44 



A. Comfort 



these fell in the same grouping interval. Of 1,492 lives, 1,342 

 were scored and grouped by age of dam, 1,355 by age of sire, 

 and 719 by both, the missing lives among these being scored 

 for one parent only — chiefly the progeny of imported horses, 

 of stallions whose dates of birth were not easily ascertainable 

 from the record, or of mares covered by more than one stallion 

 in the season. The distribution of parental ages is shown in 

 Fig. 2, and the results of the calculation in Table III. 



DISTRIBUTION OF PARENTAL AGES 

 THOROUGHBRED MARES 1875-1880 



DAM • 



SIRE O 



AGE:YRS 2 



Fig. 2. Mares foaled in 1875-80: distribution of ages of sires at 



covering (O) and dams at foaling (O) (Comfort, 1958a). 



Reproduced by courtesy of the Editor, Journal of Gerontology. 



There was no significant difference in expectation of life 

 between foals of mares under and over 13 years of age ( ^ 12, 

 e^^^ = 16-89; ^ 13, e^^^ = 16-86 years). With further sub- 

 division the progeny of the oldest mares had the shortest 

 lifespans, but the largest difference was less than twice its 

 standard error. Still smaller differences were obtained for the 

 same lives grouped by paternal age alone. Of the 719 lives 

 grouped by age of both parents, those whose dam and sire 



