CONGRUITY OF THE EVIDENCE 309 



we happen to live during one of those great phases in the earth's 

 history in which an aberrant type, having within itself vast and 

 altogether peculiar capacities for improvement, has, on account of 

 the high development of these capacities, overrun the earth. 

 Those mysterious powers and natural tendencies, which formerly 

 sufficed to produce the great fish-like lizards and crocodiles, and 

 which, among birds, have expended themselves in the perfection 

 of an elaborate respiratory system and in the production of related 

 changes in their integumentary system and organs of locomotion, 

 seem, in the case of Man and of the race from which he has been 

 developed, to have been expended in the production of much less 

 obvious external changes, although these have been accompanied 

 by the most important internal changes, leading to the gradual 

 elaboration of the Brain, or principal Organ of Mind. 



An increased development of the brain, however initiated, and 

 even when it gave to primeval Man mental powers very slightly 

 in excess of those of the man-like apes, would, after a time, as 

 Wallace has ably shown,' almost inevitably tend to give him that 

 power over natural products and forces which in the course of 

 ages has enabled him to make these forces subservient to his own 

 wants in a gradually increasing degree. 



The facts and views brought forward in the present work will 

 be found to have a very important bearing upon another problem 

 of great speculative interest, namely, the question of the time 

 needful for the Evolution of all the Forms of Life that have ever 

 appeared upon the Earth, and should not be without influence in 

 bringing much more into harmony, than is at present the case, 

 the views entertained by physicists, geologists, and biologists 

 respectively, as to the probable duration of life upon our globe. 

 The actual age of the globe, and also the time that must be 

 supposed' to have elapsed since the first appearance of living 

 things upon its surface, has given rise to a considerable amount of 

 discussion since Sir William Thomson (now Lord Kelvin) in 1862 

 first endeavoured to show in a paper ^ on " The Secular Cooling of 

 the Earth," that great limitations had to be put upon the enormous 

 demands for time made by Sir Chas. Lyell and his immediate 

 followers in accounting for all the series of changes on the surface 

 of the earth that come within the ken of the geologist. 

 The very positive expression of Lord Kelvin's views in this 



' " Contributions to the Tlieory of Natural Selection," 1870, p. 319. 

 2 "Trans, of Roy. Soc. Edin.," vol. xxiii., p. 157. 



