390 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 19 31 



my use of the phrase " adaptation to environment," and then to go 

 on to see whether any common factor can be found for the super- 

 ficially diverse means by which the living organism seeks to attain 

 this adaptation, before discussing any particular examples of adap- 

 tive mechanisms. 



By the term environment I mean that portion of its surroundings 

 with which an organism can enter into exchanges of matter and 

 energy. The limits of the environment may be hard to define and 

 will depend upon the particular exchanges which are being con- 

 sidered. In the more complex organisms one part may be the envi- 

 ronment of the rest. 



I shall use the term " adaptation " as implying broadly any means 

 by which an organism is enabled to survive in its surroundings, not 

 as an individual but as a species. The term so understood means not 

 merely the ability to survive, but the ability to survive without alter- 

 ation of certain characters. A moment's reflection will show that, by 

 this criterion, we have no convincing evidence that any living organ- 

 ism has 3^et proved itself to be completely adapted to its environment. 

 On every hand evidence is daily being brought to light of species 

 which have become extinct, and yet the members of every living 

 species must have descended, in unbroken succession, from individ- 

 uals of one or other of those extinct species. Those transient species 

 were obviously not completely adapted to their surroundings, but 

 there was within the living matter of the individuals which composed 

 them, some more effective type of adaptation which has enabled it to 

 survive the impermanence of its external form. 



The extinction of so many species has been due, not so much, per- 

 haps, to their inability to adapt themselves to their surroundings, 

 as to their inability to make their adaptions quickly enough to keep 

 pace with their changing environment. For, during the ages which 

 have passed since living forms first made their appearance, the nature 

 of their environment has, no doubt, altered as profoundly as have 

 the living organisms themselves. 



Even the simplest living organism seems to be much more com- 

 plex than any inanimate system of which we have detailed knowl- 

 edge. But there is no valid reason for supposing that processes other 

 than those which are described as physical or chemical play any part 

 in their fundamental reactions. We may, therefore, expect the 

 behavior of the living organism to show many similarities and 

 analogies to that of inanimate systems in their relation to their envi- 

 ronment. On the other hand, there are what at present seem to be 

 rather characteristic differences between the two types of system, 

 although, on close analysis, these distinctions become hard to dr^w. 



