Dr. W. T. Blanford — Age of the Himalayas. 165 



picticnndata as peculiar genera. But omitting all doubtful forms, 

 and taking no account of varieties or subgenerio types, it will be 

 found that in the preceding list of 43 species, 27 are peculiar, and 

 of 26 genera, 4. So far as I am aware there is no other instance 

 in the world of a continental area of the size of Tibet that contains 

 an equally peculiar Mammalian fauna. It should also be remarked 

 that by far the largest proportion of species ranging beyond Tibet 

 is exhibited by the Carnivora, which are great wanderers, and that 

 among the Ungulates, wide-ranging forms as a rule, only four species 

 out of nine (omitting Budorcas and Cervus nffinis) are found else- 

 where, two at least of these four being represented in Tibet by well- 

 marked varieties. Of the Rodents, 16 in number, only one species is 

 known to range into other parts of Asia. The solitary Oriental 

 (Indian or Indo-Chinese) species in the whole list is Gt/on Deccanensis, 

 the so-called Wild Dog of India, which, strange to say, does occur 

 on the Tibet plateau, whilst the Siberian representative of the genus, 

 C alpinus, is absent. In other respects the affinities of the Tibetan 

 mammal fauna are distinctly Palcsarctic. 



I have said that so far as I am aware no other continental area of 

 the same size with an equally distinct fauna is known. For similar 

 examples of specific and generic distinction we must look to islands. 

 The diffei-ence, for instance, between the Mammalian fauna of 

 Madagascar and that of Africa is far greater than that between 

 the Mammals of the Tibetan plateau and those of other parts of 

 Central and Northern Asia ; whilst the differences between such 

 Malay islands as Sumatra, Java and Borneo, or between any of them 

 and the Malay Peninsula, is much less. On the whole the greatest 

 similarity to the Mammalian relations of Tibet is presented by the 

 island of Celebes, provided the Australian affinities of a minority 

 of the Celebean Mammals be neglected.^ 



The view is, I believe, generally accepted that the difference 

 of the fauna of any island from that of the nearest land is due to 

 isolation of greater or less duration ; and if the theory of evolution 

 is accepted, and it is admitted that the different forms of Mammals, 

 whether nearly or distantly related, have a common origin, it is a 

 reasonable conclusion that the amount of difference between the 

 forms inhabiting two neighbouring but separated areas has a distinct 

 relation to the time that has elapsed since the areas were isolated 

 from each other ; those tracts in which there is a generic difference 

 having been longer separated than those in which the distinction 

 is only specific. 



Thus it is probable that the separation of Borneo, Sumatra and 

 Java, from each other and from the Malay Peninsula, is not older 

 than Pleistocene or Newer Pliocene, the isolation of Java being of 

 somewhat earlier date than that of the other two islands. The 

 separation of Celebes from the rest of the Oriental region must be 

 more ancient, and in " Island Life " Wallace suggests that it may 

 date back to Miocene times. Bearing in mind that the isolation of 



' They are probably of later irLtroduction than the Mammals with Oriental 

 affinities. 



