Wuzu Fayan said, “It is like an Ox that passes through a latticed window. Its head, horns, and four legs all pass through. So, why can’t its tail also pass through?”

There’s always a catch. Even if we manage, by some combination of skill and grace, to pass our great head and body through the window, we can feel our little tail caught in the lattice. Tugging only wedges it in more deeply. Is this a design issue? Is something fundamentally wrong with the window? With us oxen? Or with our encounter?

Sometimes being caught in the world is not a problem, even if it is a mistake. Indeed the ancient furnace of natural selection, whereby new organic forms are forged, is stoked on mistakes. To consider how error is key to generating new life, consider something smaller than an ox, consider a bug. Thanks to natural selection, there are lots to choose from. I’m seeing a cockroach.

Bugs All the Way Down. The tale is told that the origin of the use of the term “bug” to indicate a computer coding error lies in an actual insect flash-fried in the circuitry of an early mainframe. The bug caused the great beast to crash. Both coding- and crawling-type bugs can cause computer malfunction, but they are distinct: one’s in software, the other in hardware.

Separating coding errors into two types, software or hardware, gets subtle when investigating living organisms, such as bugs! With creatures, errors may also arise in the software (DNA or genotype), or in the hardware (body or phenotype). However, in living systems the software of one generation will affect the hardware of the next generation down the evolutionary stream. (If your laptop did that, and was able to reproduce, an app could be run that might cause the computer’s offspring to very slightly shrink.) Furthermore, unlike those of objects, the genotype and phenotype of a living system are entwined in an intimate tango of cause and effect—neither partner wholly leading.

And while it is usually clear when a technological coding error has occurred (the result is not what I, the programmer, intended, and I don’t like it), in living systems there is no programmer standing behind the code with an intention. What then announces that an error has occurred? Almost always the body itself: bad code results in a body that does not fully thrive, a body less well fitted to its environment. Often enough, the coding error will ultimately produce a body whose goal, the ability to reproduce, is impaired. That’s the last mistake that code will ever make.

But sometimes not. Sometimes the tail that is caught turns out to be the way through.

The dharma without error is not the living dharma. Anyone who happens to be alive as they are reading this comes from an ancient lineage exuberant with error. In this lineage perfection is deadly. Indeed the process of natural selection depends upon a level of so-called “random variation” (error!) in the genetic code. These errors then produce variants in the body and behavior of the creature, relative to those without the genetic variation. Again, these bodily variations usually cause a decrease in fitness, which is why the word “mutation” normally brings to mind something along the lines of Frankenstein’s monster. But occasionally the body gains a new advantage and the mutation increases fitness! This error now provides a gateway to a land of new and better embodiment – mistakes as Moses. The embodied novelty provided by these “errors/improvements” produces selective pressure, as creatures can explore new fitness opportunities afforded by these mutations. Again, there’s no “push” or intention toward increasing the diversity of forms. In fact a great deal of biochemical structure goes into making the copying process error-free, to guarantee that the DNA changes not one iota. But tiny errors still occur, and new tiny tails get caught. Though rare, these beneficial mutations provide the necessary stage for the next lucky mistake, and this feedback is iterated an enormous number of times over billions of years until a biosphere of such diversity emerges that a creature turns up able to furrow her brow about it all.

Thus oxen, cockroaches, and Zen practitioners each emerge, wandering like pilgrims, from an original single-celled mother through a compounding transformative cascade of marvelous errors. Of course, no individual pilgrim survives in this immense goalless journey, and yet this ecological immensity is constituted by these small impermanent paths. And if here and there life seems a tight or uninspired fit, help is arriving every moment: new tails affording the opportunity to be caught in marvelous new ways.

• The title of this piece refers to a refrain in a wonderful poem by Antonio Machado, “Last Night as I Lay Sleeping”. So wonderful, in fact, that you should just stop reading this and go read the poem. Here’s one stanza:
  
  “Last night as I was sleeping
  
I dreamt—marvelous error!—
  
that I had a beehive

  here inside my heart.
  
And the golden bees

  were making white combs
  
and sweet honey
  
from my old failures.”