The Lichen Rule

…a thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise —Aldo Leopold

Preamble Everybody knows the Golden Rule – Do unto others as you would have others do unto you – but who ever heard of the Lichen Rule?

First Approximation


he Golden Rule of course asks us to behave equitably toward one another. It exhorts us to act with mutual respect and moral reciprocity. Again, Do unto others as you would have others do unto you. How could you possibly go wrong?

And yet, it takes more than the Golden Rule to make a world go round, or even a society. The reason is this: that doing unto others as you’d have them do unto you works well horizontally, from person to person, but breaks down in larger, more hierarchical social structures, as from ruler, say, to ruled.

Rhizocarpon geographicum by Jason Hollinger

In these larger groups, the Golden Rule must necessarily yield to a principle of vertical reciprocity – a principle that governs not just the relation of individual to individual, but the relation of the individual to the group taken as a whole, and vice versa, call it the relation of the parts to the whole and the whole to the parts.

Actually, it was just such a principle of vertical reciprocity that Thomas Hobbes elaborated in his 1651 book Leviathan – the idea that governance must take its authority from an arrangement of mutual responsibility between ruler and ruled. About a century later, Jean-Jacque Rousseau dubbed this principle the social contract, according to which people agree to yield certain rights and freedoms to the state in exchange for protection of other rights and freedoms.

Much has been written about the social contract since then, though it’s often forgotten that humans didn’t invent the concept out of thin air. On the contrary, the principle of vertical reciprocity has been operational almost from the beginning, inscribed by evolution into all enduring relational systems across the Living World, from social interactions in ants and antelopes to the internal functioning of your own body: always there’s a necessary reciprocity between the parts and the whole.

Formulated broadly, and in my own idiosyncratic reading, the principle of vertical reciprocity states that relational systems are durable only to the extent that the parts refer themselves to the needs of the whole while the whole in turn confers resilience on the parts – a worthy candidate for an ecosystemic law that qualifies also, again in my reading, as a Gaian Axiom.

Now as it happens, this principle likely finds its purest, highest, most archetypal expression in a group of organisms dear to my heart, the lichens. Not all lichens equally, mind you, but above all the Lecanorolichens which, without getting lost in the weeds, just happen to be the only lichens you’ll probably ever notice.

Lichens, all lichens, recall, are enduring, the physical emergent outcomes of, at minimum, a fungus and an alga/cyanobacterium living in long and intimate association. Said another way, any lichen you hold in your hand consists of two organisms growing together that at the same time produce a third organism, namely the lichen itself. And it’s in the relationship between the parts and the whole of the lichen that the principle of vertical reciprocity comes into play.

OK, so what sets the Lecanorolichens apart from most other lichens is their remarkable evolutionary stability as lichens. Unlike the fungal partners of most other lichens, which tend to move in and out of the lichenized condition across evolutionary time, the fungal partners of Lecanorolichens remain, from beginning to end, and with very few exceptions, lichenized: the purest, highest, most archetypal expression of what must surely be termed the Lichen Rule.

To recap, the Lichen Rule is the principle of reciprocity viewed from the top down. As in the latter case, so in the former: relational systems are durable only to the extent that the parts refer themselves to the needs of the whole while the whole in turn confers resilience on the parts.

All well and good, but what does this actually mean? What does it mean that Lecanorolichens are the perfect embodiment of the Lichen Rule? Well, for one thing it means that Lecanorolichens don’t handle environmental perturbation very well; that when the going gets tough, ecologically speaking, Lecanorolichens either shapeshift for improved resilience or else fold their tents and away. And for another thing, it means that Lecanorolichens in particular but also lichens in general merit their sometime metaphors as biological chinking and crystallizations of place.

The point I’m leading to is this: that though the Lichen Rule gets stringently applied in the case of its namesake lichens, especially Lecanorolichens, yet in most other biological/ecosystemic systems its application is rather looser – meaning that the parts have more leeway to behave in their own self-interests without immediately bringing the system down around them.

Examples are legion, but two particularly pertinent ones will serve. First, look at how many human generations of technological devil-may-care it’s taken to bring the Climate Crisis about. Or again, look at how resilient western democracies have proven themselves to be against, what, three or four generations of humans who seldom give a moment’s thought to the consequences of their pursuit of personal rights in the absence of their corresponding personal responsibilities. Actually, and come to that, I suppose these are arguable two aspects of a single crisis.

All very impressive. Still, it has to be said that sooner or later, and it’s now looking to be sooner than later, the crows will finally come home to roost, as they must. For roosting crows are what you sooner or later get when you push hard enough, and long enough against right relation between the parts and the whole – that is to say, against the Lichen Rule.

Such is the meaning of the Lichen Rule in our time; and such is also, I think, the benefit of pondering from time to time a lichen held in the palm of your hand.