Neoteny

One of the interesting ideas in my dog books is the concept of neoteny, or the retention of juvenile characteristics, as a common feature of almost all breeds of domesticated dogs (see this article). When you look at dogs in light of this, you really do see the "puppy-like" traits and behaviors.

One of the references used in a couple of the books concerns a 40-year experiment in domesticating Siberian Foxes to simplify their care in (originally) Soviet fur farms. After a just a few generations of selecting for tameness, the foxes underwent a number of seemingly unrelated physical and behavioral changes. They developed shorter snouts and floppy ears-- common to many canid puppies-- and multicolored fur, which undermined their value in the fur trade. They also took to barking, wagging their tails, and whining for joy at seeing a friendly face, which are behaviors unknown in wild foxes. They were just trying to make a less freaky fox, and they reinvented the dog in a person's lifetime.

There's a bit more about the study here.