M. Beeton and K. Pearson 
65 
of the regression line of father or son ought to be "2253 ; for adult sons it is only 
•1016, but an examination of the diagram shows that it is much nearer 2 than "l 
for early manhood. Further, our own results show that it is actually ■2059 for a 
father and a minor son. Thus our original statement* that in youth and infancy 
the regression line for parent and child would approach nearer its theoretical 
position seems to receive confirmation. The tendencies which cause an individual 
to have a short life, i.e. to die before the age of 35, are largely inherited tendencies, 
and they shorten also the life of the parent. The tendencies which lengthen the 
life of an individual beyond sixty years are also inherited, and they appear as 
lengthening the parental life. But between 35 and 60 the relationship of dura- 
tion of life in parent and offspring is not very marked. We thus can distinguish 
an inheritance of brachybioty separated from an inheritance of longevity by a 
period of life in which the non-selective death-rate is predominant. The whole of 
Fig. 3. 
Fio. 4. 
Regression Line : Fathers on Sons. 
Regression Line : Mothers on Sons. 
~« 53 58 63 68 73 78 83 Probable Age at Death of Mother 
Probable Age at Death of Father 
* The reader must disregard the results for ages 93 and 98, for they are based on very few CEtses. 
Biometrika i 5 
