August 25, 1905.] 



SCIENCE. 



2u 



to some end which we can not foresee. It 

 must always- be profoundly interesting to 

 the mind of man to trace successive cause 

 and effect in the chain of events which 

 make up the history of the earth and all 

 that lives on it, and to speculate on the 

 origin and future fate of animals, and of 

 planets, suns and stars. I shall try, then, 

 to set forth in my address some of the at- 

 tempts Avhich have been made to formulate 

 evoluticnary speculation. This choice of 

 a subject has, moreover, been almost forced 

 on me by the scope of my own scientific 

 work, and it is, I think, justified by the 

 name which I bear. It will be my fault 

 and your misfortune if I fail to convey to 

 you some part of the interest which is 

 naturally inherent in such researches. 



The man who propounds a theory of 

 evolution is attempting to reconstruct the 

 history of the past by means of the circum- 

 stantial evidence afforded by the present. 

 The historian of man, on the other hand, 

 has the advantage over the evolutionist in 

 that he has the written records of the past 

 on which to rely. The discrimination of 

 the truth from amongst discordant records 

 is freciuently a work demanding the highest 

 qualities of judgment; yet when this end 

 is attained it remains for the historian to 

 convert the arid skeleton of facts into a 

 living whole by clothing it with the flesh 

 of human motives and impulses. For this 

 part of his task he needs much of that 

 power of entering into the spirit of other 

 men's lives which goes to the making of a 

 poet. Thus the historian should possess 

 not only the patience of the man of science 

 in the analysis of facts, but also the imag- 

 ination of the poet to grasp what the facts 

 have meant. Such a combination is rarely 

 to be found in equal perfection on both 

 sides, and it would not be hard to analyze 

 the works of great historians so as to see 

 Avhich quality was predominant in each of 

 them. 



The evolutionist is spared the surpassing 

 difficulty of the human element, yet he also 

 needs imagination, although of a dift'erent 

 character from that of the historian. In 

 its lowest form his imagination is that of 

 the detective who reconstructs the story of 

 a crime ; in its highest it demands the power 

 of breaking loose from all the trammels of 

 convention and education, and of imagin- 

 ing something which has never occurred to 

 the mind of man before. In every case the 

 evolutionist must form a theory for the 

 facts before him, and the great theorist is 

 only to be distinguished from the fantastic 

 fool by the sobriety of his judgment— a 

 distinction, however, sufficient to make one 

 rare and the other only too common. 



The test of a scientific theory lies in the 

 number of facts which it groups into a 

 connected whole; it ought besides to be 

 fruitful in pointing the way to the dis- 

 covery and coordination of new and pre- 

 viously unsuspected facts. Thus a good 

 theory is in effect a cyclopedia of knowl- 

 edge, susceptible of indefinite extension by 

 the addition of supplementary volumes. 



Hardly any theory is all true, and many 

 are not all false. A theory may be essen- 

 tially at fault and yet point the way to 

 truth, and so justify its temporary exist- 

 ence. We should not, therefore, totally 

 reject one or other of two rival theories on 

 the ground that they seem, with our pres- 

 ent knowledge, mutually inconsistent, for 

 it is likely that both may contain important 

 elements of truth. The theories of which 

 I shall have to speak hereafter may often 

 appear discordant with one another accord- 

 ing to our present lights. Yet we must not 

 scruple to pursue the several divergent 

 lines of thought to their logical conclusions, 

 relying on future discovery to eliminate the 

 false and to reconcile together the truths 

 which form;par,t of each of them. 



In the mouths of the unscientific evolu- 



