236 Canon Tristram on the Polar Origin of Life 



XXIII. — The Polar Origin of Life considered in its bearing on 

 the Distribution and Migration of Birds. — Part I. By 

 H. B. Tristram, D.D., F.R.S. 

 The solution of tlie A^arious perplexing problems connected 

 with the classification, distribution, and migration of birds 

 may, as it appears to me, be assisted in no slight degree if 

 we view these problems in the light thrown on them by the 

 theory of the Polar origin of all life. In fact, I can find no 

 problem connected with bird-life which is not more easily 

 explained by this theory than by any other. I hope, therefore, 

 that the readers of ' The Ibis ' will pardon me if I occupy a 

 few pages with a summary of the general question by way of 

 preface. 



However successfully we may classify the distribution of 

 life and sketch the limits of the various regions and areas, 

 yet we cannot find in the most accurate and careful geogra- 

 phical arrangements any clue to the origin or the distribution 

 of bird-life. How is it that while in some families, such as the 

 Thrushes, we find generic identity through the whole v/orld, 

 wliole families, and even orders, are confined to one area 

 and absent from others under identical climatic conditions ? 

 There is certainly nothing in the present distribution of bird- 

 life to explain these phenomena. With so many similarities 

 among so many differences, we cannot assume many original 

 centres of life. We must go back to the original locality of 

 life. It will be granted that life can only have commenced 

 in those parts of the world which were first prepared to main- 

 tain it, and that the earth has been a gradually cooling mass, 

 of which those parts wldch cooled first would be the fittest 

 to maintain life. Now those parts which received the least 

 heat from the sun, and which radiated heat most rapidly 

 into space, must have been the first to cool. These are the 

 Arctic and Antarctic zones. These zones were at one time 

 too hot, and are now too cold for the life which now inhabits 

 the warmer zones, and they must have passed slowly through 

 all the degrees of temj)erature fitted for every form of life 

 which exists or has existed on the earth. I confine myself 

 to the North Polar zone exclusively ; for while, as I shall 



