Edited by Azizi Powell
This pancocojams post provides examples of the word "yo" from two West African languages: Temne and Twi.
Update: 4/3/2017- I've added a children's song in Ewe and Akan [Twi] which includes the word "yo".
The content of this post is presented for etymological, folkloric, and cultural purposes.
All copyrights remain with their owners.
Thanks to all those who are quoted in this post.
PANCOCOJAMS EDITOR'S NOTE
While internet surfing for the etymology of African American slang, I happened upon a discussion on a linguistic website in which bloggers were trying to find out the origins of the word "yo" as popularized in the United States by Hip Hop culture and by other populations:
Kyle Pearson, http://english.stackexchange.com/questions/40408/whats-the-origin-of-yo, edited Sep 3 '11 at 10:54
answered Sep 2 '11 at 17:57
"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.”
I added italics to highlight those words.
After reading that comment, I searched for online examples of the word "yo" or similarly spelled words in West African and Central African languages-used as an interjection or otherwise.
Here are some points that I want to make prior to presenting the small number of examples of "yo" that I've found in two traditional West African languages:
I disagree with that commenter Kyle Pearson that the interjection "Yo" is used during "more or less formal situations in the United States". However, that may not have been what Pearson meant to convey in that sentence.
Unfortunately, Kyle Pearson didn't give any information about which West African and Central African languages contain the word "yo" and it's very difficult to find any such information and examples online. Consequently, I want to share these examples that I did find online and in one book (R. S. Rattray's 1922 book entitled Ashanti) and in an online page about learning the Twi language.
I'm not a linguist. But, for what it's worth, as an African American self-described "community folklorist", it seems to me that for some time [since the late 20th century?] the interjection "Yo" has been largely retired among African Americans except when it is consciously used to evoke the spirit and times of the late 1960s to the late 20th century Hip Hop culture.
Documenting examples of "yo" words in African languages doesn't mean that I think that those languages or any other traditional African languages directly or indirectly influenced the 1960s to late 20th century Hip Hop culture's use of the word "yo" in the United States. I know too little about this subject to state or imply that position. However, I also don't automatically discount the possibility of that influence.
I hope that people who know traditional African languages will add information here and/or elsewhere online about the word "yo" in those languages.
EXCERPTS ABOUT THE WORD "YO" AND "IYO" IN TEMNE
Except for information about the Temne language, these excerpts are given in no particular order. They are numbered for referencing purposes only.
Temne… is a language of the Mel branch of Niger–Congo, spoken in Sierra Leone by about 2 million first speakers. One of the country's most widely spoken languages, it is spoken by 30% of the country’s population. It also serves as a lingua franca for an additional 1,500,000 people living in areas near the Temne people. It is closely related to the neighboring Kissi language."
JOSEPH E. HOLLOWAY Ph.D, 
"Yah (yo) Crebo ya, used after commands; Temne yo, used after statements or commands. An emphatic concluding particle: “Indeed!” Often said in endearing tone, thus softening a statement or command. Also black West African and Caribbean English ya, said after statements or command."
From https://books.google.com/books?id=iLo0AQAAMAAJ&pg=PA19&lpg=PA19&dq=temne+iyo+meaning&source=bl&ots=9DplTy5BZA&sig=5uI8h6O3SxbqaHktpA-s6QLWfBM&hl=en&sa=X&ved=0ahUKEwjk0YrBgIHTAhXmz4MKHVG_BlcQ6AEIMDAD#v=onepage&q=temne%20iyo%20meaning&f=false A Handbook of the Temne Language - Page 19 - Google Books Result
Rev. A. T. Sumner - 1922 - Temne language
"Grammar 33. Easy conversation
L- Tei ti yi h
S. Re man- ko-e? (1)
L- I ko ro pet.
S- Ko man ko yo-e?
L – I ko kori (2) o-kas ka mi.
S- o- kas ka mu o yi ri ro pet?
L-I, o yi ri ro pet.
S- o kara (or ya) ka mu o yi ri ro-i?
L-I, I, o, yibe, ri, o, , ko, ro, Kamp, kere, o, ti (will), der, ninan
S-I, kora o-kas ka mu yo ? (3)
S- Mam pia, yo
S-Iyo, mam pia, yo*.
Notes 1. Where are you going? Man is the imperfect tense form of the second personal pronoun, singular number. The e after ko is an expletive. 2. Kori- to visit …Yo is an idiomatic expression whose meaning is conveyed by the sentence in which it is used. . 3. Yo is an idiomatic expression whose meaning is conveyed by the sentence in which it is used.
kori o-kas ka mu, yo ? may be translated “Give my compliments to your father, will you?
mam pia – good- bye - All right, good-bye.”
