904 LIFE : OUTLINES OF GENERAL BIOLOGY 



Furthermore, coming to what here mainly concerns us, they lay 

 great stress on the bearing of these great periods of cold cUmate — 

 and indeed also of minor ones, especially that of the early Eocene — 

 upon the progression of organic life. Says our first author, Prof. 

 Coleman of Toronto : "The process of elimination of the weaker, less 

 adaptable, forms during Ice Ages seems one of the most effective 

 ways in which new and more viable species arise ; so that the ever- 

 multiplying plants and animals have their ranks thinned, leaving 

 room for the more progressive species. The hastening and intensi- 

 fying of the process of evolution in glacial periods is undoubtedly 

 one of the most important ways of developing the life of the world, 

 and should receive the special attention of biologists." 



In his Climate through the Ages (1926), Mr. C. Brooks compares Ice 

 Ages in the climatic history of our planet to cyclones in a tropical 

 island. As hitherto, but now more fully, he reasonably assumes the 

 character and past distribution of characteristic vegetation as indica- 

 tive of prevalent climates at given places and times; so from 

 many facts, like the existence of Sequoia gigantea ("Wellingtonia") 

 in Tertiary Greenland, we see that the mean sea-level temperature 

 must have been everywhere higher than at present ; whence warmer 

 tropics, sub-tropical climate in our temperate zone, temperate polar 

 areas, and practically no polar climate as at present. In these long 

 "periods of normal climate", the rains in what are now temperate 

 regions would thus be less frequent, but of sub- tropical character, with 

 rapid evaporation and dry periods between. His conception is of long 

 normal periods, modified by abnormal yet cyclically recurrent glacial 

 periods ; and it thus suggestively combines, upon our modern spiral, 

 the values of uniformitarian geology with those of more catastrophic 

 views. And if such alternations in the genesis of our physical world 

 are cyclic, and thus fall into the rhythm of one great metastrophe, 

 may not our difficulties in the general understanding of organic 

 evolution be abated by again thinking of its changes as associatedly 

 metastrophic ? For thus we can better imderstand the stabilities 

 and permanences of life's history, yet also its striking disappear- 

 ances; its innovations also; and these from "big lifts" to manifold 

 differentiation of species in detail — all becoming more intelligible. 

 Such ideas have indeed been long coming up, in fact, since the oldest 

 doctrines of "creative periods", yet it is much if we are thus reach- 

 ing a clearer general conception of the world process, and this with 

 increasing light upon its particulars. 



Dr. Newbigin ably condenses and sometimes develops the con- 

 ceptions of both our authors, reviewing the main ascents of life and 

 the increase of diversity of type and species, in association with 

 these cyclic changes of world configuration and climate. The develop- 

 ment of diversity of type seems associated with an increase in the 

 area occupied by terrestrial organisms. Thus in warm conditions 



