318 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1925 



Tropical cj'clones have also played a part in the distribution of 

 peoples over the Pacific. Legendar}^ accounts indicate that a num- 

 ber of island groups were discovered by occupants of boats that had 

 been blown out of their course by storms. The discovery of New 

 Zealand by Polynesians en route from Samoa to the Cook Islands is 

 a specific illustration.^^ 



MAN AS AN AGENCY OF DISPERSAL 



The great importance of man in distributing plants and animals 

 of economic importance and, incidentally and inadvertently, of 

 numerous smaller species concealed in the soil or bark or on leaves has 

 been emphasized by several scientists.^*^ 



GEOLOGIC CHANGES 



The dispersal of life from island to island over the Pacific has 

 been accomplished slowly. Undoubtedly, during the geologic ages, 

 there have been geologic changes that have been significant. For 

 example, it is known that long ago there was more than once a 

 strait where the continuous Central America now is. Conceivably at 

 such times the drift induced by the trade winds, and which is now 

 diverted northward in the Atlantic to form the Gulf Stream, may 

 have continued westward carrjnng with it some of the seed plants 

 and animals of the islands situated where Central America now is." 



Likewise, any tropical cyclones that occurred then in the Carib' 

 bean region would have been more likely than now to sweep west- 

 ward far into the Pacific, for the atmospheric pressure conditions 

 prevailing over the land, especially mountainous land, seem often to 

 divert tropical cyclones. 



Likewise, it is known that Australia was formerly connected with 

 Asia by way of the East Indies and New Caledonia. At such times, 

 it is probable that the normal ocean currents were distinctly different 

 from the present. While now part of the equatorial current finds its 

 way westward between the islands and enters the Indian Ocean, for- 

 merly the continuous land necessarily diverted the warm equatorial 

 current into higher latitudes. 



Another change during the geologic past, which is much jnore 

 frequently mentioned, is the lowering of tlie sea level during the 

 accumulation of the continental glaciers of the several ice ages. It 



"^ Best, KIstoii, " Polynesian navigators, their exploration and settlement of the Pacific." 

 Geographical Review, vol. r>, pp. 169-181;, 1018. 



" For exanTple, by Mayor, Alfred G., and Safford, W. E., in Proceeding's First Pnu-Paciflc 

 Scientific Conference, vol. 1, pp. 15, 147, 183-187, and by P.est Elston, loc. cit. Safford 

 lias mndo ospocial .study of the cultivated plants of Polynesia, loc. cit., pp. 183-187. See 

 also Guppy, II. B., " Observations of a Naturalist in tho Pacific," vol. 2, on " The dis- 

 tribution of plants and animals," Loudon, 1908. 



>' Brown, F. B. II., loc. cit. 



