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Mutts Aren’t Always Healthier Dogs

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Studies show how dogs evolved—it started with food

animals, biology, Uppsala University, geneticsDogs have been at humankind’s side for thousands of years; we’ve bred them for size, ferocity, hunting assistance (actually, assistance of all kinds), and perhaps above all, companionship. Now, a number of studies show how dogs evolved from their wild wolf ancestors, and what all that breeding has led to.

A study led by researchers at Uppsala University of Sweden reported in Nature that dogs evolved from wolf ancestors by adopting a diet heavier on starches and other carbohydrates. By conducting next-generation whole-genome sequencing on both dogs and wolves, the researchers found a number of genes in dogs that differed from wolves. These genes were involved in various behaviors, and a significant set of genes controlled starch digestion and fat metabolism.

Thus, the dog evolved on its stomach. Literally. The Uppsala researchers believe that dogs branched out from wolves because they were adopting a diet heavier on starches, while wolves continued their mainly meat-based diet. Why did the dogs switch meals? At the time, human societies were becoming more farm-based, and our diets were also switching to heavier emphasis on grains. In addition, food was either stored or discarded, which made it much easier to procure than hunting. So, feeding a dog a heavy meat diet isn’t necessarily healthy.

Some researchers aren’t so sure that dog evolution is based entirely on diet. Greger Larson, a geneticist at Durham University in the UK, and Robert Wayne, a geneticist at UCLA, both think that saying dogs’ diets triggered evolution isn’t right. They think that other behavioral traits, such as linking up with human companions, may have played a stronger role. After all, the Uppsala team did find a number of behavior genes that diverged.

Since that evolutionary leap, however, we’ve been breeding dogs for all sorts of traits and tasks. But has all that breeding been healthy for dogs? Can breeding go too far?

One popular notion is that purebred dogs aren’t as healthy as the basic “mutt:” a dog that’s the mix of a number of breeds. A study of 90,000 purebred dogs and mongrels by the University of Calfornia, Davis, found, well, a mixed bag. While some conditions appear in purebreds, others are just as prevalent in mutts.

The UC Davis researchers discovered about 25,000 dogs that had at least one genetic disorder. When they compared disorders between mixed- and pure breeds, they found 13 disorders—cancers, adrenal gland disease and hip dysplasia—were common to both. Purebred dogs were more likely to have 10 disorders, including cardiomyopathy, elbow dysplasia and cataracts. One disease was particular to mutts—a specific type of knee injury. The data also showed one cause of death that affected mutts more than other breeds: being hit by an automobile.

The researchers saw patterns that suggested that dog breeds that are more recent or were bred from known lines (a practice that can preserve pathogenic mutations) were more likely to suffer from disorders that were known among purebred dogs. Meanwhile if a mutt had a genetic disorder, it was more likely from something that affects all dog breeds, regardless of lineage.

And they’ve all evolved to eat the same food.

Sources: Los Angeles Times, Nature

Bellumori TP, Famula TR, Bannasch DL, Belanger JM, & Oberbauer AM (2013). Prevalence of inherited disorders among mixed-breed and purebred dogs: 27,254 cases (1995-2010). Journal of the American Veterinary Medical Association, 242 (11), 1549-55 PMID: 23683021

Axelsson E, Ratnakumar A, Arendt ML, Maqbool K, Webster MT, Perloski M, Liberg O, Arnemo JM, Hedhammar A, & Lindblad-Toh K (2013). The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature, 495 (7441), 360-4 PMID: 23354050

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