Team ‘Disproves’ Da Vinci’s Rule of Trees — Or Does It?

Wales’ Bangor University recently claimed that a group of its scholars had “disproved” Leonardo da Vinci’s “rule of trees.”

But the rule, which comes in multiple wordings from myriad corners of the internet, does not directly engage with the topic the researchers studied.

And the researchers themselves did not claim to have disproved the theory.

Contentious consensus

The theory, as best as ExplorersWeb can synthesize it from the many, sometimes conflicting sources available is this:

The thickness of a limb, before it branches into smaller ones, is the same as the combined thickness of the limbs sprouting from it.

That interpretation owes to ScienceNews.

Multiple articles and papers have sought to discredit da Vinci’s theory. General scientific acceptance favored it until recently, because, as one researcher put it, “people really haven’t tested it.”

But why did da Vinci come up with the rule of trees? Again, multiple opinions hold court, but the most prominent is that he used it to create better drawings.

A fallacy in the definition

The Bangor University team, which published its findings in the journal PNAS, concerned itself with vascular channels in tree tissue.

Vascular tissue in trees consists of xylem and phloem. However, tree tissue comprises other structures such as cambium, which “divides xylem and phloem, and results in secondary thickening.” There’s also tree bark, which is dead phloem.

The Bangor University group finds that “plant morphology is dictated by vascular optimality and not the assumption of constant sapwood area across all branching levels, contradicting Leonardo’s rule.”

But this claimed contradiction is propped up on a fallacy: the rule of trees doesn’t concern itself with what dictates tree morphology, but instead how it appears.

Data hazards

It’s an intellectual chasm that researchers have, evidently, neglected for five-plus centuries. That’s mostly because the theory appears to generally apply and, well, it’s pretty hard to test.

Most field data supports the rule of trees. But, as InsideScience points out, gathering it is tedious.

“The [experimental] data is very scattered,” said physicist Christophe Eloy, who previously vindicated the rule through computer modeling. “If you’re looking at big trees, there’s thousands of branches, and it takes a lot of undergrads to measure it.”

Applying the Bangor University team’s findings could help explain why trees tend to form the shapes that they do, on a vascular level. But will it show whether trees conform to da Vinci’s rule? No.

Sam Anderson

Sam Anderson takes any writing assignments he can talk his way into while intermittently traveling the American West and Mexico in search of margaritas — er, adventure. He parlayed a decade of roving trade work into a life of fair-weather rock climbing and truck dwelling before (to his parents’ evident relief) finding a way to put his BA in English to use. Sam loves animals, sleeping outdoors, campfire refreshments and a good story.