M. Beeton and K. Pearson 
59 
that person's expectation of life. In the case of the man, indeed, it is an advantage 
for his brother to die as an infant rather than as an adolescent ; this is, of course, 
due to the effect of the mortality of youth being sensible in the early years of 
adult life, and influencing the heritage. It appears to have much less influence in 
the case of sisters. One word here about the influence of environment. There 
may be some readers who will be inclined to consider that much of the correlation 
of duration of life between brethren is due to there being a likeness of their 
environment, and that thus each pair of brethren is linked together and differen- 
tiated from the general population. But it is difficult to believe that this really 
affects adult brothers or a father and his adult offspring. A man who dies 
between 40 and 80 can hardly be said to have an environment more like that of 
his brother or father, who died also at some such age, than like any other member 
of the general population. Of course two brothers have usually a like environ- 
ment in infancy, and their ages at death, even if they die adults, may be 
influenced by their rearing. But if this be true, we ought to find a high 
correlation in ages at death of bi-ethren who die as minors. As a matter of fact 
this correlation for minor and minor is 40 to 50 per cent, less than in the case of 
adult and adult. It would thus seem that identity of environment is not the 
principal factor in the correlation between ages of death, for this correlation is far 
less in youth than in old age. 
(5) The following Table summarises our chief results : 
