THE MEASUREMENT OF THE INTENSITY OF INBREEDING. I35 



may have been more. Whether it was or not is not a question 

 open to scientific determination Ijut only to speculation. 



From this table the following coefficients of inbreeding for 

 Figgis 20th are easily calculated. 



Zo = o 



Zi = o 



Z2 = 12.50 percent 



Zs =: 12.50 



Z4 = 21.88 " 



Zs = 25.00 " 

 Zo = 32.03 " 

 Zt = 35.94 " 



z^ = 37-30 " 



Z9 = 37.99 " 



Ziorr= 38.48 " 

 Zn = 38.57 " 



These coefficients show that Figgis 20th was at least 38 1-2 

 percent inbred. That is, she had rather less than two-thirds 

 as many different ancestors as she would have had in the event 

 of no inbreeding whatever. It is further clear that most of this 

 inbreeding took place in the fourth and earlier ancestral genera- 

 tions, chiefly in the fourth, fifth, and sixth generations. 



Comparing Figgis 20th v/ith Bess Weaver we see that the 

 latter is practically as much inbred in the first 4 ancestral gen- 

 erations as Figgis 20th is in the first 12. Considering in each 

 case only the first four ancestral generations the figures show 

 that, within these generations, Bess Weaver is exactly 3 times 

 more intensely inbred than Figgis 20th. 



The Relation of Coefficients of Inbreeding to the 

 Hereditary Constitution of the Individual. 



What, if any is the relation of coefficients of inbreeding to 

 the zygotic constitution (i. e., the hereditary make-up) of the 

 individual? Do the coefficients tell us anything regarding this 

 matter? A little consideration shows that they do. The suc- 

 cessive coefficients of inbreeding indicate the rate and degree 

 to which the possible number of different hereditary unit factors 

 present in the ancestry is subsequently reduced as a result of 

 inbreeding. They give no indication of the condition in which 

 the remaining factors are present (i. e., whether in homogvgous 



