dogs, diets, & the impact of evolution

Yvonne d'Entremont (aka SciBabe) recently posted an article on 'alternative' foods and health products for pets, in her usual no-holds-barred style. It's always good to see pseudoscience called out for what it is, and in the case of pet-focused quackery it's a message that needs multiple repeats. Why? Because pets are dependent on us, & we have a responsibility to get things right. Homeopathy is not going to clear a dog of tapeworms, and garlic (often advocated as a flea treatment) is actually rather toxic to cats.

As she says

My Buddy is 11 lbs. He’s afraid of the rain. He needs prescription dog food or else crystals build up in his urinary tract and he pisses blood. He and nature don’t coexist very well. Nature really doesn’t give a shit whether Buddy lives or dies. And since I do care, I’m not so sure that we should use nature as a credentialed source of vitality for a small animal who fears common weather phenomena. Most pets aren’t “natural,” they’re domesticated. They live and thrive on our care.

So much like with human health, don’t leave it up to the internet. Bring your questions about your animal’s health to your veterinarian. Keep observing their behavior and any changes to skin, coat, reactions to food, energy levels, and weight. Get them vaccinations and preventative treatment for appropriate things like fleas and heartworm.

At one point, d'Entremont discusses various diet fads for pets, including veganism (for cats, which are obligate carnivores!!!) & raw food diets. One of her links is to a Nature paper on the impact domestication has had on dogs' digestive systems (Axelsson, Ratnakumar, Arendt, Maqbool et al., 2013), which reports on the genomic evidence for adaptation for a diet that contains a lot more starch than dogs' progenitors, wolves, would ever eat.

That adaptation has occurred over at least 10,000 years. Axelsson & his colleagues note that bones found in burials with humans, from an Israeli site that dates back to 12,000 years before present (ybp) could well be the earliest confirmed dog remains. They cite genomic data suggest that canid domestication began in SE Asia, or the Middle East, around 10,000 ybp, but also comment that the evolution of domestic dogs may well have begun in several regions at much the same time.

While we don't know why dogs were domesticated, it's likely that traits enabling cohabitation with humans would have undergone relatively strong selection: Axelsson et al. suggest that these could include behavioural traits such as reduced aggression and changes in abilities related to social interactions, along with morphological features. 

This paper is based on whole-genome sequencing of both wolves and dogs, in order to identify regions of the genome that might have been subject to natural selection as dogs became domesticated. The research team identified 19 regions that contain genes involved in brain functioning, including several that might be involved in behavioural changes.

But they also found 10 genes key to starch digestion & fat metabolism that also appeared to have undergone evolutionary change during domestication. These genes are involved in breaking starch down into maltose (& other smaller molecules), digesting these molecules into glucose, and moving the glucose into the cells that line the intestine. In humans, salivary amylase begins this process in the mouth, but dogs produce only pancreatic amylase – and the team found a marked increase in the number of copies of the gene coding for this form of amylase in dogs, compared to wolves. They also identified mutations in dogs that could enhance the actual uptake of glucose.

They concluded that 

Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves, constituted a crucial step in the early domestication of dogs. 

In other words, dogs are no longer adapted to a wholly-carnivorous diet. But nor are they suited to veganism. Fad diets for pets are not a good idea. 


E.Axelsson, A.Ratnakumar, M-L.Arendt, K.Maqbool, M.T.Webster, M.Perloski, O.Liberg, J.M.Arnemo, A.Hedbammar & K.Lindblad-Toh (2013)  The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature 495: 360-364. doi:10.1038/nature11837


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