THE INHERITANCE OF DURATION 159 



cases. Where one parent, but not the other, lived to be 

 80 or older, 9.8 per cent, of the offspring lived to be 80 

 or older, the percentage here being based upon 583 cases. 

 Where both parents lived to be 80 or older 20.6 per cent, of 

 the persons lived to the same great age, the percentage be- 

 ing based upon 184 cases. Thus it appears that in this 

 group of people four times as many attained great longev- 

 ity if both their parents lived to an advanced age, as 

 attained this age when neither parent exhibited great 

 longevity. The figures from the Hyde family seem fur- 

 ther to indicate that the tendency of longevity is inherited 

 more strongly through the father than through the 

 mother. Where the father, but not the mqther, lived to 

 be 80 or older, 11.3 per cent, of the persons lived to age 

 80 or more, there being 337 cases of this kind. Where 

 the mother, but not the father lived to be 80 or older, 

 only 7.7 per cent., or nearly 4 per cent, fewer of the 

 persons lived to the advanced age of 80 or more, there 

 being 246 cases of this sort. Too much stress is not, 

 however, to be laid upon this parental difference because 

 the samples after all are quite small. 



One other point in this table deserves consideration. 

 Out of the 1,594 cases as a whole, less than 9 per cent, 

 of the persons lived to the advanced age of 80 or more. 

 But out of this number there are 767, or 48.1 per cent., 

 nearly one-half of the whole, who had parents who lived 

 to 80 or more years. 



Another interesting and significant way in which one 

 may see the great influence of the age of the parents at 

 death upon the longevity of the offspring, is indicated 

 in Table 16, where we have the average duration of 

 life of individuals whose fathers and mothers died at 

 the specified ages. 



