NATURAL SELECTION 187 



Darwin himself and the imperfect nature of the evidence. 

 Nevertheless, the doctrine has not attained the status of a 

 universally accepted law, and this, we believe, is because as 

 strong a prejudice is brought to bear against it as for it, and 

 (for the relatively small body of highly critical students) because 

 of the intrinsic difficulty of obtaining the right kind of evidence 

 for either its rejection or its confirmation. 



It is a very unsatisfactory state of affairs for biological 

 science that a first-class theory should still dominate the field 

 of inquiry though largely held on faith or rejected on account 

 of prejudice. To be just, the biologist is not wholly to blame 

 for this position. Any attempt to bring the method of evolu- 

 tionary inquiry into line with that in use in more exact branches 

 of science and to formulate for it a logical system of proof must 

 recognise that the circumstances of animal and plant life and 

 its transformation are peculiarly complex. The number of 

 variables is so large that it is doubtful whether they admit of 

 treatment and presentation on the same terms as the data of 

 other sciences. If biology is not an exact science (an accusation 

 often made against it), this is largely due to the nature of its 

 data. At the very offset the units with which zoology and 

 botany deal are not exactly definable as regards their morpho- 

 logical, physiological and bionomic properties, as the limits 

 of species and varieties in terms of structure, habits, reactions, 

 etc., are very variable. Furthermore, the background of 

 natural forces, which, either directly or indirectly, is held to 

 modify animals and plants, is homogeneous neither in time 

 nor in space. Finally, the phenomena of growth and numerical 

 multiplication introduce other variables. It is thus hardly 

 to be expected that a ' cut and dried ' formularisation of so 

 many variables would be feasible. 



The fact that biological science and the study of evolution 

 in particular are embarrassed by the complexity of their subject- 

 matter affords one explanation of their defects. For the rest 

 it seems that the lack of the exact discipline imposed, e.g. by 

 mathematical procedure, has given rise to the looseness of 

 statement that is unfortunately characteristic of much bio- 

 logical thought. There is something also to be seen in the 

 pathetic trust in observation per se. Nothing else can explain 

 the fact that wholly inadequate data have sometimes been 

 brought forward in support of the adaptive origin of certain 



