Recently a 14,000-year-old human tooth fragment shows that a large amount of Asians are the ancestors of the first Americans. This tooth was found in Southern Siberia near Lake Baikal and became the oldest known genetic link between the populations. This tooth not only connects Asians to the first Americans but to Native Americans in both North and South American continents. Continually, through further study the tooth can find the origin of its DNA from two separate Asian populations. Cross referencing the DNA of the newly found tooth and previous ancient Siberian sites archaeogeneticist He Yu of Max Planck Institute for Science of Human History in Jena Germany and her team can conclude that one of the populations was from north-central Asia while the other was from northeastern Asia. Further study is need to know why these two populations had came across each other but scientist do know that mating took place between them and their decedents most likely crossed the land bridge to the America continents.
Second Link: https://www.cell.com/cell/pdf/S0092-8674(20)30502-X.pdf?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS009286742030502X%3Fshowall%3Dtrue