Some good points made here lads, as LFC1 said, I too saw this program with this tribe deep into the amazon forest (not too sure where exactly as I know the Amazon is massive and covers a lot of ground), and when the team (tv team that is) went out there it was the first outsiders to meet them since the early 30's.
They had this proper mad language that goes back hundreds of years and hardly anyone can decode or translate it!! It was an excellent program, and some of their techniques were amazing.
For example, they used to cut into trees and get this salt type substance from inside the root of the tree and then tey would sprinkle this into a part of the river, and within seconds all the fish floated to the top of the water (dead), as the salt substance took all the oxygen out of the water. This is just one example but they had loads of techiques, I mean if you saw the accuracy they had (with a bow and arrow, that they laced with poison) in killing tiny birds more than 70ft into the canopies, it was really amazing.
So I think these type of tribes (though not as widespread anymore) are probably the only ones left in the world that have a chance to be 'pure' in the genetic sense!!