I have some friends, and they say “Yo!” when I call them. I haven”t heard this response until quite recently (somehow), and I thought it was some word coined by rappers in their songs, and was adopted as a response by other people (like my friends, who happen to listen to rap).
So I was rather surprised, when looking this up on Wiktionary, I read:
(military slang) Present! Here!
Sergeant: Smith?
Private Smith: Yo!
I thought to myself, “Obviously this ain’t coined by them rappers!”
Then, I saw a similar question on Yahoo Answers, with an answer stating (one link provided):
Yo is an American English slang interjection. The origins of the word may possibly be traced back to 14th century England. However, it was highly popularized after being commonly used among Italian Americans and African Americans in Philadelphia, Pennsylvania.
Clicking on the link provided, it turns out to lead to Answers.com. But the funny thing was, the new source included this information:
An exclamation used as a greeting, to express excitement, to attract attention, or as a general sign of familiarity (originating among young African-Americans). (1966–) .
I am inclined to think that the word yo came from the 14th century, but have no real evidence to say so. Can anyone provide solid stuff? That is, did it come from a military response, or a word used among young African-Americans in 1966?
Edit: I am asking specifically in relation to yo being used as a response/reply.
Best Answer
I think that any etymology of "Yo!" that goes back only a few hundred years is woefully incomplete and quite absurd.
"Yo!" is used in more-or-less formal situations in East Asia (China, Japan), India (Dravidian languages), Africa (West and Central Africa), the United States, and Europe. That usage range puts it well beyond the purview of Indo-European, and suggests that its origins could lie entirely outside any formal etymology - but if it does have an origin, it obviously ain't English (as your source up there says, suggesting it may have come from Africa, or the Mediterranean, or both).
Arguing that this simple sound is derived from "an exclamation" back in AD 1400 is saying nothing more than "Back then, in AD 1400, nobody knew where it came from, either." Compare, for instance, the exclamation "Zounds!", which has a certain date of origin, and a certain meaning from which it is derived: "Yo!" has none of that.
Basically, "Yo!" is a simple sound that gets used a lot, around the world; so long as it's not a formal word in one's local language, it will tend to get used for more-or-less formalized exclamatory purposes. This makes sense because it's A) easy to say, B) the sounds occur in pretty much any language on Earth, and C) the sounds carry a quite a way's distance, and are easily distinguished from other sounds and words.
In the US, it was re-purposed as a greeting and response by Af-American culture some time in the late 60's, or so, and that's the answer you really want, here. It may have been absorbed into Af-American culture through Basic Training in the US military, during Vietnam (or WWII, as suggested by the other poster, above), or it may be a holdover from something more ancient, perhaps an African dialect; it's to answer questions like this that the idea of "ebonics" was once promoted. I have no idea if that discipline -- if it can be called that -- is still around or not, but that might be a good place to start if it is. In any event, it appears that currently linguists just can't really give your question any definitive answer.