ON THE INHERITANCE OF THE DURATION OF 
LIFE, AND ON THE INTENSITY OF NATURAL 
SELECTION IN MAN. 
By MARY BEETON, Girton College, Canibiidge, and KARL PEARSON. 
CONTENTS. 
Page 
(1) Introductory ; source of the statistics 50 
(2) Method of treating the statistics 51 
(.3) Influence of priority of birth on the relative duration of life of members of the 
same fiimily .............. 53 
(4) Influence of the death of minors on the death of adult brothers or sisters . . 57 
(5) Synopsis of numerical constants and equations for the prediction of the probable 
duration of life ............. 59 
(6) Comparison of present results with those previously obtained .... 63 
(7) Illustrations of prediction of duration of life : 
(i) Expectation of life from ages of death of four gi'andparents, and ages of 
living parents ............ 68 
(ii) Expectation of widowhood from age of husband and ages at death of children . 71 
(8) Calculation of the intensity of natural selection in the case of man ... 73 
(9) Natural selection in man, a fact, not an hypothesis 75 
(10) General results for inheritance ........... 76 
(11) Tables I— XXII, reduced data 76 
(1) In a first study of the Inheritance of Longevity presented to the Royal 
Society in June, 1899*, Miss Beeton and I confined our attention to the material 
then available, namely, inheritance in the male line of direct descent and the 
coirelation between the lengths of lives of brothers. In both cases we dealt only 
with adult lives. The limitation to the male line was enforced upon us partly by 
the practice of tracing pedigrees only through the male line, partly by the habitual 
* R. S. Froc, Vol. 65, p. 290. 
