“Where goeth the food, so goeth the dog.” (old proverb)
The earliest archeological evidence dates dogs to about 14,000 years ago. Remains of small dogs in Israel go back 12,000 years. When people settled down in agricultural communities, they began to tinker with the natural environment, bringing about modification, intentionally or accidentally, in plants and animals. Of course dogs joined the party. They always do.
Not everyone agrees about why, where, when or how dogs evolved. But we all believe this: Whether dog domestication was accidental or intentional, abrupt of slow, happened 10,000 years ago or 80,000, domestic dogs descended from wolves and evolved with people. Perhaps it’s no coincidence then that we ask the same questions about dogs that we do of ourselves: How are we unique? Where do we come from? And when did we get here?
On Wednesday, January 23, canine geneticists announced they have identified key mutations in three genetic regions that allowed the wolf, a traditional carnivore to thrive on a carbohydrate diet. This adaptation was surely useful for opportunistic animals that were scavenging waste near ancient farming communities.
How they did it
Geneticists Erik Axelsson and his team at Sweden’s Uppsala University looked at DNA from gray wolves and domestic dogs, searching for small differences that might have shown up early in evolution as wolves transitioned to dogs. They zeroed in on specific mutations that dogs have and wolves don’t. In all, researchers found 36 genomic regions that reveal differences. Nineteen of those have to do with brain function, eight are related to the nervous system, and the rest are linked to starch digestion and fat metabolism, three of which carry instructions for making a protein that’s necessary for the digestion of starch. One is an enzyme that turns starch into sugar maltose. Another is an enzyme that turns maltose into glucose. And the third makes a protein that moves glucose from the gut into the bloodstream.
What does it mean?
If you think it answers the question as to why, where, and when dogs were domesticated, you’d be misinformed. It’s really more interesting than that.
1. Dogs eat more starch than wolves. The mutation explains why. Keep in mind that just because you have a mutation that lets you digest grain, it doesn’t mean, when given the opportunity, you wouldn’t rather have pork chops than cheerios. Just ask my dog, or my spouse for that matter. Wolves, dogs or proto-dogs (depending on your position) could have had the mutation long before humans planted grains. The study doesn’t suggest a time line.
2. Because all the breeds in the study have the mutation, the mutation occurred before these breeds radiated out from their direct ancestor. However, don’t assume that our modern breeds are representative of any dogs older than 500 years. There is a ginormous gap, at least 8 thousand years, between the ancient agrarian gang of dumpster diver dogs and the not-so-old proto dog that begat our modern breeds. Scientists don’t know if the missing link dog is extinct, and if she isn’t, they don’t know what living dogs would represent her. There’s plenty more work to be done.
3. The birth of agriculture impacted canids. But it did the same to humans, birds, insects, pigs, cows, and goats to name a few.
4. The study is a vindication for all the veterinarians who are treating dogs with kidney ailments as a consequence of the strange trend toward very expensive low-carb, raw meat diets. There’s a reason dog food is only 20- 30 % protein and 40 to 50% carbohydrates.
What others are saying
“Dogs are not just ‘tame wolves’ but have clearly adapted in a host of different ways to a very novel niche over a relatively short evolutionary timescale," said Adam Boyko, an expert on canine genetics and assistant professor of biomedical science at the Cornell University College of Veterinary Medicine and director of the Village Dog Diversity Project. “I think a lot of focus on dog domestication in the past centered on behavior and tameness. Clearly, they were important for domestication, but this paper also demonstrates genetic changes involved in diet adaptation.”
“The bigger question about the paper, said behavioral ecologist Ray Coppinger, is whether it sheds any light on the evolution of the dog -- whether they were domesticated "purposefully" by humans, or were they a result of humans creating a new niche which several species (including some Canis species) moved in and adapted to.” He added, “The researchers have done a great job showing that dogs and wolves genetically differ in their potential ability to digest starch. But it’s a fallacy to assume that the genes of the modern dogs included in the study are descended from original dogs. Thus the paper, sheds little light on the original dog, and does nothing to answer the question of artificial verses natural selection as the prime cause.”
What’s important about the study is not that it indicates when or where dogs originated. Rather, it’s a new tool that will help us understand how dogs and wolves are different. The research is groundbreaking, but it represents analysis of only 10 of the 36 genomic regions that the team identified. That means more exciting news is just around the corner.
Scholarly study takes on issues that are controversial. The dog origin debate continues to be particularly provocative. As for me, I just want to know who to thank.
Mark Derr, author of When the Dog Became the Dog has a very interesting post on this subject as well.
The genomic signature of dog domestication reveals adaptation to a starch-rich diet, Journal Nature, published on-line, January 23, 2013.