In particular, dogs show changes in genes governing three key steps in the digestion of starch. The first is the breakdown of large carbohydrate molecules into smaller pieces; the second is the chopping of those pieces into sugar molecules; the third is the absorption of those molecules in the intestine.
“It is such a strong signal that it makes us convinced that being able to digest starch efficiently was crucial to dogs. It must have been something that determined whether you were a successful dog or not,” Axelsson said.
The change is at least partly the consequence of dogs having multiple copies of a gene for amylase, an enzyme made by the pancreas that is involved in the first step of starch digestion. Wolves have two copies; dogs have four to 30.
As it happens, amylase “gene duplication” is also a feature of human evolution. Humans carry more copies of the amylase gene than their primate ancestors. People also produce the enzyme in saliva, which allows the first steps of digestion to occur while food is still in the mouth. That, in turn, rewards chewing and increases the palatability of food.
In dogs, however, the increased amylase activity occurs only in the pancreas. The enzyme isn’t at work in their mouths, probably because the food doesn’t stay there long enough. Dogs may be able to eat human food, but they still wolf it down.
The researchers found 19 genome regions containing nervous system genes that are significantly different between wolves and dogs. Eight regions contain genes governing brain development.
How those genetic mutations explain dog behavior is a topic of future research. However, the fact that so many are involved in brain maturation supports the theory that dogs are really wolves that never grew up.
Sociability around strangers, curiosity and playfulness are traits seen in both wolf pups and dog pups. So are floppy ears, broader faces and liberal tail-wagging. They all persist in adult dogs but are largely extinguished in adult wolves.
This retention of juvenile traits into adulthood — a phenomenon known as “neoteny” — is a key feature of domestication, some biologists believe. In a famous four-decade, 40-generation experiment in Russia, these traits emerged in foxes when scientists selectively bred the animals for tameness.
But the process may not require human intervention. Similar behavior probably evolved naturally in dogs. The willingness to wander fearlessly among people is a big plus if scavenging human food is your business (as it still is for millions of “village dogs” around the world).
There’s a theory that this “self-domestication” also happened in the evolution of Homo sapiens.
As people created permanent settlements — and running away from those you didn’t like (or killing them) became less of an option — there may have been a survival advantage to being cooperative and self-controlled. It’s possible that studying the genes that determine dog sociability might shed light on how a less aggressive, more civilized human evolved, Axelsson said.
It would also help explain why dog is man’s best friend. They grew up together.