Researchers studies short stretches of mitochondrial DNA (mtDNA) from museum tooth samples of ancient Botocudo individuals, extracting a piece of the tooth cores so as not to pick up DNA contamination from people who have touched the teeth. A few of the samples contained mtDNA that resembled those of modernPolynesian populations. Although the researchers are fairly confident that their results are accurate, explaining it is more difficult.
One hypothesis suggests that Polynesians could have traveled to the western coast of South America, then made their way east to southern Brazil. However, the group would have had to cross the Andes, which most groups living on the west coast were not believed to have done. Another theory suggests that slave traders could have brought Polynesians to Brazil where they could have interbred with the Botocudo.
(Hat tip to Nature)