Scratch my back and I’ll scratch yours

A familiar metaphor that expresses the mutual benefits derived from doing reciprocal favours for people. It is first cited from the early 1700s but it not known who coined it. Some sources maintain that it derives from naval floggings when sailors made pacts amongst themselves to go easy on one another when ordered to administer floggings. Other sources say it derives from observing the habits of monkeys. Both are unproven.