350 THE AMEBIC AX X AT U BALIS T [Vol. XLVI 



time, they must be crowding upon the original form. 

 Other examples in great number will occur to any one. 

 Thus there can be little doubt that primitive man was 

 dark-skinned and dark-eyed. The various modern races 

 were produced — so far as skin-color and eye-color are 

 concerned— by dropping out the factors (determiners) 

 for these characters. In our own Caucasian race, it 

 seems not unreasonable to suppose that we are tending 

 toward a condition of blondness, for there seems to be no 

 natural or sexual selection against this character. 9 



I am not unmindful of the fact that an apparently un- 

 important character such as righthandedness may be 

 bound up with other characters of great consequence. 

 In such case lefthandedness might mean, for example, a 

 distinct inferiority in metabolic activity. 10 Unless the 

 recessiveness is associated with weakened nutrition or 

 other enfeebled condition, it would seem most natural 

 for elementary species, when once originated, to increase 

 in number of individuals by continued mutation. 



Dr. Shull points out in his paper previously cited on 

 " Elementary Species and Hybrids of Bursa" that reces- 

 sive mutants may have an advantage over dominant mu- 

 tants if fluctuating conditions tend to eliminate now one 

 form, now the other. The killing off of dominant mutants 

 may be easily accomplished, but this is not the case with 

 recessives. 11 This is perhaps only another way of sta- 

 ting the well-known fact that it is hard in plant or animal 



• The claim that light-skinned and light-eyed people are not adapted to 

 sunny climates seems hardly substantiated. 



10 Cf. the observations by Professor Thomas Hunt Morgan upon .mutants 

 of the fruit fly, Drosophila, in the Journal of Experimental Zoology, Vol. 

 XI, p. 408, 1911. 



"To use his own words: "The recessive mutant may be preserved 



successful parent. Such prolongation of the life of a recessive may serve 



various distributing agents have carried it beyond the limits of the habitat 



This same idea has been suggested by my colleague, Professor T. D. A. 

 Cockerell, in a conversation regarding the general question of increase of 



