Note to GUEST,AKgrown: The 'f' word is certainly older than middle English. There are close analogues of it in most of the Germanic tongues and some of the Slavic ones.

And for the 'finger', in The White Goddess, Graves says that in classical times, the middle finger was associated with the god Saturn and popularly called 'the fool's finger' because there are more fools in the world than anything else (see the section on 'dactyls'). The classic equivalent of the modern 'finger' was called the 'fig' and was formed by thrusting the tip of the thumb between the two adjacent fingers. The first time I saw it mentioned in print was in a footnote in The Divine Comedy. The gesture is still used in southern Italy.

While I'm at it, the 'thumbs up' gesture, as used in the Roman arena, did not mean 'spare him'. It was made with an upward jab and meant 'gut him'.