But surely they would reproduce? There is no genetic evidence of African genetics in south americans.
Also, there are no African skeletons found. But i admit it can be difficult to find a skeleton in a jungle.
It seems to me that it is very difficult for a foreigner to just come ashore and become leader of a people that don't even understand what the dude is saying, especially when those Olmecs already had leaders which controlled a vast army.
"It is very difficult for a foreigner to just come ashore and become leader of a people that don't even understand what the dude is saying."
So this is why it was so hard for Cortez with a few hundred men to conquer a few million Aztecs? Furthermore as blam points out in his comment about 8 or 9 past this yours, this was a period of great upheaval worldwide. From my recollections (which I know I should refresh) it was only about this time that Olmec building and power really took off. Perhaps foreign knowledge of military and civic bureaucracy whether from China or the Middle East or both had an influence. Also, perhaps the "Phonecians" already had some trading contact, and linguistic knowledge there. With a worldwide upheaval (including severe weather) it would not have been hard for a fleet to be stranded and settle in, or to escape there from strife at home. Or even take the reins of power from native rulers who had failed to protect their people from the cosmos and lost "the mandate of heaven."
As to the genetic matter. If there was no steady influx of African settlers, they blood lines of African war chiefs would soon have been diluted to the point of near disappearance. Have you looked carefully at all the light skinned "Blacks" in this country after only one or two centuries, much less 3 millenia. Furthermore, I think that only a few thousand people have been tested and compared for the studies of worldwide migrations. Perhaps no one has tested coastal Mexicans, and African areas where mercenaries were normally recruited. There is so much exciting work still to be done in that whole DNA/Mitochondria area.