It’s also called Da Vinci’s Rule of the Trees; and knew about this rule 500 years ago and it was recently validated by scientists who used ‘a lot of grad students’ to measure it. The rule hadn’t really been tested until recently.
Now scientists are trying to figure out *why* this holds true. There are currently two leading explanations for why this is true: One is that it’s because this ratio is conducive to effectively transporting sap.
The second, and the one that a new paper has given a lot of credence to, is that it’s the optimal size for resisting wind damage. They built sophisticated computer models that simulated a full tree, and then measured how thick branches had to be to minimize wind damage, and the Da Vinci rule always seemed to be validated.