But Hobbits have never, in fact, studied magic of any kind, and their elusiveness is due solely to a professional skill that heredity and practice, and a close friendship with the earth, have rendered inimitable by bigger and clumsier races.
There are no more uses of "hereditary" in the book.
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It is hereditary, but fortunately not contagious.
It is an unfortunate hereditary condition that is not easily detected even by the regular and thorough cardiac screening.