102 CAUSES WHICH CHECK 



Chap. XVI. 



Falkland Islands the cattle are breaking up into herds of 

 I different colours ; and those on the higher ground, which are 



generally white, usually breed, as I am informed by Admiral 

 Sulivan, three months earlier than those on the lowlands ; and 

 this would manifestly tend to keep the herds from blending. 



Certain domestic races seem to prefer breeding with their own 

 kind ; and this is a fact of some importance, for it is a step 

 towards that instinctive feeling which helps to keep closely 

 allied species in a state of nature distinct. We have now 

 abundant evidence that, if it were not for this feeling, many 

 more hybrids would be naturally produced than is the case. We 

 have seen in the first chapter that the alco dog of Mexico 

 dislikes dogs of other breeds ; and the hairless dog of Paraguay 

 mixes less readily with the European races, than the latter do 

 with each other. In Germany the female Spitz-dog is said to 

 receive the fox more readily than will other dogs; a female 

 Australian Dingo in England attracted the wild male foxes. 

 But these differences in the sexual instinct and attractive 

 power of the various breeds may be wholly due to their 

 descent from distinct species. In Paraguay the horses have 

 much freedom, and an excellent observer 4 believes that the 

 native horses of the same colour and size prefer associating 

 with each other, and that the horses which have been imported 



from Entre Eios and Banda Oriental into Paraguay likewi 



prefer associating together. In Circassia six sub-races of the 

 horse are known and have received distinct names; and a 

 native proprietor of rank 5 asserts that horses of three of these 

 races, whilst living a free life, almost always refuse to mingle 

 and cross, and will even attack each other. 



It has been observed, in a district stocked with heavy 

 Lincolnshire and light Norfolk sheep, that both kinds, though 

 bred together, when turned out, "in a short time separate 

 to a sheep;" the Lincolnshires drawing off to the rich soil, 

 and the Norfolks to their own dry light soil; and as long as 

 there is plenty of grass, "the two breeds keep themselves as 

 distinct as rooks and pigeons." In this case different habits of 



4 Rengger, ' Saugethiere von Para- and De Quatrefages, in ' Bull. Soc. 



guay,' s. 336. d'Acclimat.,' torn, viii., July, 1861, p- 



5 See a memoir by MM. Lherbette 312. 



