Adding my two-pen'urth. I think I read that on Cooks voyages to the south seas it was recored that the islanders used songs to row to. They went into the melting pot as well and we got such good 'uns as 'John Kanaka'. BTW in deference to my Polish origins I think I will use the spelling Zanties ...
I am in full agreement with the African bit as well. Not just black African either. I think the North African / Arabic influence must be taken into account as the Moors and other races of the area were also great sea-farers.