Researchers at the University of California San Diego for the first time have revealed why the shape of the feather shaft changes from round to square when it’s put under stress in a paper published in recent issue of Advanced Science. Nature almost always favors roundness. Only under special circumstances does it opt for square shapes. Examples include the cells of plants—which derive their name from the square cells of monks. At a larger, structural level, there are a few rare examples: the seahorse tail, a vine found in the Amazon that has a square cross section, and the feather rachis.