INTRODUCTION xiii 



If we can be satisfied that ever higher functions 

 have risen to dominance in the successive stages of 

 animal and human development, if we can further be 

 convinced that the sequence is irreversible, we shall be 

 convinced that future man will be more and more com- 

 pletely controlled by the very highest powers or aims 

 to which this sequence points. Otherwise we must 

 disbelieve the continuity of history. But the germs 

 of the future are always concealed in the history of 

 the present. Hence — pardon the reiteration — ^if we can 

 once trace this sequence of dominant functions, whose 

 evolution has filled past ages, we can safely foretell 

 something at least of man's future development. 



The argument and method is therefore purely his- 

 torical. Here and there we will try to find why and 

 how things had to be so. But all such digressions are 

 of smaU account compared with the fact that things 

 were or are thus and so. And a mistaken explana- 

 tion wiU not invalidate the facts of history. 



The subject of our history is the development, not 

 of a single human race nor of the movements of a cen- 

 tury, but the development of animal life through ages. 

 And even if our attempts to decipher a few pages here 

 and there in the volumes of this vast biological history 

 are not as successful as we could hope, we must not 

 allow ourselves to be discouraged from future efforts. 

 Even if our translation is here and there at fault, we 

 must never forget the existence of the history. Some 

 of the worst errors of biologists are due to their hav- 

 ing forgotten that in the lower stages the germs of the 

 higher must be present, even though invisible to any 

 microscope. Our study of the worm is inadequate and 

 likely to mislead us, unless we remember that a worm 



