DIVERSITY AND AGE OF THE 4 MAJOR MTDNA HAPLOGROUPS, AND THEIR IMPLICATIONS FOR THE PEOPLING OF THE NEW-WORLD

Despite considerable investigation, two main questions on the origin o f Native Americans remain the topic of intense debate-namely, the numb er and time of the migration(s) into the Americas. Using the 720 avail able Amerindian mtDNA control-region sequences, we reanalyzed the nucl eotide diversity found within each of the four major mtDNA haplogroups (A-D) thought to have been present in the colonization of the New Wor ld. We first verified whether the within-haplogroup sequence diversity could be used as a measure of the haplogroup's age. The pattern of sh ared polymorphism, the mismatch distribution, the phylogenetic trees, the value of Tajima's D, and the computer simulations all suggested th at the four haplogroups underwent a bottleneck followed by a large pop ulation expansion. The four haplogroup diversities were very similar t o each other, offering a strong support for their single origin. They suggested that the beginning of the Native Americans' ancestral-popula tion differentiation occurred similar to 30,000-40,000 years before th e present (ybp), with a 95%-cofidence-interval lower bound of similar to 25,000 ybp. These values are in good agreement with the New World-s ettlement model that we have presented elsewhere, extending the result s initially found for haplogroup A to the three other major groups of mtDNA sequences found in the Americas. These results put the peopling of the Americas clearly in an early, pre-Clovis time frame.