556 



THE AMERICAN NATURALIST [Vol. LI 



here described it is exactly expressible in the form 

 K, = 50, K, = K, = lb. 



5. It will be perceived that the form of relationship 

 coefficient here proposed leads to precisely the same 

 numerical results in simple pedigrees, with not too in- 

 volved inbreeding or kinship, as that given in my former 

 paper^ except for the fact that I have here changed the 

 subscript designation of the ^'s to bring them into con- 

 formity with the total inbreeding coefficients. The earlier 

 form proposed for these coefficients would always give the 

 same numerical values as the present one if certain rather 

 complicated rules of application, which were not clearly 

 or rigorously set forth in the earlier paper, were to be 

 followed. But the present simplified form does away en- 

 tirely with the need for these complicated rules of pro- 

 cedure. 



6. It is of interest to set forth in tabular form the 

 values of the relationship coefficients for the commonly 

 recog-nized degrees of kinship. This is done in Table 

 VIII, in which the different degrees of kinship are ar- 

 ranged in descending order of closeness, in general. In 

 some cases, as, for example, parent and offspring and 

 half brothers (or half sisters), groups of two or three 

 different sorts of kinship showing the same numerical 

 degree of relationship should be regarded as bracketed, 

 since there is no more reason for placing one of these 

 first than another. 



From this table a number of interesting points emerge. 

 AVe note that the absolute maximum of closeness of re- 

 lationship is that of brother and sister. The parent and 

 offspring relationship is one half as close. Uncle and 

 nephew (or niece), or single first cousins, are twice as 

 closely related as grandparent and otfspring. Some of 

 these comparisons made obvious by the table may seem at 

 first thought to give unexpected results, but if one will 

 take the trouble to write down pedigrees for the stated 



1 Pearl, E., Ameh. Nat., Vol. XLVIII, pp. 513-523, 1914. 



