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And by the early 1970s our little parable of Sam and Sweetie is exactly what happened to the North American Golden Retriever. One field-trial dog, Holway Barty, and two show dogs, Misty Morn’s Sunset and Cummings’ Gold-Rush Charlie, won dozens of blue ribbons between them. They were not only gorgeous champions; they had wonderful personalities. Consequently, hundreds of people wanted these dogs’ genes to come into their lines, and over many matings during the 1970s the genes of these three dogs were flung far and wide throughout the North American Golden Retriever population, until by 2010 Misty Morn’s Sunset alone had 95,539 registered descendants, his number of unregistered ones unknown. Today hundreds of thousands of North American Golden Retrievers are descended from these three champions and have received both their sweet dispositions and their hidden time bombs. Unfortunately for these Golden Retrievers, and for the people who love them, one of these time bombs happens to be cancer. To be fair, a so-called cancer gene cannot be traced directly to a few famous sires, but using these sires so often increases the chance of recessive genes meeting—for good and for ill. Today, in the United States, 61.4 percent of Golden Retrievers die of cancer, according to a survey conducted by the Golden Retriever Club of America and the Purdue School of Veterinary Medicine. In Great Britain, a Kennel Club survey found almost exactly the same result, if we consider that those British dogs—loosely diagnosed as dying of “old age” and “cardiac conditions” and never having been autopsied—might really be dying of a variety of cancers, including hemangiosarcoma, a cancer of the lining of the blood vessels and the spleen. This sad history of the Golden Retriever’s narrowing gene pool has played out across dozens of other breeds and is one of the reasons that so many of our dogs spend a lot more time in veterinarians’ offices than they should and die sooner than they might. In genetic terms, it comes down to the ever-increasing chance that both copies of any given gene are derived from the same ancestor, a probability expressed by a number called the coefficient of inbreeding. Discovered in 1922 by the American geneticist Sewall Wright, the coefficient of inbreeding ranges from 0 to 100 percent and rises as animals become more inbred.
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