g TRANSACTIONS OF WAGNER 



MENDEL AND HIS LAW 



often happens in lower animals by a single parent. But double parentage pro- 

 vides that the new creature shall have qualities different from any previously 

 existing creature of the same kind, because it has a new combination of the 

 quaHties of the two parents. It is said to be so nearly impossible to shuffle 

 and deal a pack of cards exactly the same way twice, that one might spend his 

 entire life shuffling and deahng and never accompHsh this end. But the possi- 

 bilities of development in the human species are far greater than the possi- 

 bilities of shuffling in a pack of cards, and the probabihty of two persons being 

 exactly alike is so slight that it probably never occurs, excepting in the case of 

 identical twins, who have in reahty developed from two halves of the same egg. 



It is most interesting to find that Mendel's law, with its dominant and re- 

 cessive characters, its pure hnes and its hybrids, is true for peas. The question 

 naturally arises how far does it hold in other realms. Hosts of research workers 

 are now carrying this problem into all sorts of fields. Guinea-pigs and rats, 

 pigeons and chickens, are showing us in one way or another that they too obey 

 Mendel's law. The most interesting question of all is, of course, in how far 

 man finds himself under the same inexorable law. The literature of heredity 

 in the human race is a doleful one. It has to do with diseases and deformity. 

 The reason for this is plain. Diseases and deformities, when at all unusual, 

 impress themselves so thoroughly that they are remembered to the third genera- 

 tion, while more amiable qualities or sHghter peculiarities are entirely forgotten. 

 We do not yet have records enough to carry the investigations very far. This 

 is now being remedied, and after a while we shall understand human heredity 

 as well as we do that of the guinea-pig or of peas. 



Meanwhile, there is one easily observed respect in which Mendel's law 

 seems to work out very clearly in human beings. The color of the iris of the 

 eye is due to one or two factors, as the case may be. If the coloring is entirely 

 due to pigment at the back of the iris, the eye will be blonde; blue if the iris 

 is thin, and gray if it is thick. If, on the other hand, there be coloring matter 

 on both front and back of the iris, then the eye is brunette to a greater or less 

 degree. Now the brunette eye is dominant over the blonde, hence you can 

 never tell whether the children of a brunette-eyed parent will be blonde or 

 brunette, because there may be a recessive blonde under any brunette and it 

 not show except in the offspring, but a blonde-eyed parent cannot conceal 

 brunette character because if present it would be dominant and hence show. 

 Accordingly, two brunettes of pure brunette ancestry will have only brunette 



