CHAPTER X 



LONGEVITY 



Cell Division at Different Ages— Effect on Offspring 

 Produced at Different Ages of Parents — Genealogies — 

 Longevity of Different Offspring from the Same 

 Parents — Infant Mortality — Immunity — Fecundity 

 — Evolution. 



'T'HE doctrine of evolution assumes that 

 *■ different animals are blood relatives by 

 reason of descent from some common ancestor. 

 Of these relatives some normally live only a 

 few days, some a few weeks, others a few 

 months, still others a few years, and some live 

 nearly a century. These are natural periods of 

 life and the animals of each species reproduce 

 their kind before death. 



How did these striking differences in 

 longevity come into existence? It will prob- 

 ably be said that they came about through 

 fortunate variations. Quite true, but there 

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