These words are given without the accent marks or other symbols over certain vowels.
"Iyo seke- hi
Iyo, senenkane so- O/k, we shall see again"
From https://books.google.com/books?id=LXMuB31O628C&dq=Temne+yo&source=gbs_navlinks_s A Collection of Temne Traditions, Fables and Proverbs: With an English Translation; Also Some Specimens of the Author's Own Temne Compositions and Translations, Christian Friedrich Schlenker, Church Missionary Society, 1861 - Folklore, Temne - 298 pages
[Google books, page 296 Temne [one entry from that page]
"Yo ,adv, thus, so, in this way, in the same way”, or manner, the same kind
e.g. yo a pa* - thus he said;
yo o yo** - thus he did
This form is used before words with the vowels o and u."
*with accent mark over the a
**accent mark over the o
EXCERPTS ABOUT THE WORD "YO" IN TWI
From http://www.amesall.rutgers.edu/languages/128-akan-twi Akan (Twi) at Rutgers
"Akan refers to the language of the Akan ethnic group of Ghana. It is also spoken in the central and eastern part of Cote d’Ivoire. Akan comprises three main mutually intelligible dialects: Fante, Asante Twi and Akwapim Twi. Asante Twi is the widely used. Akan is the most widely spoken and used indigenous language in Ghana. About 44%, of Ghana’s population of about 22 million, speak Akan as first language. However, about 80% of Ghanaians speak Akan as a first and second language. It is officially recognized for literacy, at least at the lower primary (Primary 1-3) level, and studied at university as a bachelor or masters program. It is the most important indigenous language of Ghana. It is the language of the Western, Central, Ashanti, Eastern, Brong Ahafo regions, and the northern portion of the Volta region of Ghana."...
Excerpt #2 [with notes and related quotes]
Ashanti by R. S. Rattray
[This book was first published in 1923; Oxford, Clarendon Press, reprinted University Press Oxford, 1969
“The chief, Yao Kramo*, standing on a small raised platform, on the left of the altar, now removed his cloth from his shoulder and fluently and in a loud voice spoke as follows, while the old high-priest and two men who held a sheep stood beside him. His speech was punctuated by the loud Yo! Yo! of the Tano linguist.
Aban mu Ta Kese, afe ano ahyoa, ena me ne manfo yi ye fua ye nsam oguan yi de re ma wo, wo agyina yen akyiri akyigyina pa. Wa fre ahaha ne nono ama obawofo awo. Abofo de ‘tup ko wuran a, w akum nam.”…
Ta kese of Aban (1), the cycle of the year has come round, therefore I and these my people hold this sheep which is from our hands and give it to you. May you stand behind us with a good standing. May you call upon all the spirits of plants and beast that the bearers of children may be fruitful, and that the hunter who takes his gun to go to the forest may kill meat”...
(1) That part of the town of Tekiman where the temple of [the god: abosom] Ta Kese stands is so called."
If I correctly understand this term, "linguists" are spokespersons for high priests.
Read the Addendum below for notes about this quote.
Adesuadeɛ a ɛdi kan: 1st Lesson, Twi Kasa Nnyegyeɛ (Twi Language Sounds) Nsɛmfua Afoforɔ (New Words)
"English phrase: Repeat what you said.
Twi phrase: ka bio.
Pronunciation : kah BEE-YO
literal translation - Say again.
English phrase: Goodbye
Twi phrase: yɛbɛhyia bio
Pronunciation -ye-BAY-shee-YAH BEE-YO
literal translation: We will meet again"
"Akan...is a Central Tano language that is the principal native language of the Akan people of Ghana, spoken over much of the southern half of that country, by about 58% of the population, and among 30% of the population of Ivory Coast.
Three dialects have been developed as literary standards with distinct orthographies: Asante, Akuapem (together called Twi), and Fante, which, despite being mutually intelligible, were inaccessible in written form to speakers of the other standards.
