Why linearity is not enough

Organic chemists dearly love linearity. Nothing is more linear and causal than a multistep synthesis. We always search for conditions producing just what we want in high yield with as few unwanted products as possible, thank you very much. Le Chatelier’s principle is used again and again to force reactions to go just the way we want. It is a type of thinking that will not help us understand what is going on within our cells.

It all has to do with feedback.  The following is from an old post of mine on “The Skeptical Chymist”.  Its purpose is to lay the groundwork for the next post and the one after that.  The following example is on the organismal level.

Endocrinology was pretty simple in med school back in the 60s. All the target endocrine glands (ovary, adrenal, thyroid, etc.) were controlled by the pituitary; a gland about the size of a marble sitting an inch or so directly behind the bridge of your nose. The pituitary released a variety of hormones into the blood (one or more for each target gland) telling the target glands to secrete, and secrete they did. That’s why the pituitary was called the master gland back then.  The master gland ruled.

Things became a bit more complicated when it was found that a small (4 grams or so out of 1500) part of the brain called the hypothalamus sitting just above the pituitary was really in control, telling the pituitary what and when to secrete. Subsequently it was found that the hormones secreted by the target glands (thyroid, ovary, etc.) were getting into the hypothalamus and altering its effects on the pituitary. Estrogen is one example. Any notion of simple control vanished into an ambiguous miasma of setpoints, influences and equilibria. Goodbye linearity and simple notions of causation.

As soon as feedback (or simultaneous influence) enters the picture it becomes like the three body problem in physics, where 3 objects influence each other’s motion at the same time by the gravitational force. As John Gribbin (former science writer at Natureand now prolific author) said in his book ‘Deep Simplicity’, “It’s important to appreciate, though, that the lack of solutions to the three-body problem is not caused by our human deficiencies as mathematicians; it is built into the laws of mathematics.” The physics problem is actually much easier than endocrinology, because we know the exact strength and form of the gravitational force.

Causality is inherently a linear, sequential idea.  Even chaos theory is basically causal (deterministic), although predictability goes out the window.

The next post will show just how chemistry and linearity are necessary but not sufficient to understand what’s going on in the cell (among other things).