Etymology of reduplicative compound "nitty-gritty"

I've always been curious about that one and I've come across many contending theories for the etymology of nitty-gritty. English is quite fond of these reduplicative compounds.

I'd like to know whether some consensus has been achieved in this area.

Alain, as you have done me so much service with your etymologies, I simply must do you one ;)

Nitty-gritty comes by way of African-American culture, southern and south-western African-American culture to be exact, and the word was attested orally as early as the 1920s. Let me quote from a paper, The Real Nitty Gritty by a W. R. Higginbotham and J.A., from whence nearly all my information comes:

The earliest uses of nitty-gritty are in registers characteristic of black America, and they continue: jazz music and musicians (1961, 1963a, 1965, 1966a, 1969c, 1971c), civil rights and black power (1963b, c, 1966d,1967c, d, 1968a, b, 1970d), and as an ingredient in that elusive quality that pervades and identifies all things black-soul (1966a, b, 1967b, 1969b, d).

_{The citations are left in without a bibliography, so that you may see the date of first attestation.}

From African-American culture, it then apparently passed into the lingo of college students at about the time of the 1960s, by way of popular music, and was probably helped in its adoption by the general countercultural mood of that era. (Remember this was the era of "the [Civil Rights] struggle"; knowing the obscure argot of an oppressed people would have likely seemed appealingly dangerous and sexy to college students.) From there, it spread into the general culture via writers and high-circulation periodicals, such as The New York Times and Newsweek. One song written in 1963, by a Licoln Chase, titled simply The Nitty Gritty, appears to have been especially influential in the uptake of the word. I reproduce the first few lines:

Some folks know about it, some don't.
Some will learn to shout it, some won't.
But soon or later, baby, here's a ditty,
Say you're gonna have to get right down to the real NITTY GRITTY.
Let's get right down to the real NITTY GRITTY,
now one, two NITTY GRITTY,
now yeah, boom NITTY GRITTY,
now ooooh-iee. Right down to the real NITTY GRITTY!
Oooh-oooh! Oooh-oooh!

More from the paper:

The word seems to have been first used as a noun (1961-63); and, although it passed easily and early in its recorded history into adjectival use (1964b, 1966d, 1967c, d, 1968a, 1969e, f, 1971a, 1973c), it has remained predominantly a noun. Indeed, by far the most frequent collocation of the term is some form of the expression get right down to the real nitty-gritty, which, in one variant or another, accounts for about half of the total number of citations. That phrase also accounts for the earliest uses.

But you're probably wondering how this phrasing get down to the nitty gritty was coined originally. Well, here's where it gets disgusting. In fairness, there is actually some disagreement about the following explanation in the paper -- Higginbotham promotes the idea in the beginning, while J.A. argues against it -- but it is easily the most intriguing one I found therein, so I must reproduce it. Apparently, the "nitty" in nitty gritty refers to actual nits, as in lice, and the gritty was initially a reference to ground hominy, and then became a reference the grinding action one uses to reproduce the staple. Of course, that in turn was easily sexualized in meaning so that gritty also came to describe the grinding action of raw, bestial intercourse. Thus, getting down to the nitty-gritty means getting down so deep in a woman that one feels everything of her movements, and I do mean everything. The paper gives this joke to illustrate:

Both black men at Amarillo insisted to me that nitty gritty sprang from what they described as an old, black, nearly pointless joke that goes:

A man having intercourse with a smart-alecky girl took an unusually long stroke, making her jump. Thinking he had impressed her, he asked, "Did I hit it, honey?" "Yeah," she said. "Wrong way. You hit the real nitty gritty."

Wow! Amazing language, our English.