Population testing is still being done. Some Native American groups that have been sampled may not have shared the pattern of markers being searched for. Geneticists acknowledge that DNA testing cannot yet distinguish among members of differing cultural Native American nations. There is genetic evidence for three major migrations into North America, but not for more recent historic differentiation. In addition, not all Native Americans have been tested, so scientists do not know for sure that Native Americans have only the genetic markers they have identified.