Why all the bitter, negative political ads?

They work. So, the question should be, "Why do negative political ads work?" To simplify the answer, it is because our brains retain bad news longer than good news.

Scientists have proven this in numerous ways. Here is a simplification: Show subjects a series of pictures on a TV monitor - like a slide show. The pictures cover all sorts of things: good, bad and indifferent visuals. Then the subjects are shown a second set of pictures, and given a handheld device which they are instructed to click every time they recall that a picture in the second batch also appeared in the first batch. It is a test of which kinds of pictures they recall accurately.

The same is done with audio. Short, abstract sentences read by an announcer. After listening to the first batch of readings, they are asked to listen to a second batch and note each time they hear a sentence which was also in the first group of readings.

In every test, people remember the "bad" stuff much better than the "good" or "neutral" stuff.

I believe the reason is an ancient one, alive and well in our modern brains. Suppose you are an ancient person, a hunter-gatherer, doing your daily round of hunting and gathering food for the day. You see a wide variety of nature's creations. Then, suddenly you discover that a sabre-toothed tiger occupies a certain valley. You may well forget the meadow where you saw a mouse; but you are not going to forget that valley of the tiger.

It may have started by our remembering more accurately those things which were a danger to us. But it isn't limited to that. On the front page of today's local newspaper, there is a story of a small child who was killed in an auto mishap. To be specific, some family member backed a pickup truck over the child. A horrible accident. I read every story on that front page, but that is the only one I now recall. Somehow bad news, even when it happens to someone we do not know, is remembered longest.

This does not mean that the dirtiest, meanest political ads will always get their candidate elected. As in other types of advertising, some political ads are just poorly done. If an attack ad seems implausible, frivolous or just unfair, it may backfire. But it will almost certainly be remembered. And for that reason, people who write political ads will always search for a way to vilify their candidate's opponent.