William Wells in Seed Magazine:
Negative campaigning plays off deep-rooted pathways in the human brain, which may explain its effectiveness as a tactic and its lure to politicians. Humans evolved to remember negative events not because they faced electoral choices but because they faced possible death. For example, “it matters exactly what the snake looks like — if you see it again, you can respond,” says Elizabeth Kensinger, a neuroscientist at Boston College who studies the strength of negative memories. “There is this threat to survival from negative emotions. What the chocolate cake looks like is not going to be so important.”
Negative campaigning, at its simplest, is an attempt to exploit this evolutionary response and make a strong impression on a distracted voting public. Indeed, in Kensinger's controlled laboratory experiments, negative words create the strongest memories. “When things are negative is when people feel that they vividly remember the experience in a really crisp way,” she says. Katherine Kinzler of the University of Chicago has found that negativity also gets priority when remembering faces and actions. She thinks the responses are hardwired by evolution rather than learned via culture, because the phenomena are present even in infants. An ancient origin is further suggested by brain studies: Fear and negativity light up the amygdala, a primeval part of the brain.
But how, if at all, does the negative-memory bias apply to political campaigns?