There is a conflict in thoughts of two study groups with regard to Americans settlement. One group supports the established thinking that first Americans had descended from Eurasian tribes that had passed an ancient land-ice bridge between Alaska and Russia. Another group of researchers has directly challenged this idea.

Researchers from Harvard University representing the second group have affirmed that there is a working model present in archeology and genetics showing that most Native Americans today are from a single wave of expansion south of the ice sheets. But it is not correct.

Prof. David Reich said they had missed something very important. The researchers sampled 30 largely isolated native tribes living in Central and South America. The researchers were surprised to know that the tribes in the Amazon rainforest had produced a different Australasian signature. Other tribes revealed ties to Papua New Guinea and the Pacific Islands.

Lead researcher Pontus Skoglund said, "Most genetic studies to date have basically found that all North and South Americans come from a single ancestral source population. That's not what we found".

For now, it is not known when and how this migration took place. But the researchers have stated that the legacy of the group depicted as Population Y is quite strong. Of all, the Tupi-language speaking Surui and Karitiana tribes and the Ge-speaking Xavante of the Amazon rainforest were more closely related to Australasians.