A corallary following from these facts is of the utmost importance. If a wave of population migrated south into a milder climate where living was easier, and the stupid man could survive and raise children as well as his brighter brothers and cousins, then there was a cessation of the natural selection of the brainiest and the further evolution of higher men. Evolution requires a ruthless slaughter of those of a certain type, and if there is no slaughter there is no evolution of the opposite type. Hence, migration south forever stopped evolution of brains, and these races are in the same mental stage as when they left the cradle of the race. The longer a race stayed in the struggle of wits in the north the brainier it became. Hence, the further north we go from the tropics into Europe the larger are the average brains. The smaller the brain of a race or tribe, the earlier must its ancestors have left the northern brain factory. Each succeeding wave of emigration to the south was brainier than the last and overran the country, enslaving earlier arrivals or exterminating them.
The races which stayed north after the glacial period, found that they could spread further north still and they followed the retreating ice-cap, so that at the present time, the races which have been longest under this selection of the brainiest - the Baltic or Aryan - are occupying the identical ground which was covered by ice when their ancestors were first evolved into men further south. They did not arrive in Scandinavia until quite late, by which time they had created quite a degree of civilization called the neolithic. It is a curious fact, that the extent of the great Scandinavian glacier whose southern edge was in Northern France and Germany, and covered the British Isles, is the very area now holding the type of man who rules the world - the Aryan - the man longest under brain evolution and the survivor of the awful destruction of the stupid. It holds an advantage purchased by the lives of millions of blood relatives.
The severity of the environment evidently ceased in Asia a very long time before it did in Europe, so that civilization began and brain evolution stopped ages ago, and has not progressed since. Asiatics, as a rule, being of less average brain and less intelligence, are thus the jetsam of evolution. Those types which were forced into a new severe environment, began the evolution again by selection, and now furnish some of the highest minds - the Alpine type.