Above the eyes

Catalyst: Pet Subjects - Dog eyebrows - ABC TV Science

I found this segment on Catalyst this week pretty fascinating. The key to feeling that we can understand dogs, it suggests, is because they are one of the few animals with expressive eyebrows. This is in contrast to cats (and, I would think, horses.)

Now if you look at the equivalent muscle in the cat, it's not strong, and attaches all the way across the eye ridge. Which means the cat can't do much interesting with that muscle. Whereas the dog's levator anguli oculi medialis is perfectly placed to raise just one edge of its eyebrow. But the deeper why question is, why do dogs have this special eyebrow muscle, and most animals don't? Well the best theory concerns the evolution of social living. In general, the most social animals have the most expressive faces.

One study showed foxes who hunt alone had about half the facial expressions of wolves who work in packs. In fact, in wolves and dingoes, the eyebrows are often even a different colour, exaggerating the movement.

Sounds a plausible theory.