The descent of American presidents from George Washington to Ulysses S. Grant, argued the 19th century writer Henry Adams, was enough to raise doubts about the theory of evolution. Anyone looking to debunk Darwin today could find ample evidence in the behavior of travelers going through airport security every day.

More than 13 years after 9/11 brought a fresh set of rules for air travelers, most of us have gotten used to everything now demanded as we go through checkpoints: liquids in small bottles stashed in a plastic bag, shoes and coats off, laptops out, metal in bins.

By now, the process should be a rote drill. But if you can do all this without much trouble, you’re one of the smart ones. As you’re pulling your cellphone and keys out of your pockets, the person behind you may be blithely toting a pistol, a stun gun or a hand grenade.

In 2014, the Transportation Security Administration said in its latest annual report, 2,212 firearms were intercepted at the nation’s checkpoints, or six a day. Not to worry: Only 83 percent of them were loaded. That’s up from 1,813 the year before. In fact, the number has risen every year since 2005, when the total of confiscated guns was just 660 — less than a third of the latest number.

The weapons were found at 224 airports.

TSA says the people who pack heat typically lack bad intentions. “The most common excuse people give when we detect a firearm in their carry-on bag is that they forgot,” a TSA representative told ABC News. “The second most common excuse is that their husband or wife packed the bag.”

That’s a relief. But seriously: How do you forget you have a loaded .380-caliber handgun strapped to your ankle? Seems like it would be easier to forget your pants.

Firearms are not the only things that really get TSA’s attention. Stun guns also turn up pretty often. One traveler brought a live hand grenade to Los Angeles International, forcing a checkpoint to be closed, a bomb squad to be dispatched and several flights to be delayed.

Some of those caught would have trouble claiming absent-mindedness: Screeners found a razor blade secreted in a cellphone, a stun gun disguised as a lipstick, a saw blade hidden in a Bible, an “improvised explosives device training kit” and an 8-inch knife wrapped in an enchilada.

So apparently the traveling public includes two distinct types of boneheads: those who can’t remember putting a pistol in a back pocket, and those who think a tortilla can foil an X-ray machine.

We can only hope the terrorists are half as dim.

Editorial by the Chicago Tribune