xxiv INTRODUCTION 



organs of the body act on the whole in concert, or, to take 

 an instance of another kind, the successive operations of an 

 instinct, e.g. the spinning of a spider's web are nicely cor- 

 related with one another, though we cannot assume that this 

 adjustment is effected by intelligence. The term correla- 

 tion therefore serves, first, as a summum genus under which 

 all kinds of vital activity, conscious or unconscious, might 

 be subsumed, and secondly, as a standard by which they 

 might be compared, certain assignable differences in the 

 method and scope of correlation yielding the required 

 differences of type which are successively evolved. There 

 was here a standard measure for the evolution of mind, and 

 to carry it right through that evolution has been the prin- 

 cipal task. It was worked out in some detail for animal 

 psychology and for the transition to human faculty in Mind 

 in Evolution, published in 1901. For human evolution 

 the ethical side seemed most important, and this was worked 

 out in Morals in Evolution five years later. The data 

 are in all cases difficult to ascertain with precision, and the 

 analysis has required constant overhauling and restate- 

 ment. 1 The results are summarised, modified, and 



1 Animal Psychology had barely emerged as a science twelve years 

 ago, and there was little then to rely upon beyond the pioneer work 

 of Romanes and the judicious observations and careful reflections of 

 Mr. Lloyd Morgan. Mr. Thorndike's experiments, however, had laid 

 the foundations of a new method, which has been brilliantly developed 

 by a series of American observers and experimentalists such as Profs. 

 Yerkes, Jennings, Haggerty, Watson, Shepherd and many others. 

 Animal Psychology as it stands may fairly be considered the creation 

 of American science. I regret that owing to the extended field covered 

 in this book I am unable to deal worthily at present with this new 

 wealth of material, but it has naturally modified my old opinions on 

 several points, as is briefly indicated in its place. 



In comparative ethics again to the work of Post, Letourneau and 

 Sutherland, which were the best available surveys ten years ago, should 

 now be added the encyclopaedic researches of Dr. Westermarck, and it is 

 hardly too much to say that this subject has also definitely entered the 

 rank of the sciences. 



