16 PRINCIPLES OF STOCK-BREEDING. 



even under the disadvantages of privation and hard 

 labor. 1 



The duration of the life of an individual is deter- 

 mined, to a great extent at least, by inheritance. The 

 members of some families die at an early age, while in 

 other families a ripe old age may be reasonably expect- 

 ed. The life-tables that have been constructed show 

 the average expectation of life of the masses ; while the 

 expectation of life of an individual can only be approxi- 

 mately determined by the age attained by his ancestors. 



Darwin mentions " the case of four brothers who 

 died between the ages of sixty and seventy, in the 

 same highly-peculiar comatose state. 2 . . . 



" It is now generally understood that longevity 

 depends far less on race, climate, profession, mode of 

 life, or food, than on hereditary transmission." 



There are long-li ved families under what would be 

 considered unfavorable conditions for longevity, while 

 other families are short-lived under the most favorable 

 conditions for the promotion of health. " The aver- 

 age of life," says Dr. Lucas, "plainly depends on 

 locality, hygiene, and civilization, but individual lon- 

 gevity is entirely exempt from these conditions. 

 Everything tends to show that long life is the result 

 of an internal principle of vitality, which privileged 

 individuals receive at their birth. It is so deeply im- 

 printed in their nature as to make itself apparent in 

 every part of the organization." 8 



1 " Heredity," by Ribot, p. 3 ; Colin, " Physiologic Comparee," tome 

 ii., p. 634. 



3 "Animals and Plants under Domestication," vol. ii., p. 28. 



'"Heredity," by Ribot, p. 5; Smith's "Physical Indications of 

 Longevity," p. 3. 



