Scientists Found a Paradox in Evolution—and It May Become the Next Rule of Biology

It may have fewer than many of the other sciences, but biology does have two dozen or so “rules”—broad generalizations about the behavior or nature and evolution.
Now, USC researchers want to add a new rule called “selectively advantageous instability (SAI),” which explores how instability can actually benefit a cell and a cellular organism.
The flipside of this “rule” is that SAI can also be a key factor to things like disease and aging, so understanding this process could aid in exploration of those biological processes.

Across the sciences, rules and laws help us make sense of the world around us, whether applied to cosmic scales or subatomic ones. However, in the biological world, things are a bit more complicated. That’s because nature is often full of biological exceptions, and so “rules of biology” are also considered broad generalizations rather than absolute facts that explain and govern all known life.

Some of these broad generalizations include things like Allen’s Law, which dictates that body shapes in endotherms (warm-blooded animals) adapt to climatic conditions—short and stocky helps retain heat in cold climates, while tall and lanky helps dissipate heat in warmer ones. Another “law,” known as Bergmann’s rule, states that species of a broadly distributed clade tend to be larger in colder climates and smaller in warmer ones (though of course, as with most biological rules, exceptions apply).

Some two dozen or so rules currently exist that describe all kinds of processes of the natural world, and now, researchers as the University of Southern California (USC) hope to add a new rule. At first glance, this new rule—called “selectively advantageous instability,” or SAI—seems to defy the underpinning assumptions of life in general, and pushes against the current assumption that life craves stability and a conservation of resources.

While nature does tend toward stability (it’s one reason why we see so many hexagonal shapes in the wild, including honeycombs and insect eyes), USC molecular biologist John Towers argues that instability in biological components like proteins and genes can actually be helpful to cells. The study was published last week in the journal Frontiers in Aging.

“Even the simplest cells contain proteases and nucleases and regularly degrade and replace their proteins and RNAs, indicating that SAI is essential for life,” Tower said in a press statement. “This can favor the maintenance of both a normal gene and a gene mutation in the same cell population, if the normal gene is favorable in one cell state and the gene mutation is favorable in the other cell state.”

These states allow for greater genetic diversity, which in turn can make organisms more adaptable. Many cell components also favor a short lifespan, as this actually helps promote cell health. This indicates that SAI in these components is a necessary biological function.

Of course, there are plenty of downsides to instability. This energy-requiring process of mutation instability can introduce deleterious cells that contribute to aging, while also inducing other types of damage and dysfunction.

“Aging has proven to be difficult to define, but most definitions include an increased chance of death with age, and decreased reproductive fitness with age,” the paper reads. “SAI can create a cost for the replicator in terms of energy and/or materials, and this cost might be interpreted in terms of promoting aging.”

Another piece of evidence supporting SAI’s ubiquity and its candidacy as a new “rule of biology” is that it crops up in other well-known concepts, including chaos theory and ideas of “cellular consciousness.” Because of this—as well as its links to fundamental biological processes like aging—understanding the inner workings of SAI could help biologists explore cellular life in a whole new way.