lO HISTORICAL INTRODUCTION TO THE 



pression in fundamental physico-chemical terms is a question of 

 its own, and one which has been much obscured by the introduc- 

 tion of what are ambiguously called ''mechanistic" explanations. 

 As Woodger's (1928) analysis has shown, the term "mechanistic" 

 as applied to biological phenomena may mean : either 



1. That the structure and function of living organisms is to be 

 completely explained in terms of "little bits of stuff pushing 

 one another about" in accordance with the classical laws of 

 mechanics; or 



2. That all the phenomena presented by a living organism are 

 ultimately capable of analysis in terms of the laws of physics and 

 chemistry; or 



3. That a living organism is in some sense analogous to a human- 

 made machine and that its processes are explicable in terms of 

 this analogy; or 



4. That the causal postulate is perfectly applicable to living organ- 

 isms and can be satisfactorily applied to the biological order of 

 things, whether or no the phenomena of the biological order can 

 ultimately be brought into line with physico-chemical phenomena 

 and prove susceptible of analysis in physico-chemical terms. 



The fourth of these alternatives is generally accepted, and, in- 

 deed, the whole science of causal embryology is based upon it. The 

 second alternative is also widely accepted, and is the only fruitful 

 working hypothesis for the biologist. It is clear, however, that it 

 may require modification, for further study, notably of the 

 phenomena of life, is likely to reveal new and hitherto unsuspected 

 physico-chemical properties of matter. Accordingly, it is necessary 

 to take physics and chemistry in the most extended sense. The ad- 

 vances made in physics itself have rendered the first alternative 

 untenable, and the third cannot pretend to have more value than 

 can ever be ascribed to processes of reasoning by analogy; thus, 

 what may be called the cruder mechanistic view embodied in 

 alternatives i and 3 may be excluded. 



