【英语时差8,16】为何狗要咆哮（下）（在线收听）

Now, a few tens of thousands of years ago, wolves and people started becoming friendly species. You can imagine a person tossing a bone to a friendly wolf from time to time. But “friendly” is the key. Nobody ever gets close to a hostile wolf. So over many thousands of years we would have been gradually selecting for certain behavioral traits–playfulness, low hostility, the ability to bond. Very puppy-like behaviors! See what’s happening? A species that resembles a wolf puppy that never grows up may have slowly evolved in this way. That species would retain its puppy-like behaviors, such as barking, but never grow into growling, howling adult wolves. That species We would now call that species “dogs.”