Not a historian, but you'd likely have a better chance of getting a comprehensive response on /r/linguistics

You may be interested in this r/linguistics thread from 2013 and in particular the response from u/purple_forbidden.

I would like to add, that this not only happened to english speaking countries, in Poland it's just as common. Is there any reason to the spread of such usage and if so where did it originate?

Hijack: in pop culture we see these types of vocalizations used essentially all throughout history. I'm thinking of cavemen grunting uh-uh to say no... pretty common thing in fiction. So is there any evidence that these vocalizations are not just an English thing but a common feature of many languages, and if so, would that give us any further idea on when they first emerged?

This question might be hard to answer without a great deal of conjecture. The OED's first entries for "uh-huh" and "uh-uh" are both from Dialect Notes 5 of 1924. The OED doesn't necessarily have the earliest attested instance, but at least that establishes both at nearly 100 years old. Interestingly Dialect Notes represents the affirmative as uh-húh, which seems to be an indication of the rising contour.

Of course, one of the difficulties here is that it's hard to reconstruct pitch contours from written language. For that one place we might turn is musical sources. There's a phenomenon that's been called the "stylized interjection" that (contemporary) English speakers use in a number of playful/expressive contexts, like chanting "airball!" or calling "dinner!" This tends to fall by about a minor third (300 cent or 1/4 of an octave), though there's a fair amount of variability in realization. (See Jeremy Day-O'Connell, "Speech, Song, and the Minor Third: An Acoustic Study of the Stylized Interjection," Music Perception 30/5 (December 2012): 441-462.) That study is of contemporary English speaker, so it's of limited historical use. What I find suggestive is that you see similar sorts of gestures in European music from the 18th century. Italian (and Italian-influenced) opera of the time used a practice of semi-spoken dramatic recitation called "recitative" that was notated with standard musical notation. One finds, written specifically as falling minor thirds, expressive gestures like vocatives, valedictions, and plaintive sighs ("oh dear!" and "ah, no!"). These might share a bit of the semantic range of "uh-uh." (It might, however, be more similar to "uh-oh" than "uh-uh.")

I bring it up because there's another well-documented recitative gesture that serves as a kind of musical question mark, showing up at the ends of questions in recitative. It's contour is middle-low-high, just like the "mmm" for "I don't know." The contour for "mmm" mirrors the contour of "I don't know," which is constrained by the usual principles of intonation contours in English. But, again, it's suggestive that it's the contour one finds in recitative.

Those are pretty tenuous connections--I only bring them up because it doesn't seem like we're likely to be able to do better with historical documents. (Recorded sound might be useful, but it'll only take us back about as far as the OED's citations, at least with any hope of capturing such informal speech.) If the connection is meaningful at all, what it suggests is that these vocal gestures are shaped by constraints that transcend individual languages (e.g. something relatively cognitively hardwired, as might be the case for the "stylized interjection," or the constraints of a semiotic system based purely on contour--a two tone gesture can only go up or down, and a three tone gesture has only so many non-monotonic options.)

I would note that historians work with written sources. Hmm, and the like rarely appear in non literary written sources. For example, I use criminal cases and bureaucratic documents. In the 16th c. when recording witness testimony filler words were omitted and no one writing a formal report or letter would use a filler. I have no doubt they were used, but they are unlikely to be recorded for posterity.

So far there's been 2 jokers posting "mmm", apparently to indicate they don't know. Such posts are spam, and we have a very low tolerance for spam and spammers.

When attempting to answer this question, please keep in mind our requirements for answers.