Reprinted from Slate with permission of the author.

What is wrong with David Letterman's heart? The official reason for his quintuple bypass last month was atherosclerosis--clogged arteries. Some observers, such as People magazine, go deeper in search of the explanation, citing "Type A," workaholic behavior. But I submit--with the support of actual scientific evidence--that what's wrong with Letterman's heart is the same thing that is wrong with his TV show: excessive cynicism.

The classic Type A patient, as defined decades ago, was impatient, ambitious, and volatile, the kind of guy who would go berserk if a traffic jam made him late for a power lunch. As it turns out, the link between classic Type A behavior and heart disease is pretty flimsy (as James Gleick entertainingly shows in his recent book "Faster").

Still, as researchers picked apart the Type A personality, they did find one of its elements to be firmly correlated with heart disease. On the Minnesota Multiphasic Personality Inventory, this element is called "hostility." But, as Dr. Redford B. Williams wrote years ago in The Sciences magazine, what the MMPI hostility scale actually measures goes beyond hostility; it is closer to the dictionary definition of cynicism: "a contemptuous distrust of human nature and motives."

Here are some items on the MMPI hostility scale: "I think most people would lie to get ahead"; "Most people make friends because friends are likely to be useful to them"; "A large number of people are guilty of bad sexual conduct." Right there you have the worldview underlying at least half of Letterman's jokes.

Of course, you also have the worldview underlying half of Jay Leno's jokes (and for that matter, you also have a largely accurate worldview--but that's another matter). Still, there's a difference between Leno and Letterman. Leno doesn't meet the full definition of cynicism--"a contemptuous distrust "--because he lacks the contempt. He's not a fundamentally hostile person--at least, he doesn't come off that way on television. With Letterman, contempt for his guests is often palpable.

Sometimes the problem seems to be insecurity. Letterman is so fearful of failure that at the slightest lull in the show, he may expose a guest to any form of meanness that could get a laugh. Then again, insecurity and hostility are pretty much two sides of the same coin to begin with. (A few years ago, after erstwhile Letterman groupie Tom Shales of the Washington Post started saying critical things, Letterman did a skit making fun of Shales for being overweight. Ha, ha.)

There has been some improvement lately. Letterman often seems to work at being kinder and gentler to guests. The problem is that it's such obviously hard work. True change comes from within.

Still, there's real cause for hope. Letterman's show has seen a slight ratings upturn this season after some format changes. And, though he suffers under the burden of CBS's weak prime-time lead-in, he does have the advantage of being, unlike Leno, a truly creative comic mind. Maybe all he needs is the sort of genuine softening of outlook that quintuple bypasses and other brushes with death have been known to induce.

I say all of this as a fellow cynic, and a fairly hostile one. Like Letterman, I've long needed to turn my jaundiced view of humankind into a detached bemusement, a more lighthearted absurdism. And, like Letterman, I haven't succeeded...Maybe I'll take Letterman's story to heart. Maybe I can change. But I doubt it. People are rotten to the core.