MR. M1VART AND MR. DARWIN. 283 



"Sir William Thompson has lately advanced argu- 

 ments from three distinct lines of inquiry agreeing in 

 one approximate result. The three lines of inquiry are 

 (i) the action of the tides upon the earth's rotation ; (2) 

 the probable length of time during which the sun has 

 illuminated this planet ; and (3) the temperature of the 

 interior of the earth. The result arrived at by these 

 investigations is a conclusion that the existing state of 

 things on the earth, life on the earth, all geological history 

 showing continuity of life, must be limited within some 

 such period of past time as one hundred million years. 

 The first question which suggests itself, supposing Sir W. 

 Thompson's views to be correct, is : Has this period been 

 anything like enough for the evolution of all organic 

 forms by 'natural selection' ? The second is : Has the 

 period been anything like enough for the deposition of 

 the strata which must have been deposited if all organic 

 forms have been evolved by minute steps, according to 

 the Darwinian theory ? " (" Genesis of Species," p. 154). 



Mr. Mivart then quotes from Mr. Murphy whose 

 work I have not seen the following passage : 



" Darwin justly mentions the greyhound as being 

 equal to any natural species in the perfect co-ordination 

 of its parts, ' all adapted for extreme fleetness and for 

 running down weak prey.' Yet it is an artificial 

 species (and not physiologically a species at all) formed 

 by a long-continued selection under domestication ; and 

 there is no reason to suppose that any of the variations 

 which have been selected to form it have been other 

 than gradual and almost imperceptible. Suppose that 

 it has taken five hundred years to form the greyhound 



