To take another example, it has been proved by geologists that the present wild horse (Equus Przewalski) has slowly been evolved during the later parts of the Tertiary and the Quaternary period, but that during this succession of ages its ancestors were not confined to some given, limited area of the globe. They wandered over both the Old and New World, returning, in all probability, after a time to the pastures which they had, in the course of their migrations, formerly left.(34) Consequently, if we do not find now, in Asia, all the intermediate links between the present wild horse and its Asiatic Post-Tertiary ancestors, this does not mean at all that the intermediate links have been exterminated. No such extermination has ever taken place. No exceptional mortality may even have occurred among the ancestral species: the individuals which belonged to intermediate varieties and species have died in the usual course of events--often amidst plentiful food, and their remains were buried all over the globe. In short, if we carefully consider this matter, and, carefully re-read what Darwin himself wrote upon this subject, we see that if the word "extermination" be used at all in connection with transitional varieties, it must be used in its metaphoric sense. As to "competition," this expression, too, is continually used by Darwin (see, for instance, the paragraph "On Extinction") as an image, or as a way-of-speaking, rather than with the intention of conveying the idea of a real competition between two portions of the same species for the means of existence. At any rate, the absence of intermediate forms is no argument in favour of it. In reality, the chief argument in favour of a keen competition for the means of existence continually going on within every animal species is--to use Professor Geddes' expression--the "arithmetical argument" borrowed from Malthus.