Tbh those black South Americans were most likely from the slave trade which would be a much more recent event. If you notice North American Native Indians look quite similar to South American Native Indians, not African. so they would actually be the original ones over there.
http://www.roperld.com/graphics/MigrationMap.jpg
http://en.wikipedia.org/wiki/File:Spreading_homo_sapiens.svg
Couple of Maps to give an idea of the route the original people took to the Americas. Also the last ice age started roughly 100,000 years ago and ended 11,700 years ago, The coldest part, when massive glaciers extended as far south as Britain, happened between 25,000 and 20,000 years ago. So bare in mind all that ice the worlds oceans & seas would have been a fair bit lower, thus making the Bering strait a possible land bridge from Asia to North America.
Are you saying tribes in Brazil are descendants from slave ships, yes their are slave descendants in Brazil, their are all kinds of people there but pure native Brazilians don't look like native american Indians and they also don't look like most Africans, but they're more closely related to Africans even though they have their own look, search Brazilian tribe, then search american Indian, both tribes/people look very different, both originate from a different place and time.
what i'm saying is, Brazilians got their first, as all humans have come out of African, the Brazilians spent less time in other lands before america and have changed the least, their facial features are more closely linked to an Africans than say a american Indians, which are more closely linked to a Mongolian.
Dr Alice Roberts made a show explaining what happened which went into detail about humans out of Africa.. Look her up, she's easier to understand than random links on the internet.
Anthropological and genetic evidence indicates that most Native American peoples descended from migrant peoples from North Asia (Siberia) who entered America across the Bering Strait or along the western coast of North America in at least three separate waves. In Brazil, particularly, most native tribes who were living in the land by 1500 are thought to be descended from the first Siberian wave of migrants, who are believed to have crossed the Bering Land Bridge at the end of the last Ice Age, between 13,000 and 17,000 years before the present. A migrant wave would have taken some time after initial entry to reach present-day Brazil, probably entering the Amazon River basin from the Northwest. (The second and third migratory waves from Siberia, which are thought to have generated the Athabaskan and Eskimo peoples, apparently did not reach farther than the southern United States and Canada, respectively).[citation needed]
An analysis of Amerindian Y-chromosome DNA indicates specific clustering of much of the South American population. The micro-satellite diversity and distributions of the Y lineage specific to South America indicates that certain Amerindian populations have been isolated since the initial colonization of the region.[5]
this makes sense
