It is a significant circumstance when we come to consider the probable origin of the dog, that there are indications of his domestication at such early periods by so many peoples in different parts of the world. As we have seen, dogs were more or less subjugated and tamed by primitive man, by the Assyrians, Egyptians, Phoenicians, Greeks, and Romans, as also by the ancient barbaric tribes of the western hemisphere. The important question now arises: Had all these dogs a common origin in a definite parent stock, or did they spring from separate and unrelated parents? Half a century ago it was believed that all the evidence which could be brought to bear upon the problem pointed to an independent origin of the dog. Youatt, writing in 1845, argued that "this power of tracing back the dog to the very earliest periods of history, and the fact that he then seemed to be as sagacious, as faithful, and as valuable as at the present day, strongly favours the opinion that he was descended from no inferior and comparatively worthless animal; and that he was not the progeny of the wolf, the jackal, or the fox, but was originally created, somewhat as we now find him, the associate and friend of man." When Youatt wrote, most people believed that the world was only six thousand years old, and that species were originally created and absolutely unchangeable. Lyell's discoveries in geology, however, overthrew the argument of the earth's chronology and of the antiquity of man, and Darwin's theory of evolution entirely transformed the accepted beliefs concerning the origin of species and the supposed invariability of animal types. The general superficial resemblance between the fox and many of our dogs, might well excuse the belief in a relationship. Gamekeepers are often very positive that a cross can be obtained between a dog fox and a terrier bitch; but cases in which this connection is alleged must be accepted with extreme caution. The late Mr. A. D. Bartlett, who was for years the superintendent of the Zoological Gardens in London, studied this question with minute care, and as a result of experiments and observations he positively affirmed that he had never met with one well-authenticated instance of a hybrid dog and fox. Mr. Bartlett's conclusions are incontestable. However much in appearance the supposed dog-fox may resemble the fox, there are certain opposing characteristics and structural differences which entirely dismiss the theory of relationship.