Shapiro’s Nature Ecology study also focused on what may have happened to other polar bear genomes during periods of low ice—in this case, around 120,000 or 125,000 years ago when, according to Shapiro, Arctic ice levels were similar to the present day’s. But here, she looked at the relationship between polar bears and brown bears.
Her team constructed a phylogenetic tree—sort of like an evolutionary map showing how the bears diverged from a common ancestor over time—using Bruno’s genome and those of currently living polar bears, brown bears, and a black bear. (Shapiro was able to utilize one of Laidre’s Southeast Greenland polar bear genomes in her analyses, although the
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