564* POPULAR SCIENCE MONTHLY. 



LORD SALISBURY ON EVOLUTION.* 



By HEEBEET SPENCEE. 



ENTHUSIASTIC adherents have compared the principle of 

 natural selection with the principle of gravitation. The 

 comparison is not warranted. In the first place the one is far from 

 having a like cardinal value with the other as a scientific truth ; 

 and in the second place it is not the sole cause of the phenomena 

 to be explained, as Mr. Darwin himself admitted when recogniz- 

 ing the inherited effects of use and disuse. Nevertheless, after 

 making these reservations, I will for a moment adopt the compar- 

 ison ; because, by its aid, I shall be enabled clearly to show the 

 nature of a widely prevalent misconception. 



Let us suppose that our days were the days when Newton had 

 lately propounded his theory, and that the newspaper reader (or 

 as there were few such in those days, let us say " the man in the 

 street ") had been told about it. Suppose it had been explained to 

 him that, according to Newton, bodies attract one another directly 

 as their masses and inversely as the squares of their distances, 

 and that the phenomena presented by the Solar System had been 

 accounted for by him as conforming to this law. Suppose that 

 presently the man, thus far instructed, learned that there were 

 skeptics : Clairaut, for instance, having found that certain of the 

 Moon's motions could not be explained as results of gravitation, 

 and that consequently Newton's interpretation of planetary mo- 

 tions was untenable. Now suppose the man inferred that along 

 with the theory of gravitation the theory of the Solar System 

 must be abandoned; and that certain views of Copernicus, of 

 which he had heard, and certain other views of Kepler, had been 

 disproved. What, in such case, should we say ? Evidently that 

 the man made a profound mistake in identifying the theory of 

 gravitation with the theory of the Solar System. We should say 

 that there were independent reasons for accepting the Copernican 

 system and the laws of Kepler ; and that though, were the law of 

 gravitation disproved, the pre-existing theory of the Solar System 

 would lack that rational interpretation which the law of gravita- 

 tion gave to it, yet it would remain standing on conclusive evi- 

 dence. 



Mr. Darwin's doctrine of natural selection and the doctrine of 

 organic evolution are, by most people, unhesitatingly supposed to 

 be one and the same thing. Yet between them there is a differ- 

 ence analogous to that between the theory of gravitation and the 

 theory of the Solar System ; and just as the theory of the Solar 



* Inaugural Address to the British Association, 1894. 



