MIGRATIONS OF RACES OF MEN CONSIDERED HISTORICALLY. 583 



third is the colonization of tlie temperate parts of the North American 

 coast by the English, French, ami Dntch in the seventeenth century; 

 the fourth is the immense outtlow from Kurope, not only to America 

 but also to Australasia, and — in a much smaller degree — to South Africa, 

 auovertlowmainlydueto the progress of physical science; firstly, in intro- 

 ducing the use of steam for ocean voyages, and, secondly, in so acceler- 

 ating the growth of population iu Europe that the impulse toward less 

 crowded lands became stronger than ever before. The scale of this 

 outtlow of the last seventy years has been far larger than that of any 

 previous time, and has indeed become possible only because ocean 

 transit is now so swift, safe, and cheap. The export of Chinese to 

 America, and of Indian coolies to and fro in the tropics, is in like man- 

 ner attributable to the cheapness with which they can now be carried 

 for long distances, as well as (in the case of the coolies) to the increased 

 demand for tropical products which the growth of population and of 

 wealth iu the north temperate zone has created. 



v. — THE CORRELATIONS OF MIGRATION. 



Among the many questions suggested by the facts we have noted, 

 I will advert to two or three only. 



One of these bears on the analogy between the migrations of man- 

 kind and those of other animals and of plants. If the majority of our 

 geologists are right iu holding that man existed in those very remote 

 times in which great changes of climate were still taking place, the 

 analogy must then have been close. Races of men may, in paheolithic 

 times, have moved northward or southward, according to the recession 

 or advance of the great ice sheet that once covered the northern part 

 of the north temperate zone, just as we know that animals moved, and 

 just as we find that certain species of i)lants have, iu our latitude, 

 sometimes occupied the low country, 'and sometimes retired to sub- 

 arctic regions or ascended to the tops of the loftiest mountains. It 

 has been lately maintained that the Eskimo of Arctic America are 

 the descendants of the Cave men of Britain and France, driven north 

 many thousands of years ago by the growing mildness of the climate. 

 We know that changes in the level of the sea have produced revolu- 

 tions in the fauiia and flora of countries, not only by affecting the 

 course of ocean currents, and tliereby the climate, but also by bringing^ 

 when lands formerly separated l)ecame parts of the same continent, 

 species from one land to another, where the incomers overpowered or 

 expelled the old inhabitants, or became, under new conditions and 

 through the struggle between competing species, themselves so modi- 

 fied as to pass into new forms. If man existed at a time so distant as 

 that wherein Bering Straits and the North Sea and i^art of the Medi- 

 terranean were dry land, we may conjecture, from the influence of these 

 physical changes upon the animal and vegetable world, what their 



