BIOLOGICAL SCHOOLS 31 



ing, as they do, questions as to what constitutes valid thinking and 

 what reliable evidence, are so fundamentally important that it is 

 necessary to consider them at some length. 



54. Students of heredity and evolution who think about, as 

 well as record, the facts they observe, are divided into schools, 

 some of which overlap ; for example, the selectionist, the muta- 

 tionist, the Mendelian, and the biometric. If these divisions 

 indicated merely associations of men who adopt different methods 

 of research, then, since a division of labour is advantageous when 

 dealing with a subject so large and difficult, the existence of 

 schools would be, not only harmless, but useful. Differences of 

 opinion could then be settled as they arose by a comparison and 

 sifting of evidence. But unfortunately the separation is some- 



of animals, so much the better can we apply the experimental method. In fact, 

 many of the problems of biology only become known to us as the result of direct 

 observation. The wider, therefore, our general information, the greater the 

 opportunity for experimentation. 



" It is undoubtedly true that many zoologists who have spent their lives in 

 acquiring a broad knowledge of the facts of their science fail to make use of their 

 information by testing the very problems that their work suggests. This is owing, 

 no doubt, to their exclusive interest in the observational and descriptive sides 

 of biology, but also in part, I think, to the fact that the experimental method 

 has not been sufficiently recognized by zoologists as the most important tool 

 of research that scientists employ. (T. H. Morgan, Experimental Zoology, p. 3.) 



" The essence of the experimental method consists in requiring that every 

 suggestion (or hypothesis) be put to the test of experiment before it is admitted 

 to a scientific status. From this point of view the value of a hypothesis is to be 

 judged, not by its plausibility, but by whether it meets the test of experiment." 

 (Op. cit. t p. 6.) 



" It is sometimes said that nature has already carried out innumerable and 

 wonderful experiments, and that we can never hope to excel her in this power. 

 Is it not better, therefore, to examine patiently and reverently what she has 

 done, and in this way learn how her processes have been carried out ? Let us 

 not be blinded by rhetorical questions of this kind. No doubt nature has carried 

 out prodigious experiments ; but we can never be certain that we know how she 

 has obtained her results until we repeat the process ourselves. What would 

 the chemist or the physicist say if he were told that nature has already carried out 

 experiments on a much greater scale than he can hope to accomplish, and that 

 he should drop his experimental methods and study his physics in a thunder- 

 storm and his chemistry in an eruption." (Op. cit., p. 8.) 



" If the truth must be told, the experimental method was given up for a long 

 time by the majority of specialists themselves in favour of the controversial, 

 and, indeed, this tendency has by no means yet died out among the habits of some 

 professed evolutionists. On the other hand, during the past fifteen to twenty 

 years, a few scattered workers have diligently applied themselves to the study of 

 the facts of variation and inheritance, with results which already more than 

 justify the anticipation in which their work was begun namely, that by such 

 methods alone can any real progress in our knowledge of the processes of evolution 

 be brought about." (R. H. Lock, Variations, Heredity, and Evolution, p. 3.) 



