The Biology of Senescence 



exclusively from old individuals, appear to be cumulative and 

 reversible (p. 88). 



The general question of maternal age effects in genetics is 

 beyond the scope of this book. It has recently been reviewed 

 (Miner, 1954) in a valuable symposium. In mammals the age of 

 the mother exerts an influence on the vigour of the progeny 

 which appears to vary greatly in direction and extent, even 

 within a species. Sawin (in Miner, 1954) found that in one 

 strain of rabbits, the early ( < 6 months) mortality was lowest 

 in the progeny of young mothers, and increased throughout 

 maternal life, while in another, larger, strain it reached a 

 minimum in the progeny of mothers 18 months old. These 

 changes were not correlated with any differences in lactation or 

 maternal weight. Jalavisto (1950) found evidence that in man 

 the expectation of life decreases with increasing maternal, but 

 not paternal, age. The percentage of abnormal offspring is 

 greatest in litters born to young guinea pigs (Wright, 1926) and 

 elderly women (Murphy in Miner, 1954). It is possible that the 

 association of mongolism with high parental age is a reflection 

 not of increasing foetal abnormality, but a decrease to the point 

 of viability in an abnormality which, at younger maternal ages, 

 is lethal (Penrose in Miner, 1954). In some celebrated experi- 

 ments upon mouse leukaemia, McDowell and his co-workers 

 have shown that when susceptible males are crossed with 

 resistant females, the age of onset of leukaemia in the hybrid F x 

 is significantly retarded in mice born to, or suckled by, old as 

 compared with young mothers. At the same time, the mean 

 longevity of mice which die of causes other than leukaemia is 

 also greatest in the progeny and nurslings of old mothers 

 (McDowell, Taylor and Broadfort, 1951). Strong (in Miner, 

 1954) has described a factor influencing the latent period of 

 sarcoma production after injection of methylcholanthrene into 

 mice, which appears, like Lansing's rotifer longevity factor, to be 

 cumulative — a line derived from seventh to ninth litters in each 

 generation had a significantly increased and increasing latent 

 period compared with a line derived from first and second 

 litters. Unlike Lansing's effect, this increase has not been shown 

 to be reversible in the progeny of young members of the 'old' 

 line. There is at present no evidence in mammals of any 



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