They hunt, live and raise their young cooperatively. When living with people, they transfer that sociability to us. This transfer leads to the communication we value so highly. He's my best friend. It's because he adopts us into his world as much as we adopt him into ours.
Dogs are truly a genetic miracle, the most varied species on the planet.
Regardless of whether they are 2 pounds or 200, they all have the same motivations, instincts and needs. There is no democracy in dogdom. They fit every interaction into one of these two psychological categories. When your dog comes up, drops a toy on your lap and barks at you, he is being dominant. He is commanding you, nicely, to throw it.