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1795 a fellow by the name of Mungo Park was spending some time in Africa. I don’t know what the name Mungo might suggest to you, but it didn’t suggest to me that he was Scottish, but he was.
He subsequently wrote a book called Travels in the Interior of Africa in which he explains that Mumbo Jumbo “is a strange bugbear, common to all Mandingo towns, and much employed by the Pagan natives in keeping their women in subjection.”
Evidently a ranking male was decked out in some disguise and brought in to ritualistically intimidate any woman who had become quarrelsome. This evidently included public beatings while naked and tied to a post.
This 
account is related in Brewers Dictionary of Phrase and Fable and it’s consistent with The Oxford English Dictionary’s citation of mumbo-jumbo’s first appearance in English about 60 years earlier in 1738.
The words themselves are thought to possibly have meant “a revered ancestor”—that’s mumbo—“wearing a pompom”—that’s jumbo; this in reference to the disguise worn by the enforcer.
The most recent OED etymology says the mask itself might have been called maamajomboo.
Our current understanding of mumbo-jumbo is more along the lines of the OED definition number two: “Obscure or meaningless language or ritual; jargon intended to impress or mystify; nonsense.”
Such a meaning was understood in English at the time of those revelations of African wife abuse but it’s unclear—to me at least—whether the meaning derives from the fact that the person representing the mumbo-jumbo was only disguised and not really an important ancestor, or that these guys were babbling meaninglessly as they beat their women.
Most sources seem to point to the former.
Five days a week Charles Hodgson produces Podictionary – the podcast for word lovers, Thursday episodes here at OUPblog. He’s also the author of several books including his latest History of Wine Words – An Intoxicating Dictionary of Etymology from the Vineyard, Glass, and Bottle.
St Mungo is the patron saint of Glasgow, Scotland.
“Mambo Jambo” is the mask. Citing OED citing a source from 1738 might leave the impression that this cruel custom is a thing of the past. It is thriving today. If Mungo Park went back to Africa today he would find the terror as it was in 1738. The living horror is proudly posted on the internet! — “Oral sources recount that during a circumcision ceremony in “Mansaba”, one of the performing “Kankurangs” [mask-wearers] went into a compound to take a short break. There he took off his facial mask and coincidentally came face to face with a woman who was peeping. The woman expressed surprise as it was her own brother. Angered by his sister’s curiosity and revelation of his identity, he beat her furiously until she sustained injuries from which she later died. News of the homicide reached the authorities in Humus. Upon receiving the report, Da Costa, a ruthless [N.B. jpm] Portuguese Colonial commandant at the time, ordered the community to arraign the person who wore the mask to face murder trial, failing which the elders will face grave consequences. The entire community was thrown into panic and an emergency meeting was held to prepare a defence for their culture… The Cultural tradition is labelled on the internet as a “…heritage of humanity under the UNESCO Convention for the safeguarding of the intangible Cultural Heritage, the first workshop on the “Kankurang” traditions in The Gambia was organised by the National Centre for Arts and Culture (NCAC), held at Janjangbureh. The specific objectives of the workshop was to document the significance of the “Kankurang” to the communities which still continue to maintain the traditions, to find ways and means of preserving and securing the transmission of the traditions to future generations, to lay the foundations for the establishment of “Kankurang” centres, which will serve as focal points for research, information, dissemination and preservation of the “Kankurang” traditions. The Gambia and Senegal have also developed a project action plan, which involves the organisation of series of workshops with stakeholders in the respective countries with the ultimate aim of safeguarding the tradition for posterity and of which Guinea Bissau will also be brought on board in the near future.”
— The National Council for Arts and Culture (NCAC)operates under the auspices of UNESCO.
http://www.foroyaa.gm/modules/news/article.php?storyid=1664ies
[…] Wednesday’s word origin was for claptrap Thursday’s etymology, posted at OUPblog was for mumbo jumbo and Friday’s word root was for the word […]
Addendum. The cited author uses “intangible” to mean ‘untouchable, not to be meddled with’. Hands of our culture of torture!– Feminists, stamp out sexist pronouns!
“ritualistically intimidate any woman who had become quarrelsome”… Don’t you mean genital mutilation?
[…] mumbo jumbo originated with religious ceremonies in West Africa. In the Mandinka language, the word Maamajomboo described a masked dancer who participated in ceremonies. Former Royal African Company clerk […]
[…] jumbo originated with non secular ceremonies in West Africa. In the Mandinka language, the phrase Maamajomboo described a masked dancer who participated in ceremonies. Former Royal African Company clerk […]