Jerry Coyne saves me some work by relaying the origins of this properly strap-referencing phrase. I was glad he stressed it because I've even encountered the error among more than one self-publishing author.

Mr Coyne says he thinks "free reign" is especially unacceptable as language evolution because it doesn't conjure its own meaning – but doesn't the temptingly coherent concept of "the ability to rule freely" seem like the factor fuelling the persisting misuse? In this case it does seem like evolution is true, and I imagine that's why.

• Jerry Coyne's elaboration