After returning home from a trip, work or even a short walk to take out the garbage, dog owners are routinely greeted with copious amounts of drool and tail wagging. But why? As George Dvorsky explains over at io9,  the answer is in dogs' brains — and even their DNA.

Some of dogs' enthusiasm comes down to their wolf ancestry. Wolves often greet each other with face licking—a way of affirming social bonds and checking out what your buddy caught on a hunt. That said, wolves are more skeptical of new things, so dog greetings are much more exaggerated. Some argue that the most social wolves would have been the ones domesticated by humans 10,000 to 15,000 years ago, explains Dvorsky.

There's another component to goofy dog greetings: the brain. Dogs can distinguish human smells from those of canines and recognize familiar odors, writes Dvorsky in a deep dive that's well worth checking out. Brain imaging studies also suggest that the sight of an owner switches on pathways in the brain associated with reward. (The same thing happens when humans see friends.)

All of those explanations could certainly be behind the plethora of YouTube videos of dogs going nuts at the sight of owners returning home:

There’s also some recent evidence that dogs and humans share a unique bond. When they gaze into each other’s eyes, their brains secrete the hormone oxytocin. It’s linked to social bonding in several species, but most notably between human mothers and babies. Even when raised by humans, wolves do not experience the same oxytocin rush.

Obviously, all dogs are different, and greetings definitely vary. Dogs who aren’t used to being separated from their owner may be more enthusiastic when that long-lost owner returns (even if it's only been a few minutes). Either way, it’s clear that dogs can get as much enjoyment out of seeing their human as their human gets out of seeing them.

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