Other Kinds of Hybridizing 167 



The Mendelian inheritance of coat color in mice and in some 

 other animals may give an exaggerated idea of the inheritance of 

 color in general. That the inheritance is not always of this sort 

 seems to be shown by a number of cases, some of which have been 

 given. Pearson's examination of the inheritance of color in the 

 coat of dogs, horses, and of the eye color in man, has led him to 

 conclude that in these cases there is no evidence of Mendelian 

 inheritance. He points out that when the whole range of the 

 ancestry is examined we get more nearly an idea of what the 

 color of the offspring will be. For example, in one case, where 

 the color of the eye of the mother and of the father was blue, 

 only two of the children had blue eyes; but in another case, where 

 the father and the mother and all four of the grandparents and 

 five recorded grandparents had blue eyes, four children had blue 

 eyes. Single cases of this kind in themselves do not show much, 

 but these are only samples of what is generally found in many 

 cases of the sort. Pearson thinks that the prediction of what 

 the color of the eyes is likely to be will be closer when we use the 

 ancestry and not the parents alone. If any of these eye colors 

 follow the Mendelian rule of dominance and recession, some evi- 

 dence of this would appear in the statistics, but nothing of the 

 sort has been found. 1 It is evident, nevertheless, that these 

 cases require careful reexamination, since there has probably 

 been great intermingling of different ~ colors in the past. 



De Vries and some other students of mutation have laid much 

 stress upon the immutability of unit characters. De Vries as- 

 sumes that transitions between unit characters exist as little as 

 between the molecules of chemistry. It cannot be maintained, 

 I think, from the evidence that we possess, that unit characters 

 are immutable, for there are some cases in which it appears that 

 the unit character may be halved by every crossing. It is true 

 that some of these cases may be explained by antagonistic char- 

 acters both developing and mutually influencing the result ; but if 

 they do not subsequently separate, it is impossible to tell whether 

 or not a new unit character has been formed by combination. 



1 " The Law of Ancestral Heredity," Biometrica, II, 1903. 



