A study has shown that dogs have become more intelligent, and even developed a sense of right and wrong, through spending time with humans.

Because of the way owners have selected smarter and more empathic dogs over generations, these pets now appear to have a limited capacity to understand the desires, motivations and intentions of others.

A decade ago, most scientists would have dismissed the claims of dog owners that their precious pets could "human emotions". Now that dismissive view has been challenged by a remarkable experiment to probe canine cognition. Researchers put dogs through a classic experiment normally done with children, in which an instructor demonstrates to a toddler how to turn off a light using her forehead, once with her hands clearly visible and once when wrapped in a shawl, so that she can't use them. When invited to turn the light off for themselves, toddlers who were shown the first version use their heads, but those shown the second use their hands.

The standard interpretation is that the first group conclude that there must be a good but non-obvious reason for using the forehead method, as otherwise the instructor would have used her hands. As it turns out, dogs do the same thing, demonstrating that they have developed empathy.

Others have argued that since rough-and-tumble dog play rarely escalates into full-blown fighting, the animals must abide by rules and expect others to do the same. In other words, they know right from wrong.