Hounds, pointers, and other dogs bred for their excellent abilities to pick up a scent tend to have longer snouts—but it’s not just that a bigger nose is a better one. Researchers have found that human domestication of dogs has shifted the structure and alignment of some dogs’ brains. And in those varieties with shorter snouts—which humans bred for other reasons, like appearance—the olfactory brain region rotated to a different part of their skull, leaving scientists to question whether we’ve crossed up their smelling abilities (and perhaps more).
Since the first wolf was domesticated an estimated 12,000 years ago, “selective breeding has produced a lot of [anatomical] variation, but probably the most dramatic is in terms of skull shape,” said study co-author Michael Valenzuela [National Geographic].
For this study, which appears in the open-access journal PLoS One, Valenzuela and colleagues examined the brains of 11 dog breeds and found great variation in the size and shape of their skulls. The breeds with shorter snouts had brains that rotated forward by as much as 15 degrees over the generations, the scientists say. That means that the olfactory lobe, as well as other parts of these dogs‘ brains, has shifted position and shape because humans guided their evolution through domestication.
Valenzuela says that in particular humans might have altered the dogs’ rostral migratory stream, or RMS, a connection in the brain that’s important for the sense of smell.
“The RMS starts very deep in the middle of the brain and traces a very predictable path to the olfactory bulb…. Since the olfactory bulb has moved in brachycephalic [short-snouted] dogs, you’d expect to see a change in the course of the RMS, or it may be disregulated” [National Geographic].
The researchers don’t know yet how much the brain changes affect the dogs and their world of smell. But they say the differences in brain size are another surprise showing how diverse dogs can be.
As Dr. Valanzuela explains, the most astounding thing is that dogs’ brains can actually handle such huge differences in the shapes of the skulls that house them. Dogs have already shown unprecedented levels of variety in their different physical breeds, but the variation in brain organization is an even more fundamental and thus more incredible form of diversity across the species [io9].
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Image: Wikimedia Commons