Origin: A Genetic History of the Americas

Native Americans) (5).
This split between NNA and SNA branches tell us a lot about the initial
peopling of the Americas. For one thing, most genetic evidence indicates
that the split took place south of the ice sheets, because representatives of
the Ancient Beringians (Trail Creek Cave and Upward Sun River) are
equally related to members of the NNA and SNA groups. If those groups
had split before they left Alaska, it’s likely that one or both groups would
have intermarried with the ancient Beringians, resulting in ancient
Beringians being more closely related to one branch or the other.
We also see confirmation of this split and its timing from the
mitochondrial genomes of dogs.
Dog mitochondrial genomes rapidly diversify into the four lineages
found in ancient North American dogs iii at nearly the exact same time as the
NNA/SNA split: about 15,000 years ago. With the caveat that these
mitochondrial data show us only a small fraction of dog population histories
in the Americas—the edge pieces of the puzzle—the radiation of dog
lineages that mirrors human lineages is nevertheless extremely strong
evidence for this model (6).