Important words and phrases
Yoo - [pronounced] oh; [meaning] Okay/Alright"
ADDED ON 4/4/2017 an Ewe and Akan song
From https://books.google.com/books?id=HUK_AAAAQBAJ&pg=PA109&lpg=PA109&dq=akan+word+yoo&source=bl&ots=_7TwY2nIH_&sig=sn0-tj8JJgpRVUlgcaMhyGKlFKc&hl=en&sa=X&ved=0ahUKEwjAhYLVu_7SAhUX22MKHd7bDJ8Q6AEITTAJ#v=onepage&q=akan%20word%20yoo&f=false Kaleidoscope of Cultures: A Celebration of Multicultural Research and Practice
edited by Marvelene C. Moore, Philip Ewell
Lesson Plan "Yo Yo Yo" (Yes, yes, Yes)
Introduction The philosophy behind this game and song is to teach children the need to be law-abiding, respectful, and responsible in their behavior. During the game the leader assumes the role of the parent, a teacher, or an elder in the community. In a social situation all children are supposed to abide by rules. If someone is not bold enough to own up for any wrong that was done, then it is up to the other children to point out that child for his or her wrongdoing. In the game the leader says "Yo" ("Yes") at which time everyone has to be quiet."
This "procedure" section continues, indicating that other children reprimand the child who has done wrong by being "rebuked" spanked", or hit by other members" while singing this song. [Clearly, this play instruction doesn't "translate" well in the United States and other Western nations.]
Yo Yo Yo (Ewe)
Wana ya wa yo (Akan)
Esi na wa yo! (Akan)
Yoo, yoo, yoo
Wahnah yah wah yoo
Ehseh nah wah yoo
Tah bor bor
Yes, yes, yes!
Who says yes?
Esi says yes.
So get (bend) down
"Esi" is a girl's name.
Here's information about the Ewe language from http://www.omniglot.com/writing/ewe.htm
Ewe is member of the Volta-Niger branch of Niger-Congo languages with about 3 million in the Volta Region of south-east Ghana, and also in southwest Togo and in parts of Benin. It is recognised as a national language in Ghana, where English is the official language, and in Togo, where French is the official language."...
Is "yo" an Ewe word for "yes"? http://wikitravel.org/en/Ewe_phrasebook indicates that "Eeh" is the Ewe word for "yes".
Here is some information that helps clarify the reference to "the Tano linguist" in the quote given as Excerpt #2 in the section about the Twi language:
"English: In Ghana, especially in the Ashanti land, gives it several of Tano shrines or little temples for the worship of the Akan God Tano. Tano is the name of a river and also whose river deity in the western part of the Ashanti core region. In the Akan religion is Tano a deity of protection and also the God of War. Tano as protection deity is also the godly antagonist of the death, with whom he is in continous race duel. In the case that Tano approaches a dying person as first than this human belongs him and the death has no right on this one. Tano is the twin brother of "Bea", another river deity in Asante. "Tano" and "Bea" are both "Abosom", means "children of Nyame" and as such they stand in the godly hierarchy of the Akan deities below of the creator god Nyame."
From http://countrystudies.us/ghana/52.htm Ghana Traditional Religion
"The supreme being is usually thought of as remote from daily religious life and is, therefore, not directly worshipped. There are also the lesser gods that take "residency" in streams, rivers, trees, and mountains. These gods are generally perceived as intermediaries between the supreme being and society. Ancestors and numerous other spirits are also recognized as part of the cosmological order."
p. 216 Rattray's book Ashanti
"It is not, however the Sky and the Earth deities who in Ashanti are held to the prime factors in shaping and influencing the actions and destinies of mankind. These great unseen powers are generally too remote or perhaps too mighty to be concerned very intimately with the individual clan, much less with the individual member of that clan, and the predominant influences in the Ashanti religion are neither ‘Saturday Sky god’ nor ‘Thursday Earth goddess’, nor even the hundreds of god (abosom), with which it is true the land is filled, but are the samanfo, the spirits of the departed forbears of the clan.
Sky god -Onyame (‘Nyame)
Earth goddess – Asase Ta, Aberewa (Ya, Old Mother Earth)
Here's some quotes from Rattray's book about the role of the "linguist":
"I was later informed that just as upon earth it is not etiquette for a king to speak direct to anyone except through his official mouthpiece or spokesman, the okyeame (usually but quite wrongly rendered ‘linguist’ throughout the Gold Coast)m so with the gods, each had his okyeame."
"The ‘linguist of the chief (who, it must be remembered, was also high-priest) was now called upon the representative of the Tekiman priest, who had accompanied me, to state the object of my visit”.
A "linguist" appears to be different than a "herald". Here's a quote from that 1922 book which mentions a herald:
"During this speech the herald was continually breaking in with, Tie! Tie!! Kom! fwe! fwe! (listen, listen! Silence! behold! behold!"
For folkloric reasons, I'm also including this quote from R. S. Rattray's Ashanti book references a portion of the chief's speech that is given above
p. 209 [note 1]
"This idea of protection from something attacking one from behind – the invisible- is seen throughout all the ceremonies. Almost every prayer ends with “stand behind me with a good standing”.
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