Ecology
Polar bears have been running on the ice of the north for much longer than scientists thought, recent studies have shown, and probably interbred with brown bears after these two developed individual species.
New research by German scientists has refuted the opinion of other zoologists, who claim that the polar bear separated from the brown bear about 150 thousand years ago. Scientists analyzed the bears' mitochondrial DNA, a special “additional genome” that is only transmitted through the maternal line. They concluded that bears began to belong to two different species about 600,000 years ago.
If polar bears were 150,000 years old, according to a recent study, they would have to develop many of the special skills they have today in a relatively short period of time, German scientists said.
“I've long been puzzled that polar bears were considered a species that evolved so quickly,” said Frank Hailer of the Senckenberg Natural Research Society in Frankfurt/Main. “I kept asking myself, is this really the case?”
The mystery of bear DNA
Hyler and his colleagues studied in detail the nuclear DNA of bears, which is inherited from both parents and is much larger than the mitochondrial genome.
They compared 9,000 base pair sequences (the chemical that makes up the “steps” of a staircase-like DNA molecule) from the nuclear DNA of 45 polar, brown and black bears. This comparison helped scientists build a family tree with the idea that the greater the differences between species, the farther apart they are in their evolutionary development.
“We found that polar bears are much older than earlier studies showed, they looked the way they look today, as much as 600,000 years ago,” Hyler said. – At that time, bears had bears There were more habitats than today, and they were able to evolve in cold climates.”
Adapting to harsh conditions
Researchers reported that 150 million years ago, hybridization may have occurred between polar bears and brown bears, as can be traced from mitochondrial DNA, during the last warm interglacial period. At that time, sea ice began to melt and polar bears had to go to land, where they came into contact with brown bears.
The researchers say this hybridization allowed brown bears to transfer their mitochondrial DNA to polar bears. If brown bear DNA helped polar bears survive in warm conditions, it may have been easily passed from one generation to the next.
It seems that the polar bear population was very small at the time when hybridization with brown bears took place. “The effect of hybridization was very large, so part of the mitochondrial DNA that came from brown bear to white bear replaced the original mitochondrial DNA that the polar bear had,” – Hyler said.