According to a recent study, early indigenous Americans may have come from two distinct populations that both traveled across an ancient land bridge almost 15,000 years ago.
It has been a largely accepted theory that the first indigenous American traveled from present day Mongolia across a land bridge known as the Bering land bridge. Recently however, scientist have been puzzled by contradicting fossil evidence found deep within the Amazon rainforest.
Bone and skull structures of ancient skeletons found among the remote regions of the rainforest matched up with traits found in present day Aboriginal Australians. This finding refuted the theory that Indigenous Americans traveled from a single population budding off of present day Mongolia. However, evidence from bone structures alone are not proof enough to challenge the theory. Similar morphology could be the result of convergent evolution, the phenomenon where distinctly different populations or species evolve similar structures (think birds and bats).
To solve this discrepancy, an international team of geneticists led by Harvard’s Dr. David Reich scoured the rainforest looking for modern day Amazonian tribes. These tribes, which are isolated from the rest of the world, are the closest living relatives to the first Americans. A total of thirty tribes were sampled, including the Surui, Karitiana, and Xavante peoples of the rainforest.
Armed with sixty-three biological samples from indigenous Amazonians, Reich and colleagues scoured their genome to look for conserved evolutionary ‘markers’. These markers, which act as molecular fingerprints for evolutionarily similar groups, were then compared to populations of humans across the globe. Indigenous Amazonians showed related genetic markers with Papuans, New Guineans, indigenous Australians, and other present day South East Asian populations. No other population had markers that match up significantly, not even data from present day Mongolians as predicted from the current theory.
With this new discovery, Reich came up with a new hypothesis for New World migration. One population of humans, related to present day Mongolians, migrated to the Americas roughly 15,000 years ago and colonized most of the New World. Around the same time, another district population followed the same route and colonized the Amazonian area. This Amazonian area split from a population of humans that later colonized the islands of South East Asia.
However, the theory stops there. Many unanswered questions still remain, such as the size and path taken by these two nomadic groups. Perhaps these populations cooperated in their journey to the New World, and occupied separate areas upon reaching their destination. Carbon dating the ancient skeletons found in the Amazonians shows that the Aboriginal Australian migrants arrived in the Americas over 10,000 years ago, painting this possibility. However, without more anthropological data, this mystery remains unsolved.