26 
R. Ruggles Gates. 
MUTATIONS AND EVOLUTION. 
By R. Ruggles Gates. 
CHAPTER I. 
Introduction. 
T HE adoption of experimental methods of evolutionary study 
early in the present century was accompanied by sanguine 
hopes that a general and universally applicable method of evolution 
might thus be discovered. But two decades of intensive experi¬ 
mental work with plants and animals has led to a greater diversity 
of opinion concerning evolutionary factors than ever before. 
Wherever a particular species or group of forms has been 
intensively studied, the results have illuminated a particular field 
of inquiry concerning evolution. But other results, dealing with 
organisms having different bionomic relations, have answered other 
questions and at the same time propounded new series of problems. 
While there has therefore been a great accumulation of data 
concerning the variations of organisms, the inheritance of char¬ 
acters new and old, and the relations and reactions of these 
organisms to their varied environments; yet this has led to no 
unitary result which can be universally applied. These experiments 
have rather served to emphasize the manifold character of the 
evolutionary process. 
Not only have various groups of organisms contributed their 
quota to this multifarious result, but different methods of 
experiment and different fields of observation have no less clearly 
tended to emphasize particular evolutionary factors. Individual 
bias has also of course played a part in the interpretation of many 
results. 
Important and valuable as these experimental studies have 
been in opening a new era of evolutionary investigation, and 
leading to very definite conceptions concerning heredity and many 
aspects of variation and distribution, yet I believe they have been 
perhaps most generally useful in a direction which has not as yet 
been recognized. For their very variety, apart from interpretations 
put upon them, is sufficient to show that in the search for one all- 
explanatory evolutionary principle, man is following an ignis fatuus. 
Darwin recognized this even in his day, for while he laid chief stress 
upon natural selection, he also relied upon the Lamarckian factor, 
