58 
Inheritance of the Duration of Life 
tions of life of adult and infant brethren. Without ravich more material than we 
have been able to accumulate I do not believe we could safely break up our data 
and correlate the duration of life of adults with that of infant brethren dying 
under 10 or 12 years of age. I think we must conclude : That to have a brother or 
sister die as a minor considerably sliortens the expectation of life, but whether the 
brotlier or sister dies at 2 or 5 or 10 or 15 does not make a difference which we 
can at present, without further data, consider as sensible. 
The general effect on the duration of life of an adult produced by the death 
of a brother or sister in their minority is shown in the following table : 
Average Age at Death. 
If there has died 
Of adult brother 
1 
Of adult sister 1 
1 
Adult elder brother 
Adult younger brother 
Minor brother ... 
Adult elder sister 
Adult younger sister ... 
Minor sister 
54-575 
58-560 
49-009 
1 58-804 1 
48-201 
I 57-209 
46-135 
55-667 
59-924 
50-300 
It is remarkable that the death of his sister as minor seems more important to 
a man than the death of his brother as minor, and vice versa for a woman. I 
have dealt with this a little more closely by averaging the age at death of men 
and women who have lost brothers or sisters in infancy, i.e. before 11 years of age. 
I find: 
Average Age at Death. 
If there has died 
Of adult brother 
Of adult sister 
Infant brother 
50-116 
46-027 
Infant sister 
47-830 
50-236 
The probable error is in each case under a year so that the results are signifi- 
cant. One would like to see the whole matter investigated with the ample 
material which could only be provided by large assurance offices. But our results 
suggest that some diseases to which a family may be prone are more liable to 
attack one sex in infancy and the other in the adult period. 
The above averages suffice also to indicate that whether a person's brother or 
sister dies as an infant or between 10 and 21, there is no very large difference in 
