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Dogs have the widest range of body sizes among mammals.
The size differential between the largest dog, the Great Dane, and the smallest, the Chihuahua, appears to be due to a single gene which suppresses IGF-1, an "insulin-like growth factor 1" hormone.
This single-gene hormone-suppression appears only in domestic dogs, and only in the smaller dogs such as the Jack Russell Terrier.
Suppression of the IGF-1 appears to be associated with a longer life span. Conversely, animals across a wide variety of species have been shown to have an increased risk of death from age-related diseases such as cancer and heart disease if higher levels of IGF-1 are present.
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2 comments:
Uh-oh - I just got two mixed mastiff pups from the shelter...
Well this is true to some extent but we lost our Anatolian shepherd last year at almost 14 years old...modern breeding practices have been a major cause of shortened lifespans in giant breeds. If breeders cared to outcross and take other steps to achieve longer lifespans, they could make a difference. Sadly health and longevity are not a concern for the vast majority of conformation breeders.
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