888 LIFE : OUTLINES OF GENERAL BIOLOGY 



feathered bird, the joy of creation". But we must think not of 

 transformation, but of origination and divergence. 



EFFECT OF THE ICE-AGES 



In the discontent of very severe winters people sometimes say 

 that they are "feehng the cold badly"; and that is the time for 

 a sympathetic consideration of the problem of the Ice Ages. It 

 is only a few thousand years since the great glaciers finally dis- 

 appeared from Britain, making it possible for man to return to his 

 old haunts, or, in the case of Scotland, to explore new territory. 

 For the first-comers to Scotland, about 10,000 years ago, were, so 

 far as is certain, post-glacial Neolithic hunters and fishers, though 

 there is evidence of Paleolithic forerunners farther south. 



Since great ice-sheets, sometimes 3,000 feet thick, had covered 

 the whole of Scotland and most of England during the successive 

 Ice Ages of the Pleistocene Period, the old fauna and flora had been 

 swept away, except such as found refuge along a non-glaciated strip 

 which we call nowadays the South of England. Not only was there 

 an extinction of grandiose creatures like rhinoceros and hippopota- 

 mus, mammoth and cave lion; there was a wiping out of practi- 

 cally all the fauna except in ice-free regions, except during the 

 four or so interglacial periods when mild conditions prevailed 

 for cycles of years and allowed adventurous colonists to return 

 for a while. 



Some geologists think that we are in an interglacial period even 

 now; and to this the cold ocean depths — now generally interpreted 

 as a survival of the recent ice-age — might readily again contribute, 

 if aided by slight increase of the down currents from Arctic and 

 Antarctic. For we seldom realise how but a few degrees of lowered 

 average annual temperature are needed. But the point is that, after 

 the ice-sheets disappeared and left the land clear, there was a 

 faunistic re-colonisation of Britain from the Continent. For Britain 

 was still just an outlying corner of Europe. Across grassy lowlands, 

 where the North Sea and the English Channel now lie, there came 

 the reindeer and the elk, the bear and the wolf, the lemming and 

 the beaver, besides all the mammals that are still with us. On the 

 heels of these animals, and many of humbler rank, came Neolithic 

 Man, bringing domesticated animals with him. Then a depression 

 of land occurred, Britain became an island, and the door was shut 

 to any further colonisation on the part of terrestrial animals. When 

 we think of the terrible elimination that was effected by the Great 

 Ice Age glaciers — there is no desert like ice ! — we can imagine what 

 a faunistically poor country Britain would have been, as regards 

 land animals, if it had been insulated before these Ages of Horror, 



