Theorigin of polar bears ( Ursus maritimus )as an independent species took placeabout 600,000 years ago, as revealed by an international investigation in which the Higher Council for Scientific Research (CSIC) has participated. Its evolutionary history is, therefore, five times older than previously believed, as published in the magazineScience.
Previous studies had found similarities in the mitochondrial DNA, coming from the mother, between polar bears and brown bears (Ursus arctos). Because of this, it was assumed that the Arctic species belonged to a split lineage from its brown cousins between 166,000 and 111,000 years ago and that it had undergone rapid adaptation to polar conditions.
The new research has been based on the analysis of nuclear DNA from 19 specimens of polar bear, 18 specimens of brown bear and seven specimens of black bear (American bear). The differences detected between the genomes indicate that the polar and brown species diverged from a common ancestor about 600,000 years ago. ? The similarities between the mitochondrial DNA of the two species could indicate the hybridization between brown females and polar males, whose offspring were integrated with the polar population ,? explains Jennifer Leonard, a researcher at the CSIC’s Doñana Biological Station.
The new finding represents an evolution much more similar to that of the rest of the arctic mammals. Leonard is of the opinion that her specific adaptations, such as her white hair, black skin, and the wrapping of her feet, are now less surprising. The polar foxAlopex lagopus), for example, split from its original lineage about 900,000 years ago.
The belief that polar bears had evolved in a period between 166,000 and 111,000 years assumed that this species had a high adaptive capacity to polar conditions. This paradigm shift suggests thatcould be much more sensitive than previously thought to the possible effects of climate change. This species is not only facing disappearance from its habitat due to glacial melt. Leonard explains that this fact forces them to “colonize regions inhabited by humans where their survival is compromised.” “If we lost the polar bear in our era, we should ask ourselves to what extent we have hindered their survival, since they were clearly able to withstand other warmer times in the past,” he adds.
