A Mystery: Why Can’t We Walk Straight?

More like building a mystery*. Perhaps I am missing something, but I’m having a hard time understanding the “mystery” behind this. From a physics standpoint, we know that a moving object will travel at constant speed in a straight line if and only if there is no net force acting on it. Forces along that path will change the speed, so we don’t have to worry about that, and vertical forces can be ignored, since we aren’t going to start levitating or submersing ourselves in the ground. Which leaves us with the last component, which is perpendicular to the path. An acceleration perpendicular to the path gives you — ta da — circular motion. Physics 101.

I’m guessing the problem is in the assumption that the human brain could remove all biases in our locomotion and produce only forces along the direction of travel, without visual cues for feedback. Why would you assume that to be true? The surprise might be that there are biases rather than fluctuations, which would lead to a random walk (in the perpendicular component), but that’s still not a straight line. Assuming no noise processes at all is just naive.

*no data on if this effect holds while wearing sandals in the snow