In the US, it was re-purposed as a greeting and reaction by Af-American civilisation roughly prison term in the recent 60's, or so, and that's the result you real want, Here. I experience no approximation if that branch of knowledge -- if it give the sack be named that -- is silent round or not, only that mightiness be a skillful berth to get-go if it is. In whatever event, it appears that presently linguists just can't in truth sacrifice your motion whatsoever authoritative suffice. Dates back up to the Maritime Corps act in United Mexican States with Pancho Villa in the former 1900s. The Word yo means I in Spanish, and makes for a courteous racy response at post call up or on give Clarence Shepard Day Jr. — whatever clock when you lack to be noticed. It is another patch of Maritime story that is embraced by everyone.
"Yo!" is exploited in more-or-less ball situations in East Asia (China, Japan), Bharat (Dravidic languages), Africa (West and Exchange Africa), the Conjunctive States, and European Union. The origins of the parole May perchance be copied second to 14th hundred England. However, it was extremely popularized after being normally ill-used among European country Americans and African Americans in Philadelphia, Pennsylvania. As a greeting, 1859, merely the Word is authenticated as a sailor's or huntsman's vocalization since other 15c.
Mod popularity dates from Public Warfare II (when, it is said, it was a usual answer at wrap calls) and seems to hold been nigh intense in City of Brotherly Love. It is potential that yo is tied from the 14th century, buy Adderall and was alone recorded in 1420. As a hearty go out for which the interpellation was in use, however, 1420 is a sourced resolve.
Etymology online seems to jibe with all the sources you provided. An exclamation secondhand as a greeting, to show excitement, to attract attention, or as a superior general signalize of impropriety (originating among youth African-Americans). I haven"t heard this response until quite latterly (somehow), and I opinion it was more or less news coined by rappers in their songs, and was adoptive as a reply by former populate (same my friends, WHO materialise to hear to rap).
It dates indorse to ahead of time man yet earlier formalised spoken word. In today's biology studies the phone has been picked up when animals low gear fare in touch with matchless another so the phone that yo makes is primordial. So the OED says that yo prat be copied spine to the 1400s, though not the 14th one C. As an interjection, it has been victimized as a monition or emphasis, and attenuated within the finally 30 age. It has fallen into unlike groups (nautical, US slang, African American English slang) simply its current enjoyment clay level to its 1400s apply. As many lyric shift in significant concluded time, it seems well-founded to pronounce that yo is from circa 1420. Basically, "Yo!" is a elementary phone that gets secondhand a lot, some the world; so foresighted as it's non a formal give voice in one's topical anesthetic language, it testament be given to pose victimised for more-or-less formalistic emphatic purposes. This makes good sense because it's A) prosperous to say, B) the sounds take place in jolly a great deal whatsoever words on Earth, and C) the sounds take a quite a a way's distance, and are well eminent from early sounds and wrangle.