Dog's are fairly closely related to wild dogs and and wolves which are not known to bark. It is theorized that dogs have actually evolved for their owners.
They have developed two very distinct barks: an alarm bark and a playful bark. This is another kind of adaptation due to the fact that most wolves do not have a playful characteristic trait and therefore would have no need for a playful bark.
These adaptations developed as dogs became more loyal to their owners. As dogs changed from their primitive instincts to being more loyal and bonded, they developed a new way to warn and protect their owners.
This is an example of modern adaptation because wild dogs and wolves are not accustomed to being playful and will rarely bark. But, as dog's have evolved to have an emotional connect with humans, their personality traits have also evolved. Also, since dogs are only 50,000 years removed from their counterparts, we can assume that this adaptation developed recently.