Not too long ago, dogs were mainly valued for the work they did. They helped hunt for food, herded livestock and guarded homes. To do these jobs, dogs needed to have strong instincts to chase prey, a lot of energy, and a healthy suspicion of strangers. Just a few decades ago, many dogs were expected to bark at any noise, keeping watch over their owners and homes. Their instincts kept away squirrels from bird feeders and burned off some of their excess energy.

However, in just one generat...