Thinking about it, this is a trick question: there is no such thing as free trade.
I think THM may already have said this, likely several times. But take for example the fiasco with Bombardier and Boeing. There are government subsidies flying around, politicians exerting influence to get jobs in their corner of the world, whatever tariffs we have on aircraft, and who knows what.
So when TM says that Free Trade is “the greatest agent of blah blah blah” she’s spouting sanctimonious nonsense.
There is no free trade, there never has been and never will be.
So that means that back to the original question, the answer likely is actually the bicycle. Unless insects have bicycles of course. Or perhaps fire. Or something.