etymological question: "jack shit"

[Douglas G. Wilson]

>>Q: "What did you do all day?"
>>
>>A: "Jack." = "I didn't do jack." = "I did jack." = "Jack shit." = "I didn't
>>do shit." = ...
>
>these all occur, but not in general interchangeably.  You're not
>saying they're all synonyms, are you?

Not in general, but nearly so in the exact context of this Q-and-A.

My point is that there is a tendency to fill in the blank with an almost
random obscenity or rude word. Logically preferable alternatives such as "I
didn't do a single erg/joule/watt-hour of useful work" just don't occur
(physicists and others, correct if necessary!).

In the expression "not worth ...", one will hear "not worth a cent", etc.
-- but how often, compared with "not worth shit"?

>"diddly-squat" as a minimizer (or more properly "doodly-squat") is
>actually attested earlier than "squat", for what it's worth.

Oops, I even knew that once. Another neuron which has failed (too much
applejack perhaps). In its place we can put 20 other examples, however.

My point is rather general and tentative: there are "didn't do/know shit"
(rude/obscene), "didn't do/know dick" (rude/obscene), "didn't do/know
f*ck-all" (rude/obscene), etc. ... If I hear "didn't do/know jack" in a
similar context and register, I can't help thinking that it may have a
rude/obscene origin also -- assuming that there are reasonable candidates!

The 'small coin' hypothesis would remain another tentative possibility, and
doubtless there are many others.

A parallel is the derivation of "don't give a damn" from the dam,
apparently a small coin used in India. I heard this when I was a child.
Later I learned from what I thought was an authoritative source that this
story is bogus, and that the original word was plain old "damn". Somehow
this latter rings truer to me. What do the experts think today?

I guess "not worth a rap" truly comes from the word for a coin?

-- Doug Wilson