The hallmark behavioral difference between domesticated animals and their wild contemporaries is a lower threshold of reaction to external stimuli and an overall reduced wariness of other species—including Homo sapiens. The likelihood that such traits are in part a “domus effect” rather than entirely due to conscious human selection is, once again, suggested by the fact that uninvited commensals such as statuary pigeons, rats, mice, and sparrows exhibit much the same reduced wariness and reactivity. [James C Scott, Against the Grain]
Domesticated cows are hard to startle. But so are city pigeons. So the cows might have developed their calmness not as a result of deliberate selective breeding, but through the evolutionary effects of sharing habitat with humans.
Change the habitat, change the behaviour. You don’t necessarily need to breed or train waway fear and aggression – just create a situation where they are not useful.
Scott is primarily talking in evolutionary timescales, but the same applies within a lifetime. And it applies to humans as well as to animals.
We are constantly being trained by our habitat. The commuter has been conditioned to stand inches away from his fellow-travellers, just like the Wild West gunslinger who never sits with his back to the door has been conditioned. No need to explicitly train attitudes to personal space, just make the Tube the easiest route to work.
There’s an obvious self-directed extension of this. When you want to change your own behaviour, perhaps don’t attempt to train yourself directly. Instead set up an environment which encourages the desired behaviour, and let the environment do the training.