THE GROWTH OF GROUPS 61 



The assumption is based on the following observed 

 facts. Ten rats of this special kind were captured in the 

 same place at one time. The ten were pure black in 

 colour. The skulls of four of them were examined and 

 found to be of the special type. The circumstances did 

 not allow of a fuller investigation than this, but the 

 assumption became justified later on. It was desirable 

 to collect more facts about the group, consequently it 

 was arranged that any further specimens obtained 

 should be sent to me. Although the same rate of destruc- 

 tion was maintained, it was not until nearly six months 

 later that two others were obtained. They were caught 

 in the neighbourhood of Maung Khyine Street, but the 

 actual house from which they were taken was unknown. 

 Both showed clearly the characters which are the peculiar 

 property of the Maung Khyine group. Hence we may 

 be sure that they were derivatives of that group. If, as 

 might have been the case, they had been black, but not 

 large and with a narrow skull, they would not have 

 been derivatives of the Maung Khyine group, but of some 

 other group of independent origin. 



How, now, did this family group arise ? The progeni- 

 tors of the group were either born in Rangoon of normal 

 brown parents or they are migrants from without. In 

 my opinion there is no other explanation, for we cannot 

 suppose that effectual selection for melanosis occurred 

 in and around two houses only, among all the houses of 

 Rangoon. Hence those who believe in gradual evolution 

 must suppose that the progenitors of the group were 

 migrants from without. Their position is unassailable, 

 for it can never be proved that there is no such race in 

 any part of the world, from which migration by some 



