484 ANITA NEWCOMB MCGEE 



direction, but merging is a far more general term. Because you and I had 

 some ancestors in common a thousand years ago, it seems to me a misuse 

 of the word to say that we are "inbred." But some of our ancestral lines 

 have certainly "merged." 



Merging occurs whenever sibs appear among one's ancestors. When 

 two sibs appear in the same generation their parents have a double ancestral 

 value, and the number of different persons in the earlier generation is re- 

 duced by two. "Once merged always merged," hence the gap in a chart 

 produced by this so-called ^ancestor-loss" doubles with every preceding 

 generation and correspondingly reduces the number of ancestral persons. 



Two half sibs in the same generation produce half the effect of two whole 

 sibs; three sibs give their parents a three-fold ancestral value and create a 

 gap twice as big as that from two sibs. Four sibs create three times the gap 

 that two sibs do. In other words, the appearance in a chart of two children 

 of any ancestral couple causes a "loss" of two persons in the preceding gener- 

 ation, but four children in one generation cause a loss of six persons. 



The further back one goes, the more often do sibs occur in different gen- 

 erations, and also in more widely separated ones. This appearance of sibs 

 in different generations is due to the difference in age of the children in 

 one family and also to the difference in age of the parents caused by the 

 different generation-length of the sexes. Because the period of fertility of 

 women begins and ends earlier than that of men, the average length of a 

 human female generation is shorter, hence distinctly different from the male 

 generation-length. [I stress this because I have not found any writer on 

 this subject who recognized this distinction, so essential to correct calcu- 

 lation.] This does not mean that we have more ancestors of one sex than 

 of the other, for each couple represents both sexes. It does mean that 

 persons in or near the male line were born earlier than those in the same 

 generation who are near the female line, the difference increasing as we go 

 back. 



The "spreading" of ancestral lines is what occurs in the absence of merg- 

 ing. The relative frequency of the two conditions depends on the existence 

 of natural geographic limits or, among humans, on artificial restrictions on 

 marriage; tribal, national, social or religious. Merging is greatest among 

 small groups, such as the inhabitants of an island, or rank-maintaining 

 European royalty. If, and when, any group becomes entirely isolated, the 

 permanent ancestors in its first generation must in time become ancestors 

 of the whole group. So far as recorded genealogies go (looking backward), 

 the beginning of this process of merging is clearly shown, but it is always 

 interrupted by a break-down of the isolation and introduction of foreign 



