According to Berns’ research, dogs that are presented with certain smells in scanners can clearly tell the difference between dogs and humans, and also discern and recognize familiar and strange odors. In particular, the scent of a familiar human evokes a reward response in the brain.

“No other scent did that, not even that of a familiar dog,” Berns told io9. “It’s not the case that they see us as ‘part of their pack as dogs,’ they know that we’re something different— there’s a special place in the brain just for us.”

Berns stresses that dogs are social with us not just because of their scavenging tendencies.

“What we’re finding with the imaging work is that dogs love their humans—and not just for food,” he says. “They love the company of humans simply for its own sake.”

http://io9.com/why-are-dogs-so-insanely-happy-to-see-us-when-we-get-ho-1721329341