RECENT EMIGRATION iCg 



or a return to more suitable conditions permitted an 

 extension of area. The one dominant ruling passion of 

 Life in its endless varying forms is to increase and to 

 spread. That such an impulse to spread still rules 

 supreme, though less acutely than in the more remote 

 Post-Glacial ages, less palpable because the conditions 

 are so much less strongly marked, less dominant than 

 during those chaotic eras — is a fact as incontrovertible 

 as the very existence of Life itself. That the world is 

 never in a state of absolute rest is another truism 

 admitted by every scientific observer of nature. These 

 two facts imply that the Emigration of Life is still in 

 progress ; that birds, animals, insects, and plants still 

 continue to colonize new areas, or attempt to do so, 

 with their surplus individuals or excessive and increasing 

 population. This colonizing movement is of a much 

 more restricted nature than it was immediately after the 

 Glacial Epoch, due to the greater difficulties in the way 

 of successful extension of range, owing to the much 

 greater abundance of competing forms, and the much 

 less extensive areas supplying the necessary conditions 

 favourable for such emigration. We can readily under- 

 stand the impetus given to Emigration by the passing 

 away of the Ice Age, and the opening out of half a 

 hemisphere to the remnants of the species dwelling in 

 the southern areas, vast numbers of which were perhaps 

 dwelling therein at a disadvantage, and under the least 

 favourable conditions for maintaining themselves and 

 for successful increase. We can also understand after 

 the great exodus north was nearly spent, how the 

 stimulus to Emigration would become much less acute, 

 and would therefore progress more slowly, until we can 



