as adaptations are of this imaginary 

 nature (it could hardly be otherwise while 

 post hoc propter hoc is the prevailing type 

 of ecological reasoning), but that some of 

 our adaptations have an objective existence 

 is susceptible of direct proof. Thus the 

 mechanisms connected with cross-pollina- 

 tion in specialized orchids represent a 

 typical adaptation. If, without other in- 

 jury to the plant, these mechanisms are 

 prevented from operating, no seed is formed 

 and the result is disastrous to that race 

 of plants. Hence the advantage of the 

 mechanism is made manifest, and the real- 

 ity of the adaptation is proved. 



This case illustrates the fundamental 

 idea, and permits a definition, of adapta- 

 tion. It is an adjustment between some 

 feature of an organism and some charac- 

 teristic of its environment such that the 

 organism functions better than it could 

 did such an adjustment not exist. 



Principle 2. The Evolutionary Phylog- 

 eny of Adaptation.— hogically two views 

 are possible as to the phylogeny of a real 

 adaptation. (1) It may have developed 

 quite independently of any connection with 

 the environment it now fits and have come 

 into its present relation with that environ- 

 ment by a sort of sifting process permitted 

 by the constant movement or circulation of 

 organisms in nature, very much as a num- 



ber of vari-shaped blocks shaken in a box 

 having vari-shaped cells opening from it 

 would each come finally to fill the cell with 

 which it most nearly corresponds in shape. 

 (2) It may have arisen gradually, either 

 by innumerable fine gradations or by some- 

 what marked steps, in close touch with the 

 environment, which may be acting either 

 directly causatively or only selectively. 

 The former view has received its strongest 

 advocacy in the recent book by Morgan, 

 while the latter is that almost universally 

 prevailing, and, as I believe, correctly. 

 There is no doubt that some adaptation is 

 of the former sort; and in some phases of 

 ecology, notably in distributional phenom- 

 ena of ecological plant geography, it plays 

 an important role. But that adaptation is 

 usually and essentially of this character 

 seems to me wholly denied by the evidence. 

 There is not, so far as I know, any form of 

 proof that can be adduced to decide be- 

 tween these two possibilities, but there is 

 an argument from probability so strong as 

 to be practically conclusive. It lies in the 

 cooperation of many distinct features of 

 adaptation to fit a form to a very special 

 or unusual environment requiring simul- 

 taneous and different kinds of modification 

 in many parts. Thus, to take the case of 

 epiphytes (such as the tropical epiphytic 

 ferns), if these were adapted in but one 

 feature alone, such as the roots, it would 

 be logically quite possible that this kind 

 of root had arisen by some method inde- 

 pendent of contact with the environment, 

 and that this form having been brought 

 accidentally into this habitat persists there 

 because these roots fit that environment 

 better than any other. But the probability 

 that this adaptation of the roots has arisen 

 independently of the environment is greatly 

 weakened when we note that so different a 

 structure as the leaves are also, and equally 

 well but in a different way, adapted to this 

 habitat. And when, further, we observe 



