204 



SCIENCE 



[N. S. Vol. XXXI. No. 789 



and are generally only by-products of the 

 process of evolution— characters that be- 

 long for the most part to the dump-heap 

 of evolutionary advance; and whilst they, 

 like all characters, call for explanation, 

 the student of adaptation of the living 

 world (regarding adaptation, as the fun- 

 damental problem of evolution) will pass 

 them over as of trivial importance for his 

 ends.^ 



Our problem, then, concerns the adapta- 

 tions of species, and from this time forward 

 when I speak of the origin of species I 

 mean the origin of the adaptive characters 

 of species. 



Modern thought has rejected the theo- 

 logical view of the miraculous origin of 

 animals and plants, but philosophy still 

 discusses the question whether there is 

 something purposeful residing in matter 

 or controlling matter that has brought 

 about the adjustments between the animal 

 and its environment, while science turns 

 rather to the question whether adaptation 

 is not the result of a reaction between the 

 organism and the outer world; and if so, 

 in what sense we are justified in applying 

 chance to such a process. Let us examine 

 briefly the philosophical and scientific 

 points of view. 



"We have sufficient evidence to show that 

 animals and plants sometimes respond 

 directly in an adaptive way to changes in 

 their environment ; to such agents as food, 

 or light, heat and cold, moisture and dry- 

 ness. 



When we recall that since the first be- 

 ginning of life on the earth, plants and 

 animals have been subjected to these kinds 

 of physical influences, and the forms that 



"This statement is not, of course, to be under- 

 stood to underrate the great value of systematic 

 work; I wish only to emphasize that the evolution 

 of adaptive characters, rather than of systematic 

 characters, is the question of absorbing interest 

 to the naturalist. 



have persisted are those that have reacted 

 adaptively, it is not surprising that they 

 should respond at times, if not always, 

 adaptively even under new conditions. 

 The fact that some directly adaptive re- 

 sponses occasionally occur can not, how- 

 ever, be used as an argument that all 

 adaptive responses have so arisen. 



The adaptive response to poisons, or to 

 foreign bodies of any kind introduced into 

 the animal, is one of the most remarkable 

 phenomena of adaptation. In the great 

 majority of cases the response is specific 

 for a particular poison, and the poison, 

 such as abrin, may be one with which the 

 animal can have had no previous experi- 

 ence. A leading pathologist has not hesi- 

 tated to state in this connection : 



If our studies in infection and immunity have 

 any meaning, they teach us, that . . . adaptation 

 is primarily an active process or at least in- 

 evitable and in no sense subject to chance. It is 

 not the mere fortuitous, passive modification of 

 living matter in a favorable direction, but a 

 process whereby that living matter is able to a 

 greater or less extent to change and suit itself to 

 its environment. 



The adaptive character of these re- 

 sponses loses some of its mystery, although 

 none of its interest, if, as has been sug- 

 gested, the poison acts by becoming first 

 incorporated in the living tissue and the 

 living tissue in consequence sets free cer- 

 tain products of the reaction or possibly 

 products of its own bi-eak-down whose 

 presence in the blood serves to lock up the 

 poisonous substances. It has been sug- 

 gested that this process is similar in many 

 ways to the process of assimilation of food 

 by the organism. If this point of view 

 recommends itself, it shows how the organ- 

 ism is a machine already prepared to do 

 this sort of work, and the cases that fill us 

 with astonishment may turn out to be but 

 variations of a process essential to all 

 metabolism. 



