PREFACE vii 



to use the familiar ideas of atoms, molecules, colloids, chemical 

 and physical states of equilibrium, energy-transformations, 

 potentials, radiation, and so on. In the light of modern physical 

 theory, however, most of these concepts are derived ones, and if we 

 use them in speculations upon the nature of life, there may be 

 some crudeness in our statements. Thus, quoting a very good 

 modern statement as to the aims of biology * 



1. " Scientific biology is strictly deterministic. It admits the 

 possibility of only one result from a given set of antecedents." 



2. " Scientific biology endeavours to explain organic pheno- 

 mena on the basis of antecedent physical conditions, though 

 admitting that our knowledge of cause and effect is in the last 

 resort empirical, to the extent that much which happens could 

 not have been predicted in advance." 



3. " Scientific biology declares that vital phenomena are 

 chemico-physical in the sense that they are the inevitable out- 

 come of the particular material aggregations which we call 

 organisms." 



Now whether our knowledge can be regarded as proving the 

 above theses is the subject of the following chapters. We must 

 be very clear as to what is meant by " determinism," " antecedent 

 physical conditions," " cause and effect," and " particular 

 material aggregations." We have really nothing to do with 

 determinism because the concepts that we employ in discussing 

 our results are those of functionality, correlation, and proba- 

 bility. Determinism is a logical category, or perhaps convention, 

 and it is strict only in mathematics, where, since we make 

 the rules, the strictness of result is to be expected. We assume 

 determinism because it is our mental postulate, and also because 

 we find that it works more or less approximately in chemistry 

 and physics, and even in physiology, so that we can construct 

 and use machines and cure some oliseases. But it never works 

 out exactly, and our results always have the form V e, where 

 V is the value we adopt for something or other as the result of 

 experiment, and e is a " probable error." W^e never get a 

 unique biological result from a " given set of antecedents " : thus 

 the bodily characters of an individual animal may surely be 

 regarded as the result of the characters of its ancestry (which 

 are the " antecedents " ; but this individual result is only one of 



* F. B. Sumner, The American Naturalist, vol. lii., 1919, pp. 193-217;. 

 vol. liii., 1919, pp. 338-369 



