I have tried Googling where the upward inflection comes from but all I get are "Valley Girl" results.
My curiosity in this started with my new German Language course I'm taking and noticed that the inflections are present there as well for questions. If I remember correctly, when I took Italian and Spanish, the inflections were there as well. I thought it was odd that it was such a seemingly universal thing among Languages.
Why is this used? Are there known origins?
Though it may not be universal, I think in general that the rising inflection at the end of a question is actually epi-phenomenal. It is merely a confirmation of the body language of the speaker. Watch people who ask a question. When they phrase the question, they finish with a rise of the head, either directly or to the side. It is a clear invitation to come forward, to contribute, to continue the dialogue. Conversely, when a statement is made that is intended to be definitive, the head generally drops, as in a challenge. There is no invitation to continue. I think it is useful to remember that language is only the latest and most complex vocal/verbal means of expression of feelings and intents that have been expressed through other physical modalities for millions of years. Language is by no means primary, but has evolved as a means of confirming the other signals being given. Consider the difference between "You're leaving?" as a question, and the command "You're leaving!" Note how your head moves in each instance....
It is not universal. Alemannic (Swiss German) goes like
Hesch da schomol gse?
______------________
or
Wäge wa isch da jetz?
____-------__________
Rise towards the end of the question, and strict decrease for the last item/word.
So I guess it is arbitrary in the human languages.
Rising intonation with in questions is so widespread that there is no historical evidence regarding pre-modern English. The best that we can do regarding explaining the observation is (1) to say more precisely what seems to be true about human language and (2) to conjecture about functional explanations. It seems to be true that polar questions are more associated with a conventionalized intonation pattern with distinctive pitch rise towards the end, than with distinctive pitch fall (although more accurately, there is most often a longer rise and a short final fall). When declarative and interrogative sentences are distinguished intonationally, languages most often do so with rising intonation for questions and some other pattern for declaratives.
Why then would it not be the case that declaratives generally have rising intonation and interrogatives have falling intonation. I should also point out that rising and falling intonations are not exactly symmetrical, in that rising intonation typically reaches a higher pitch that falling intonation starts from. As is the case with many "why" questions in linguistics, the answer requires seeking functional the functional underpinnings that can lead to language evolution. There is a social (pragmatic) difference between questions and declarations, that a question is a request made of another person, a request for information. A request is generally understood to be subject to the willingness of the requestee, though of course you can demand an answer, that is not a typical question.
People tend to react positively to small things, such as children, puppies and kitties. Small things generally have higher pitch in whatever acoustic outputs they produce (for direct physical reasons). A higher pitch is therefore more likely to engender a positive response than a negative response (tendencies, not an absolute law of human behavior). Higher pitch in questions is therefore more likely to generative a positive reaction and compliance with the request than low pitch is.
I think there are instances where we can use an upward inflection at the middle of a questioning sentence for specific emphasis, as in “You’re going to WALK there?” It seems to mean that the destination and the going are not in question, but the mode of going is being questioned strongly. You can also lift the last word in that example, but it seems to give the utterance a slightly different meaning.
