We have two dogs, our big thirty-kilogram galumphing galoot, Guinness:
Carol and I frequently laugh ruefully at how many times a day we say, "They are so stinkin' cute." I mean, it's true, but it's kind of ridiculous how much they have us wrapped around their paws. Guinness, especially, has an incredibly expressive face, and when we talk to him he gazes up at us adoringly as if he's hanging on every word we say. The funny thing is that it doesn't, in fact, matter what exactly it is we're saying. We could be explaining to him something like why it is not a good idea to eat the sofa, or reading to him from a text on economics for that matter, and he will still stare at us as if to say, "My god, yes! That's genius! I never would have thought of that!"
A paper presented last week at the annual meeting of the American Association for Anatomy has shown that this ability dogs have to communicate with their facial expressions is no accident. Researchers Anne Burrows and Kailey Omstead of Duquesne University did a detailed comparison of mimetic muscles -- the tiny muscles in the face that allows us (and other animals) to alter our expressions -- between domestic dogs and wolves, and they found something fascinating.
To understand what's going on here you have to know a little about muscle composition. In the broadest-brush terms, mammals have two types of skeletal muscles; fast-twitch muscles, which can contract rapidly and powerfully but aren't able to maintain sustained contraction, and slow-twitch muscles, which are much slower to react but can remain contracted for long periods. Our upper bodies are predominantly fast-twitch muscle; this is why lifting a heavy weight with your arms is doable, but keeping it lifted for more than a few minutes is excruciatingly difficult. On the other hand, the three big muscle groups in your upper legs -- the quadriceps, biceps femoris (hamstrings), and gluteus maximus -- have to maintain tension just to allow you to support your own body weight, but can do so for hours without fatiguing. One of the reasons for this is that slow-twitch muscles have a protein called myoglobin, which improves the ability of the muscle to absorb oxygen from the blood; it's this protein that makes the dark meat of a chicken dark. And notice which two muscles are dark meat -- the leg and the thigh, same as us.
Not that I'm recommending eating humans, mind you.
Anyhow, back to dogs. The analysis by Burrows and Omstead found a striking difference in the muscle composition of dogs' faces as compared to wild wolves; dogs' mimetic muscles are predominantly fast-twitch, while wolves' are predominantly slow-twitch. What this means is that dogs' faces are much quicker to change in expression. Wolves do have expressions; one obvious example is the wrinkled forehead and retracted lip that signifies aggression or anger. But domestic dogs can alter their expressions rapidly and subtly in response to the circumstances, allowing them to communicate with humans in a way few other animals can."Dogs are unique from other mammals in their reciprocated bond with humans which can be demonstrated though mutual gaze, something we do not observe between humans and other domesticated mammals such as horses or cats," said study co-author Anne Burrows. "Our preliminary findings provide a deeper understanding of the role facial expressions play in dog-human interactions and communication."
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