Page six 



EVOLUTION 



May, 1932 



bind It together and the occasional rainstorm torrents cut 

 the loose soil away quickly, exposing the fossil bones. 



Dozens of species have been found, most of them side 

 branches on the family tree of the horse. We must stick to 

 a very few along the direct line of descent. Eohippus, mean- 

 ing the "dawn horse," is the earliest, living during the Eocene 

 Epoch, some fifty million years ago, in our Western states, 

 where the evolution of the horse seems to have occurred. He 

 was somewhat larger than a big cat and had an arched back. 

 However his feet and teeth were not cat-like, but belonged 

 to a browsing, hoofed animal. There were not five toes on 

 a foot, he was too fat along in his evolution for that, but 

 he did have four on each front foot and three on each hind 

 foot. His brain was well developed for his time, a sure sign 

 that he was active and swift, to make up for his smallness. 



From this beginning, we can now trace the changes that 

 came on progressively up through the geological epochs, 

 which for us means up through the geological strata or layers 

 of the earth crust, for the top layers are of course most re- 

 cent. There was an increase in size, but only up to a limit 

 consistent with swiftness. Orohippus, the "mountain horse", 

 and Epihippus, the "upon horse", were just a bit larger than 

 Eohippus. By the Oligocene and Miocene Epochs, about 

 twenty million years ago, Mesohippus and Miohippus were 

 already the size of sheep, and though they had three toes on 

 each foot, the two side toes were getting smaller and much 

 of the weight was carried on the middle toe. Hypohippus 

 came a bit later, as large as a pony, its middle toe looking 

 more like a hoof. And so time and change went on until 

 the horses of today have nearly lost their side toes. I say, 

 "nearly lost" them, for remnants remain as the two splint 

 bones now entirely buried in the flesh. Now and then some 

 horse of today reverts to his ancestors and is born with extra 

 toes on his feet. Julius Caesar owned such a horse and 

 more are on record. 



You may talk about your old families, but none can ride 

 the high horse on the horse; he has a pedigree that stretches 

 back at least fifty million years. But properly, like other 

 folks with ancestors, he has little reason to take pride, for 

 he had nothing to do with it himself. After all, we are all 



Smu/l 4-Tord UorifS' \STvalI i Fofi \ Lar^t i-Totd \ Lar^t: l-Toed 



Orchippui- 



Epihtppui 



Mnohtppui 

 AjicmUli'ium 

 Mype/iipptii 

 ParaJiippus 

 Mtr^entppui 

 Proto/lippui 



Pttonippu 



H'ppidiun 

 Onohippidiu^ - - — (S^outfi America 



Hippu n i: 



'(Europe aii-f D/orlri America)- ^ 

 ^Nartlt America. Asia and\£urope)-\ 



(NcrU AmeLct) ' 



(Ka,,), America.)- H -•*-«|B 



. . (No-rf America)- -I-- - ]'* 



- - (A^m/ri America)- '- - -,- - 



■ lS)iatli America f V ■ 



-( hotlh America .Ana. Eurbpc and A/aiM A^nca)- > 



{A'ef:r> 1,11.1 Sai^rf' An iiiia |/i]/fl. Furope i^iid Af>, 



Ccurlcsy American Muieum of Natural History 

 Evolution of Hind Foot of Horse 

 Eohippus, Mesohippus, Miohippus, Merichippus, Hipparion, Equus. 



Courtesy American Museum of Natural History 

 Geological and Geographical range of ancestors of horse. Black lines 

 show life span of each genus. Dots, show line of descent. 



creatures of conditions, made by our environments which 

 make demands that we must needs meet, or die out. If our 

 variations change us in the right directions, we survive, if 

 not, our careers end. A change of climate made the horse. 



When Eohippus made the start, our Western country was 

 low and swampy, just emerged from the sea, for the earth 

 crust here was rising. The climate was moist and the country 

 forest-covered. In these woods, Eohippus hid, alert and 

 quick on the get-away when he was discovered. His coat 

 may have been striped like a zebras to help him hide. His 

 wide, three- and four-toed feet kept him from sinking into 

 the soft ground. He browsed on leaves, which are soft, so 

 his teeth were a browser's teeth, more like those of a tapir 

 than a modern horse. 



But not only were the swampy forest lands rising; a 

 mountain range was being uplifted to the West, cutting oil 

 the moist winds of the Pacific, causing a dry climate which 

 discouraged the forests. Slowly the woodlands gave way to 

 the grasslands, and the horse found himself out in the open, 

 exposed to many dangers, among them a shortage of leafy 

 food. To survive in this environment, he had to acquire speed 

 for escape and for rapid ranging for his food supply, and 

 had to develop teeth for grinding grasses. The horse perforce 

 became a grazing animal instead of a browser. His teeth dis- 

 close that conclusively. Up front they became sharp for 

 cutting. Then came a toothless space, where we place our 

 bridle bits. And way back, where the jaws have a strong 

 leverage, came the grinders. They became strong, fitted for 

 tough, hard food. The grinders have rough surfaces of com- 

 plex pattern, due to unequal wearing down of the twisty 

 alternating edges of glassy-hard enamel and the soft dentine 

 and cement between. In the early horse, the surface patterns 

 were simple, but as they evolved, the patterns became complex 

 and more horse-like in the modern sense. Also they became 

 longer in root and crown, permitting them, after their ori- 

 ginal growth to maturity, to move instead of grow outward 

 for many years as their surfaces wore down. Altogether, the 

 teeth became fit for cutting and grinding great quantities of 



