EFFECTS OF INBREEDING AND CROSSBREEDING. 55 



rities genetically, heterozygous in many respects, among whose 

 descendants any trait was likely to segregate out. That one or two 

 of the males transmitted extreme degrees of two characters is a mere 

 coincidence on the view suggested above and would not be expected 

 to happen with other characters. 



The absence of correlation between the characters finds extreme 

 illustrations in most cases. Compare, for example, Family 23, in 

 which the young were born alive with great success, but died in 

 unusually large numbers before weaning, with Family 13, in which 

 the reverse was true. Families 17 and 3 have already been noted 

 as families which were successful or failed in both respects. Families 

 11, 21, 19, and 1 show extremes of size and frequency of litters, com- 

 bined in four different ways. Even in the case of birth weight and 

 gain, some independence may be noted. In Family 39 the young 

 made better gains in both periods than their birth weights indicated 

 as most likely, while the opposite was true of Family 19. 



RECORDS OF FIVE FAMILIES IN RECENT YEARS. 



As already noted, most of the inbred families have been disposed 

 of since 1915 to make room for a more intensive study of the five 

 which have been retained, Nos. 2, 13, 32, 35, and 39, and for experi- 

 ments on crossbreeding. The data for years 1916 to 1919 is pre- 

 sented in Bulletin 1121. It is desirable here, however, to com- 

 pare the standing of the above-mentioned five families in 1916-19 

 with their standing in the earlier periods. This is especially true be- 

 cause two of these families, Nos. 2 and 35, were the ones among the 

 original 22 which showed the greatest change in character from the 

 first to the second period. The rank in various characters of the five 

 remaining families is shown in Table 6 for the three periods together 

 with rank in longevity of the males and females (1915-1918) and 

 resistance to tuberculosis during 1919-20. The resistance to tuber- 

 culosis has been obtained in experiments in cooperation with Dr. Paul 

 A. Lewis, of the Henry Phipps Institute. (Wright and Lewis, 1921.)° 



The correlation between the ranks in the first and second, the first 

 and third, and the second and third periods are shown in the last 

 three lines of Table 6. A single correlation based on five entries 

 does not, of course, have much significance by itself. It will be 

 seen, however, that while the correlation between standing in the 

 first period and the second or third is negative in almost as many 

 cases as it is positive, all of the correlations between the second and 

 third periods are positive, and most of them are high. Their average 

 is +0.75, where +0.04 and +0.01 are the averages in the cases of the 

 correlation of first with second and third period respectively. The 



s See footnote 3. 



