98 EVOLUTION THE RESULT OF CHEMICAL FORCES. 



found in the Eocene or lowest Tertiaries in our western terri- 

 tories. Professors Marsh and Leidy have found in later strata 

 the remains of other equine animals, with a gradually lessening 

 number of toes, increasing size and horse-like appearance, and 

 consolidation of the double leg-bones, forming connecting links 

 through at least six hippoid forms up to the present genus, Equus. 



The toes are got rid of in these successive forms by being 

 withdrawn upwards, at first just clearing the ground, then drawn 

 up into what are called dew-claws, then into splints on the meta- 

 carpus, then vanishing altogether. They are always removed in 

 a regular prescribed order, in this as well as in every other case 

 of the elimination of these members ; first the big toe, number 

 one ; then the little toe, number five ; then number four, or 

 numbers two and four together, leaving two as in the ox, or only 

 the middle one as in the horse. This regular order in the devel- 

 opment of the ungulates precludes all possibility of chance being 

 concerned in the operation. Chance makes no selections. 



The fundamental doctrine of natural selection as set forth by 

 Darwin is the perpetuation through inheritance of slight advan- 

 tageous changes happening to any organism.* These must how- 

 ever be of sufficient advantage to enable the possessors of them, 

 by reason thereof, to run out and supercede all the animals not 

 possessing them ; for otherwise the peculiarities would certainly 

 be lost or merged by interbreeding. Indeed it is one of the 

 great mysteries of natural selection in the wild state, how any 

 slight variation happening to one individual is preserved for any 

 length of time from being merged in the common characteristics 

 of the race. However let us suppose that some one Eohippus 

 of the ancient eras had been favored with a slight elevation from 

 the ground of the fifth hoof -toe of each fore foot, and that this 

 peculiarity had been successfully transmitted to a line of descen- 

 dents. Three toes then touched the ground when running, 

 but the little toe hung somewhat loose and failed to make a 

 track. Now can it possibly be imagined that there was advan- 



* "As natural selection acts solely by accumulating slight, successive, favor- 

 able variations, it can produce no great or sudden modifications; it can 

 act only by very short and slow steps." Origin of Species, page 409. 



