Have Dogs Specifically Evolved to Eat Bread and Pasta?
The battle over what is the most natural, appropriate and healthy diet for dogs continues. I recently witnessed another round of this conflict when I was invited to a casual dinner under the canopy of an RV following a day of competition at an outdoor dog show. The menu consisted of salad, spaghetti, and cold beer. One of the dog owners attending this little dinner party had pretty much finished eating but still had about a half cup of spaghetti left on her plate. So in a typical gesture that most of us recognize, she put the plate down on the ground for her Golden Retriever, Toby, to eat. It took only a few milliseconds for him to vacuum it up, and he was looking at his owner hoping that more might arrive when one of the other dog owners almost screeched at her.
« What are you doing? » she asked in a strident voice. « You should know better than that. Dogs are carnivores, just like wolves, and are supposed to be eating raw meat and bones. Giving them all of those starchy carbohydrates is damaging their health. That’s why I put my dogs on a BARF [bones and raw food] diet. They are happier and healthier because they are now eating a diet that they were genetically designed for. »
The spaghetti woman picked up the now clean plate and said « Actually Toby’s favorite foods are pasta, saltine crackers, and left over pizza crusts. My understanding is that dogs are really scavengers and can safely eat anything. » She turned to me and said, « You’ve written about this raw food diet for dogs [click here to see that] and as I recall you didn’t find any real benefits, and maybe even some problems with it. But what about this idea that dogs are pure carnivores and because of their genetics they won’t thrive on anything other than meat and bones? »
The answer to her question is a bit complicated and there are a few blank spots that still have to be filled in. Most of the genetic evidence says that the animals that we recognize as dogs emerged in the Neolithic period. That would be just about the time when humans were beginning to transition from a hunter-gatherer lifestyle to one involving agriculture and fixed settlements. If dogs were domesticated around this time that actually has some important implications for how dogs have diverged genetically from wolves.
A study headed by Erik Axelsson from the Department of Medical Biochemistry and Microbiology at Uppsala University in Sweden attempted to learn more about the evolution of canines by comparing the DNA sequences of modern dogs and wolves. They report that dogs do show some distinct differences from wolves in the genes that control important functions. One set of differences was expected, and this involves the genetic control of brain development. The other was totally unexpected and it had to do with digestion, specifically of starches and carbohydrates.
This was a large study involving some complex analyses. Basically the researchers combined samples from 60 different dogs of 14 different breeds ranging from fairly modern breeds, like spaniels and retrievers, to fairly wolflike dogs such as elkhounds. The researchers did a bit of genetic magic by sequencing different parts of the genome in each breed tested and then they merged them together to create a sort of a master, composite, dog reference genome. They also did a similar form of synthesis based on samples of 12 wolves in seven countries to create a master wolf reference genome.
Their results show that eight of the genes which differ between wolves and dogs are associated with brain development, and these differences might explain things like why wolves turn out to be aggressive and dogs generally don’t. This also can explain why dogs keep many of their puppy-like characteristics and behaviors when they become adults while wolves do not. This confirms what we had always suspected, namely that many of the behavioral and personality differences between dogs and wolves are genetically based.
However there was a surprise in another area, namely some differences in the genes controlling digestion. Dogs break down the kind of carbohydrates that we usually call starch, in three digestive stages. These researchers found genetic differences which were related to each of those stages. Their strongest example is the alpha-amylase gene called AMY2B, which is involved in the processing of starch in the pancreas. While the wolf genome carries two copies of this gene dogs carry anywhere from 4 to 30 copies. Furthermore chemicals associated with the digestion of carbohydrates which are influenced by AMY2B, are 28 times higher in the pancreas of dogs and nearly 5 times higher in their blood.
What these results mean in simple terms is that dogs evolved a mechanism for digesting carbohydrates that wolves don’t have. While this was a truly surprising finding, it fits well with the scavenger hypothesis about how dogs were domesticated. This is the hypothesis which says that wild canines began to hang around human settlements to eat the scraps of food that humans tossed into their garbage heaps. Since this was the dawn of organized agriculture more grain-based starches and carbohydrates were beginning to make their way into the human diet. Through natural selection, the wild canines that could best process and survive on such a starch-based diet would obviously thrive the best and produce the most offspring. Over generations natural selection would cause a set of genetic differences to evolve, eventually leading to our domesticated dog with a good ability to process such foods. The researchers summarize their conclusions saying « Our results show that adaptations that allowed 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 early dog domestication. »
Now here is the kicker — human studies suggest that people also picked up extra copies of that alpha-amylase gene during the agricultural revolution. The researchers say « The results presented here demonstrate a striking case of parallel evolution whereby the benefits of coping with an increasingly starch-rich diet during the agricultural revolution caused similar adaptive responses in dog and human. » In other words, we have evolved and our dogs have co-evolved in lockstep to the changing nature of our food supply.
So what does this research say about whether it is necessary, or advantageous, to put our dogs on an expensive raw-meat diet? That diet is based upon an attempt to mimic the kinds of food that wolves naturally eat in the wild. Certainly it is true that if we took a wolf out of the wild and fed him on a diet which contained mainly starch and carbohydrate he might not thrive. A wolf deprived of his mainly meat-based diet might be expected to show severe declines in his health.
The raw meat and bones diet is based on the hypothesis that dogs and wolves are genetically the same and have the same physiology. The data from this current investigation shows that that hypothesis is wrong. The data collected here confirms that there are significant genetic differences between dogs and wolves in important areas. The simplest way to summarize this is to say that dogs are not wolves and therefore designing regimes of any sort, whether dietary or behavioral, based on what we know about wolves is wrong. The most important example of the difference between dogs and wolves which is demonstrated by this current research is that dogs have special digestive equipment for handling carbohydrates which wolves do not. That means that you can safely give your dog some of your leftover spaghetti or a piece of bread, and you can continue to save the crusts from your pizza to give to your dog as snacks.
Stanley Coren is the author of many books including: Gods, Ghosts and Black Dogs; The Wisdom of Dogs; Do Dogs Dream? Born to Bark; The Modern Dog; Why Do Dogs Have Wet Noses? The Pawprints of History; How Dogs Think; How To Speak Dog; Why We Love the Dogs We Do; What Do Dogs Know? The Intelligence of Dogs; Why Does My Dog Act That Way? Understanding Dogs for Dummies; Sleep Thieves; The Left-hander Syndrome
Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission
Erik Axelsson, Abhirami Ratnakumar, Maja-Louise Arendt, Khurram Maqbool, Matthew T. Webster, Michele Perloski, Olof Liberg, Jon M. Arnemo,, A˚ ke Hedhammar & Kerstin Lindblad-Toh (2013). The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature, 495, 360-365. doi:10.1038/nature11837