66 THE AGE OF MAMMALS 



The North Polar Theory. — Since the greater land masses of the globe 

 are in the north, we should expect to find a greater number of orders of 

 mammals in the northern hemisphere than in the southern (see p. 68). 

 In 1886 Haacke advanced the extreme theory that all land mammals 

 originated at the North Pole and thence spread southward.' To support 

 this theory it was only necessary to assume land connections between the 

 north polar region and the northern parts of Europe, Asia, and North 

 America, connections between North and South America, between Europe 

 and Africa, between Africa and Madagascar, between Asia and Australia, 

 and between Australia and New Zealand. The climate of the North Pole, 

 according to this theory, was subtropical. In migrating to the south new 

 forms pressed the old ones until the older were forced down to the southern 

 extremities. This would account for the ancient orders of Monotremata 

 and Marsupialia in Australia and for the Marsupialia in southern portions 

 of North America and in South America. The fact that the present conti- 

 nents have as a whole had the same geographic boundaries for long periods 

 of time supports Haacke's theory, which does not presuppose any essential 

 changes in the masses of water and land and renders unnecessary the hy- 

 pothesis of a southern creative center, such as Antarctica. We shall see, 

 however, that there are many facts which can be explained only through the 

 existence of such a great southern land mass. 



Similarly in 1903 Wortman,- calling attention to the proofs of a mild 

 and equable climate growing very gradually cooler as characteristic of the 

 north polar regio;i throughout the early part of the Age of Mammals, 

 assumed the existence of a grand northern common center of evolution and 

 dispersal, both for plants and animals. Such a general southward re- 

 treat of the higher plants and mammals throughout much of the Age of 

 Reptiles and the whole of the Age of Mammals appears to be demonstrated 

 by a succession of waves of migration, utterly unheralded, certainly not 

 coming from the south (that is, from either South America or Africa) and 

 thus as certainly coming from the north, i.e., from a northerly formative 

 evolution area. These southward waves are partly to be ascribed to the 

 lowering of temperature which was inaugurated at the Pole and gradually 

 extended southward. 



Scharff ^ also has favored this theory of a northern creative center of 

 mammalian life. He believes in North Atlantic land connections which 

 must have existed up to very recent geological times between northern 

 Scandinavia and Arctic North America by way of Spitzbergen and Green- 

 land; in fact, in early Pliocene times or perhaps during the Miocene Period 



^ Wilh. Haacke, Der Nordpol als Schopfungscentrum der Landfauna. Biolog. Centralblatt, 

 Vol. 6, 1886-1887, pp. 363-370. 



^ Wortman, Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum, 

 Pt. II, Primates. Amer. Jour. Sci., June, 1903, Vol. 15, pp. 419-436. 



^ Scharff, R., European Animals: Their Geological History and Geographical Dis- 

 tribution, New York, 1907. 



