Evolution is cleverer than you are.
Orgel's rule from molecular biology. Its general form is a warning against declaring a feature useless: the absence of a known function is evidence about the observer, not about the system.
In practice
- A protein that looks like a design error turns out to be doing three things at once.
- A legacy process that appears redundant is holding together two systems nobody has mapped, which is Chesterton's fence in biological form.