@hyp
Feedback mechanisms, think recursion, are surprisingly new even as they are ubiquitous in biology and many systems today. This may be why we have trouble
naturally grokking recursive systems like our own minds. (Many zen koans are attempting to get one to see recursion that seems counterintuitive)
1800s saw many new ones.
One of the first?
The floatball mechanism we still have in most home toilets.