380 EVOLUTION OF PHYSICAL CHAKACTERS 



of the world in so obvious a manner that it need not be furthei 

 discussed.^ 



Warfare following upon migration may exterminate whol< 

 races. The Bushmen were apparently on the verge of extinctioi 

 at the hands of the invading Bantu peoples. In this manne 

 a peculiar physical type may be lost and another may becomi 

 of relatively greater prevalence. Migration may also be followec 

 by any degree of racial mixture. Many rash statements have beei 

 made by historians as to the biological results of crossing. Thi 

 consequences actually observed to follow upon a mixture of race 

 are to so large a degree the result of a conflict of traditions — i 

 subject with which we shall deal in a later chapter — that thi 

 purely biological effects of crossing may be very largely obscured 

 Bearing this in mind we may briefly refer to the conclusion 

 to be derived from recent biological work which bear on th 

 problem. Roughly speaking there are two possible kinds o 

 crosses between races. First there are crosses between the mos 

 clearly distinguished varieties such as white and black. Heterosis 

 or hybrid vigour, will be exhibited in a marked fashion in th 

 first generation. Heterosis, the underlying cause of which ha 

 only recently become apparent, is always at its height in the firs 

 cross. The increase of vigour, however, is not long maintained i] 

 subsequent generations. Further, each type, such as those whicl 

 we are considering, has a series of character complexes, buil 

 up through ages of selection and compatible with one another 

 and by crossing such complexes are broken apart. The chanc' 

 of gain, on the other hand, through the favourable re-combinatioi 

 of characters is small. On the average, therefore, the result o 

 such a cross is unfavourable. There may also be crosses betwee] 

 races exhibiting less differences. Again, heterosis will be visibl 

 on crossing. But in distinction to the results of the former kin( 

 of cross, the other results may not be unfavourable. Grea 

 variability may follow such a cross and this is on the whol 

 advantageous. Valuable character re-combinations may alsi 

 come to light. Thus we may say that, so long as there is not toi 

 great a difference between the races which cross, the results ar 



' There has been much discussion as to the effect upon the population of Franc 

 owing to the Napoleonic wars. The facts have been summed up by Havelocl 

 'El\ia(Essays in War Time, pp. 33 ff.), and it appears that without any question th 

 average physical constitution of the French was lowered ; most kinds of infirmities 

 for instance, became more frequent. 



