To continue with the last note...

I don't think that it's so much a matter of the Afro-American influence being understated, more than the influences of all the nations together being understated. I have friends majoring in music theory (Look for them either teaching or on a corner begging soon) who love to pick apart traditional shanties for the sheer joy of trying to figure out where they came from. Their general consensus seems to be that the three major influences of the shanties were the Irish emigrant wave (post-coffin ships), the African and Afro-American (as more left whatever they were doing ashore and joined aboard ships) and the European base (Drastically oversimplified... every one of the ocean-going nations contributed something to the mix)

It's problematic to try and lay claim for any one particular influence as being the one that shaped shanties for all time. If you read Dana's 'Two Years Before the Mast', he several times refers to the songs that were sung aboard his ships, and also those of the other crews (including a Kanaka crew singing entirely in their own language).

Perhaps shanties should be considered one of the true 'international' forms of singing?

M