176 WARFARE IN THE HUMAN BODY 



were working factors making blindly for balance and sym- 

 metry, for easy action rather than difficult, for peace 

 rather than war. Indeed, the most appalling comment 

 to be made on such a state of nascent society is not that 

 it was so peculiarly dreadful, or that it puts a strain on 

 the imagination to conceive it, but that after long ages we 

 see similar factors but little altered still at their work. 

 Peace conferences have their ancient analogues and, as 

 great diplomatists argued round Pliocene camp-fires, 

 so, when Paris itself lies under the sea, other diplomatists 

 will even then debate on ancient premisses, while 

 idealistic, contemporary historians throw doubts on the 

 recorded savagery of extinct Europeans. 



If the whole of this volume were not in the nature of 

 a plea for the use of the imagination in science, so long as 

 it is controlled by ascertained results in allied branches 

 of learning, I might have hesitated to use such arguments 

 or illustrations. But when there are problems to solve, 

 in which few if any direct observations can be made, and 

 in which documents are rare, it is necessary to employ 

 some such method as that known in mathematics as the 

 Inverse Problem of Perturbations. Uninterpreted altera- 

 tions in the orbit of one or more planets lead to the dis- 

 covery of another almost beyond the reach of the telescope. 

 If, indeed, Neptune had never been seen, the facts as to 

 its orbit and distance from the sun would have been almost 

 certain. Such a case presents striking analogies with 

 investigation into prehistoric times. We observe the 

 inexplicable present, and infer an adequate cause. If the 

 present view suggested no more than a possible explana- 

 tion of the remarkable change from such as Pithecanth- 

 ropus to the modern type of brain which, following 

 Keith, I believe to be of very early origin, it would, at 



