246 STUDIES IN THE EVOLUTION OF ANIMALS 



that the earhest ancestors of the Horse, such as Phcenacodus, find- 

 ing (perhaps for the first time in the world's history) boundless 

 grassy plains before them, were impelled by a strong desire to run ? 

 The exercise itself must have been enjoyable and invigorating ; 

 besides, the more ground they could cover in a day the greater 

 choice of pasture they would find, while at the same time increased 

 swiftness of foot meant greater safety from flesh-eating enemies.' 



The ' will,' being dependent on some special centre in the brain, 

 cannot possibly be excluded from being a factor, or part of a 

 factor, in natural selection. Probably there is no part of the 

 organism which does not contribute its quota towards the co- 

 operative factorship in natural selection. As to the running being 

 ' enjoyable and invigorating,' one has only to observe a young Foal 

 in a paddock, or the young Eland in its paddock at the Zoological 

 Gardens, to be convinced of the enjoyability of galloping round 

 and round the paddock, as if imaginary devils were running after 

 it. These young animals seem to do it with no other object than 

 that of ' enjoying a gallop ' — a sort of exuberant j'ljz^ de vivre, no 

 doubt impulsed by plenty of nourishing mother's milk. 



The reader who may not have paid much attention to the 

 interesting doctrine of evolution should not suppose that, because 

 the dray Horse is of elephantine dimensions, it could not have 

 descended from an animal as small as a big Dog ; for there have 

 been pigmy Elephants and giant Elephants, pigmy Deer and giant 

 Deer, pigmy Lizards and giant Lizards, pigmy Men and giant Men, 

 and so forth. Large size would appear to be rather a matter of 

 luxuriant feeding which contains all the ingredients of bone, 

 muscle, nerve, etc., and of ease in obtaining it, while small size is 

 the reverse, the structure of the two — large and small — remaining, 

 bone for bone, muscle for muscle, identical, and therefore 

 evidence of derivation from a comrnon stock. Of course a giant 



