392 



The Possible Ancestors of the Horses living under 

 Domestication. 

 By J. C. Ewart, M.D., F.R.S., University of Edinburgh.' 



(Received May 15,— Read June 24, 1909.) 



(Abstract.) 



During the later part of the Nineteenth Century it was generally taken 

 for granted — (1) that " the seven or eight species of Equidae now existing are 

 all descended from an ancestor of a dun colour more or less striped ";* (2) that 

 the common ancestor of the living horses, asses, and zebras was connected 

 by a single line of descent with the four-toed " fossil " horses of the Eocene 

 period ; (3) that the domestic horses are descended from a Pleistocene species 

 characterised by large molars with a long anterior internal pillar, a large, 

 heavy head, and coarse limbs ; (4) that in various parts of Europe and Asia 

 domestic races increased in size and were improved in make, speed, and 

 disposition as a result of artificial selection and favourable surroundings. 



On the Continent it seems to be still generally assumed that the domestic 

 breeds have descended from a single species,! but in England and America 

 many naturalists now believe — (1) that domestic horses have sprung from 

 several wild species, connected by several lines of descent with three-hoofed 

 species of the Miocene period ; and (2) that while some of the wild ancestors 

 were adapted for living in the vicinity of forests and upland valleys, others 

 were adapted for a steppe, plateau, or desert life. 



Of possible ancestors of the domestic breeds, the following may be 

 mentioned : — Equus sivalensis, E. stenonis, E. gracilis (Owen's Asinus fossilis), 

 E. namadicus, E. fossilis, and E. robustus. These species mainly differ in the 

 teeth, size and deflection of the face, and in the bones of the limbs. In the 

 first three species, the grinding surface of the anterior internal pillar (a fold 

 of enamel on the inner surface of the cheek teeth) of the premolars and first 

 molar is short, in the last premolar, pm. 4, it may only be one-third the 

 length of the crown; in the second three species, the anterior internal 

 pillar is long — at least half the anteroposterior length of the crown. 



One of the ancestral types (E. robustus) was broad browed and had a short 

 face, almost in a line with the cranium ; another (E. sivalensis), also broad 

 * Darwin, 'Animals and Plants,' vol. 2, p. 17. 



t The latest suggestion is that domestic horses are the descendants of Equus fossilis, 

 Riitimeyer, a Pleistocene species closely allied to the wild horse of Mongolia — 



E. przewalskii. 



