HISTORICAL CYCLES — CRAWFORD 449 



regions where life is hard into those where it is easier. Inured to 

 striving in their homeland, the invaders have developed by natural 

 selection into a race of hardj?^ folk; and the impetus of their more 

 energetic mode of life carries them forward, in the better land of 

 their adoption, to greater and higher achievements than the natives. 

 They " thrive vastly " there, " until their tone is let down to tlieir 

 conditions" (p. 125). There are, moreover, many new problems of 

 adjustment to be solved. When this is achieved and a regime of liv- 

 ing established, complete freedom of expression is soon gained and 

 " strife being ended, decay sets in shortly after." The accumulation 

 of capital contributes to the same result, by lessening the need of 

 effort. " The maximum of wealth must inevitably lead to the down- 

 fall " (p. 126). 



Changes of climate may be another contributory cause, and periods 

 of desiccation do actually coincide with periods of migration, but they 

 do not (Petrie thinks) account for the regularity of the phase. This 

 he attributes to the lapse of time required to effect a complete fusion 

 of different racial stocks, which he calculates should take from six to 

 eight centuries, and the explanation, wherever it can be tested by the 

 facts of history, seems adequate. " The complete crossing of two races 

 produces the maximum of ability, and * * * from that point 

 repeated generations diminish the ability * * *, Bi^it probably 

 each of the other causes before noted may bear a part " (p. 124). He 

 concludes with the suggestion that " eugenics will, in some future 

 civilization, carefully segregate fine races and prohibit continual 

 mixture, until they have a distinct type, which will start a new 

 civilization when transplanted. The future progress of mankind 

 maj'- depend as much on isolation to establish a type as on fusion 

 of types when established " (p. 131). 



As a corollary of this we would add that the longer a culture re- 

 mains isolated, developing along its own lines, the more specialized it 

 becomes and the less easy it is to cross it with another. It gradually 

 becomes a different species. It is a biological fact that the mating of 

 individuals of different species is infertile. Too great contrasts 

 produce sterility. It seems also to be a rule of history that when a 

 higher (or more advanced) culture invades and conquers a lower it 

 exterminates it and often the people too. Thus the Koman invasion 

 killed late Celtic art in Britain, and western civilization has proved 

 fatal to many primitive races. The invasion of one barbarism by 

 another is also infertile and might perhaps be compared with the 

 marriage of children. It seems as if the relative age of mating 

 cultures has got to be exactly right, as well as the degree of their 

 affinity. 



