For some reason, human beings can't walk in a straight line. There's just something about our inner orientation that causes us to walk in a crooked or warped way. That's the conclusion of Robert Krulwich, science correspondent for NPR. In an interview on Morning Edition, Krulwich cites a study from Jan Souman, a scientist from Germany, who blindfolded his subjects and then asked them to walk for an hour in a straight line. Without exception, people couldn't do it. Of course everybody thinks they're walking in a straight line, until they remove the blindfolds and sees their crooked path.

Krulwich observed,

This tendency has been studied now for at least a century. We animated field tests from the 1920s, so you can literally see what happens to men who are blindfolded and told to walk across a field in a straight line, or swim across a lake in a straight line …, and they couldn't. In the animation, you see them going in these strange loop-de-loops in either direction. Apparently, there's a profound inability in humans to [walk] straight.

According to this research, there's only one way we can walk in a straight line: by focusing on something ahead of us—like a building, a landmark, or a mountain. If we can fix our eyes on something ahead of us, we can make ourselves avoid our normal crooked course. Kurlwich concludes, "Without external cues, there's apparently something in us that makes us turn [from a straight path]."