152 BIOLOGY OF DEATH 



dence that heredity plays any part at all in the deter- 

 mination of longevity. 



THE HYDE FAMILY 



The first material which we shall discuss is that pro- 

 vided by the distinguished eugenist, Dr. Alexander 

 Graham Bell, in his study of the Hyde family. Every 

 genealogist is familiar with the ' * Genealogy of the Hyde 

 Family/' by Reuben H. Walworth. It is one of the fin- 

 est examples in existence of careful and painstaking 

 genealogical research. Upon the data included in this 

 book, Bell has made a most interesting and penetrating 

 analysis of the factors influencing longevity. At first 

 thought one might conclude that highly biased results 

 would probably flow from the consideration of only one 

 family. Bell meets this point very well, however, in the 

 following words : 



A little consideration will show that the descendants did not constitute 

 a single family at all, and indeed had very little of the Hyde blood in them. 



Even the children of William Hyde owed only half of their blood to 

 him, and one-half to his wife. The grandchildren owed only one-quarter of 

 their blood to William Hyde, and three-quarters to other people, etc. The 

 descendants of the seventh generation, and there are hundreds of them, owed 

 only one sixty-fourth of their blood to William Hyde, and sixty-three 

 sixty-fourths to the new blood introduced through successive generations of 

 marriages with persons not of the Hyde blood at all. 



It will thus be seen that the thousands of descendants noted in the 

 Hyde Genealogy constitute rather a sample of the general population of 

 the country than a sample of a particular family in which family traits 

 might be expected to make their appearance. 



The substantial normality of the material is shown 

 in Figure 41, which gives the l x line, that is, the number 

 of survivors at each age, of the 1,606 males and 1,352 

 females for whom data were available. The solid line 

 is the male l x line and the dotted line the female l x . It 

 is at once apparent that the curves have the same general 



