Taking the Appropriate Steps

Stairs are a tricky business. When you start climbing a set of stairs, it only takes your body 2 or 3 steps to “learn” how far it is from one to the next. The spacing is quickly adapted to, which is why, I suppose, OSHA has a limit of 1/4” of variation in riser height. A small but sudden departure from evenly spaced treads can be a significant hazard and contributor to falls. Anyone who has mistakenly believed that there was one more or one less step has had a kind of near-death experience related to this phenomenon.

Obviously, it isn’t that we need perfectly flat ground or perfectly even stairs to survive in the natural world. We got along fine with the natural terrain of rocks and riverbanks and slopes for a long time before stairs or escalators were developed; we simply had to pay attention and exert ourselves. It’s that a regular pattern is easy to identify and our body quickly figures out how to put itself on auto-pilot for efficiency: there’s no benefit to investing extra effort where it isn’t obviously needed.

We fall when we mistakenly perceive the steps to be even and they are instead off by more than 1/4” or so. For our safety, the distinction must be as sharp and obvious as going from one stair tread to the next: the path must either be noticeably irregular and unpredictable or utterly monotonous. But for our humanity—our animal agency—we need uneven terrain to engage our senses and challenge our balance.

P.S. Cats instinctively know that we are most vulnerable when we are carrying a basket full of laundry on the stairs and frequently make attempts to assassinate us there by suddenly appearing underfoot.