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however, who live on the rivers, and use them as highways, have names for them all; but to the agricultural Indians and Mestizos of the interior, they are but reservoirs of water, crossed at distant points by their roads, and everywhere amongst them. I found the greatest ignorance to prevail as to the connection of the different streams, and of their outflow to the ocean. All the streams about Olama flow eastward, and join together to form the Rio Grande, that reaches the Atlantic about midway betwen Blewfields and the river Wanks; it is very incorrectly marked on all the maps of Nicaragua that I have seen. The Caribs from the lower parts of the river occaSionally come up in their canoes to Olama, and bring with them common guns and iron pots that they have obtained from the mahogany cutters at the mouth of the river. These they barter for dogs. I could not ascertain what they wanted with the dogs, but both at this place and at Matagalpa I was told of the great value the Caribs put on them. Although the people of Olama expressed great surprise that the “Caritos,” as they call the river Indians, should take so much trouble to obtain dogs, they had not had the curiosity to ask them what they wanted them for. Some people near the river have even commenced to rear dogs, to supply the demand. The Caribs had a special liking for black ones, and did not value those of any other colour so much. They would barter a gun or a large iron pot for a single'dog, if it was of the right colour. The common dogs of Central America are a mongrel breed—not differing, I believe, from those of Europe. There are usually a number of curs about the Indian

Ch. XI.] THE HAIRLESS DOG. 205

houses that run out barking at a stranger, but seldom bite. The hairless dogs, mentioned by Humboldt, as being abundant in Peru,” are not common in Central America, but there are a few to be met with. At Colon I saw several. They are of a shining dark colour, and are quite without hair, excepting a little on the face and on the top of the tail. Both in Peru and Mexico this variety was found by the Spanish conquerors. It would be interesting to have these dogs compared with the hairless dogs of China, which Humboldt says have certainly been extremely common since very early times. Perhaps another link might be added to the broken chain of evidence that connects the peoples of the two countries. A large naked dog-like animal is figured by Clavigero as one of the indigenous animals of Mexico. It was called Xoloitzcuintli by the Mexicans; and Humboldt considers it was distinct from the hairless dog, and was a large dog-like wolf. Its name does not support this view; Xoloitzcuinth literally means “a servant dog,” from “Yolots,” a slave or servant, and it2cuintli, a dog; and we find the word Xolotl in Hueallots, the Aztec name of the common turkey, which was domesticated by them, and largely used as food. I am led to believe from this, that Xolotl was applied to any animal that lived in the house or was domesticated, and that the Xoloitzcuintli was merely a large variety of the hairless dog. Clavi. gero's description of it would fit the hairless dog of the present day very well, excepting the size ; he says, it was four feet long, totally naked, excepting a few stiff hairs * “Aspects of Nature,” vol. i. p. 109.

on its snout, and ash coloured, spotted with black and tawny. Tschudi makes two races of indigenous dogs in tropical America. 1. The Canis caraibicus (Lesson), without hair, and which does not bark. 2. The Canis ingae (Tschudi), the common hairy dog, which has pointed nose and ears, and barks.” The small eatable dog of the Mexicans was called by them Techichi ; and Humboldt derives the name from Tets, a stone, and says that it means “a dumb dog,” but this appears rather a forced derivation. Chichi is Aztec for “to suck; ” and it seems to me more probable that the little dogs they eat, and which are spoken of by the Spaniards as making very tender and delicate food, were the puppies of the Xoloitscuintli, and that Techichi meant “a sucker.” Whether the hairless dog was or was not the Techichi of which the Mexicans made such savoury dishes is an open question, but there can be no doubt that the former was found in tropical America by the Spanish conquerors, and that it has survived to the present time, with little or no change. That it should not have intermixed with the common haired variety, and lost its distinctive characters, is very remarkable. It has not been artificially preserved, for instead of being looked on with favour by the Indians, Humboldt states that in |Peru, where it is abundant, it is despised and ill-treated. Under such circumstances, the variety can only have been preserved through not interbreeding with the common form, either from a dislike to such unions, or by some amount of sterility when they are formed.

* J. J. von Tschudi, quoted by Humboldt, “Aspects of Nature,” English edition, vol. i. p. 111.

Ch. XI.] NATURAL AND ARTIFICIAL SELECTION. 207

This is, I think, in favour of the inference that the variety has been produced by natural and not by artificial selection, for diminished fertility is seldom or never acquired between artificial varieties. Man isolates varieties, and breeds from them, and continuing to separate those that vary in the direction he wishes to follow, a very great difference is, in a comparatively short time, produced. But these artificial varieties, though often more different from each other than some natural species, readily interbreed, and if left to themselves, rapidly revert to a common type. In natural selection there is a great and fundamental difference. The varieties that arise can seldom be separated from the parent form and from other varieties, until they vary also in the elements of reproduction. Thousands of varieties probably revert to the parent type, but if at last one is produced that breeds only with its own form, we can easily see how a new species might be segregated. As long as varieties interbreed together and with the parent form, it does not seem possible that a new species could be formed by natural selection, excepting in cases of geographical isolation. All the individuals might vary in some one direction, but they could not split up into distinct species whilst they occupied the same area and interbred without difficulty. before a variety can become permanent, it must be either separated from the others, or have acquired some disinclination or inability to interbreed with them. As long as they interbreed together, the possible divergence is kept within narrow limits, but whenever a variety is produced, the individuals of which have a partiality for interbreeding, and some amount of sterility when

crossed with another form, the tie that bound it to the central stock is loosened, and the foundation is laid for the formation of a new species. Further divergence would be unchecked, or only slightly checked, and the elements of reproduction having begun to vary, would probably continue to diverge from the parent form, for Darwin has shown that any organ in which a species has begun to vary, is liable to further change in the same direction.* Thus one of the best tests of the specific difference of two allied forms living together, is their sterility when crossed, and nearly allied species Separated by geographical barriers are more likely to interbreed than those inhabiting the same area. Artificial selection is more rapid in its results, but less stable than that of nature, because the barriers that man raises to prevent intermingling of varieties are temporary and partial, whilst that which nature fixes when sterility arises is permanent and complete. For these reasons I think that the fact that the hairless dog of tropical America has not interbred with the common form, and regained its hairy coat, is in favour of the inference that the variety has been produced by natural and not by artificial selection. By this I do not mean that it has arisen as a wild variety, for it is probable that its domestication was an important element amongst the causes that led to its formation, but that it has not been produced by man selecting the individuals to breed from that had the least covering of hairs. I cannot agree with Some eminent naturalists that the loss of a hairy covering would always be disad

* See “Animals and Plants under Domestication,” vol. ii. p. 241.

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