We know that human have been practicing deliberately selective breeding of plants and animals for thousands of years. It seems pretty clear that less purposeful selective breeding has been going on from the dawn of agriculture, or perhaps before. Christopher Boehm suggests that one of the earliest targets of our selective breeding could have been our own species.
How could this work? Well we know that many contemporary societies, and essentially all hunter-gatherers deal with anti-social behavior by a whole range of techniques, including gossip, social pressure and ultimately banishment or even homicide. The latter would seem to be rather strongly selective against tendencies towards these kinds of behaviors.