Polar bears are far more ancient than even the most recent estimate of 600,000 years old, an international research team announced on July 23. They split off from brown bears at least four million years ago—maybe even five—and their numbers have risen and fallen as the earth cooled and warmed, respectively.
Moreover, data from a full genome study—as opposed to the partial one that unearthed the 600,000-year data in April—show that climate change is reflected in the evolution of this animal whose visage has become synonymous with global warming, and suggests that the species has been declining for the past 500,000 years.
Researchers at 13 institutions on three continents, led by Pennsylvania State University and the State University of New York at Buffalo, conducted the most comprehensive analysis yet of polar bear DNA and found that polar bear numbers appear to have fluctuated in tandem with key climatic events over the past million years, according to a statement. In all, the genomes of 28 bears were analyzed, the statement said, with DNA samples supplied by the U.S. Geological Survey and the Norwegian Polar Institute.
The research team’s members were from the U.S., Canada and Mexico, as well as Europe and Asia. Their results were published on July 23 in the journal Proceedings of the National Academy of Sciences.
The genomes provided evidence that the number of polar bears increased during cooler times and decreased during warmer, the statement said, an indication that their habitat probably overlapped with that of other bears when things heated up.
It trumped the study that put the species’ age at 600,000 years because it examined more DNA segments than that one did.
“We showed, based on a consideration of the entire DNA sequence, that earlier inferences were entirely misleading,” said Webb Miller, a Penn State professor of biology and computer science and engineering and one of the study leaders, in the statement. “Rather than polar bears splitting from brown bears a few hundred thousand years ago, we estimate that the split occurred 4 to 5 million years ago.”
Interbreeding between polar bears and brown bears since the two species split from one another most likely explains the murky age estimates, the statement said.
Such findings could be significant when it comes to climate change predictions, said Charlotte Lindqvist, the study’s senior author and an assistant professor of biology at SUNY Buffalo.
“This is the first time we can see, from their genes, how the population history of polar bears tracked Earth’s climate history,” Lindqvist said. The data show not only an increase in polar bears about a million years ago, during a cooling period, but also indicates what she called a continuous decline in their numbers during warmer eras, she added.
“We also found, perhaps unsurprisingly, that polar bears occur in much smaller numbers today than during prehistory,” Lindqvist said. “They have indeed lost a lot of their past genetic diversity, and because of this, they are very likely more sensitive to climate change threats today.”