Whoever posted this at 0415 pm -- Do you really imagine I would have posted such a question without doing a web search first

Sorry, that was me. I got the quotes from Douglas Adams (both versions) as the first, second, third and fourth returns from Google. But Google knows I am in the UK.

I am fairly sure Adam's did coin the phrase, as he did many others amongst people who followed what was, at the time, a cult radio program.

Any how the explanation, which Ebbie and probably Rapparee, know, is THIS Adam's may have been making an oblique reference to an early scene in 2001- a Space Odessy.

To us in the UK it makes some of you look primitive (and dangerous) in your attitude to guns and others of you look primitive in your inability to change things. Except the term that follows from the Adam's quote is not 'primitive' but 'un-intelligent', which is unfair on the caveman.

I have been to the USA, I have stopped the car in a prosperous neighbourhood to read the map, had a guy coming back to his home pull up in front, take something heavy from the glove compartment (or whatever you call it) and put it in his pocket, come over with his hand in that pocket, find that I was a white guy with an English accent, give me directions, then go back and return the heavy object from where he got it.

I don't think the heavy object was a rock.