Polar Bear Evolution – How Did Polar Bears Evolve?
How did polar bears evolve? Ursus maritimus, better known as the polar bear, comes from the animal family known as Ursidae and is the one of the largest species of bears of the planet. A carnivorous predator 38,000,000 years in the making, the earliest evidence of the modern polar bear dates back roughly 110,000 years.
Many researchers believe that their evolution stems from brown bears that were isolated in arctic climates of the far north during the Pleistocene, more commonly referred to as the Ice Age. This coincides with fossils of a polar bear’s jawbone that were discovered near Norway in 2004.
This geographical separation played a big part in polar bear evolution as the bears had to adapt to the extremely cold environment in a number of ways.
When compared to the grizzly bear, polar bears have larger feet and tougher claws to facilitate better traction on the ice as well as digging into the ice to build dens for shelter. A thick layer of fat under the skin, coupled with two layers of fur, enables them to stay warm in arctic regions they call home.
A good portion of polar bear evolution was dedicated to keep warm in the unforgiving arctic. In contrast to their trademark snowy fur, the skin of the polar bear is actually black.
Black acts as a heat insulator as it literally absorbs all color wavelengths. In spite of the extreme cold, the Arctic Circle sees it’s fair share of sunlight and the bears soak it in. While first glance would have you believe the fur to be white, it is actually clear.
White is the opposite of black, in that it reflects all light. Having fur that bounced the light off of you would be very disadvantageous. Instead, the hairs on a polar bear are clear and hollow.
This allows sunlight to reach the skin and it also gives the fur its white appearance to work as camouflage. In addition to braving the arctic winds, the polar bear has to contend with arctic water as well.
Having to swim for their dinner was a major factor in polar bear evolution. Unlike most species of bear, which are omnivorous, the lack of plant life in the arctic led to polar bears becoming purely carnivorous, and a large portion of the polar bear’s diet is aquatic.
This in turn led to them becoming adept at swimming in order to catch their prey, averaging a speed of 6.2 mph in the water. For reference, Michael Phelps clocks in right at 6 mph! They developed extra eyelids to see underwater, similar to alligators.
In order to further regulate their temperature under water, the polar bear developed smaller ears that flatten when they swim to minimize heat loss. Even their noses close up to avoid water intrusion as they swim under the ice.
In the overall scope of life on Earth, the 480,000 years it took for polar bear evolution to become what it is today is very impressive. Looking beyond the external changes that the species has undergone, we still see evolution at work.
The change in diet had an impact on the genetic level. Specifically the apolipoprotein B gene, or apoB gene for short has mutated greatly. This gene affects how mammals metabolize LDL cholesterol, which is often referred to as “bad” cholesterol.
In humans and most other mammalian species excessive LDL cholesterol can lead to cardiovascular health issues. However, the marine animals that polar bears eat contain high amounts of blubber.
This means that the mutation to the apoB gene allows polar bears to live off a high-fat diet with the risk of cardiovascular disease.
With all these environmental and behavioral adaptations that the polar bear has developed., it is easy to forget that the polar bears are still descendants of brown bears. An article printed in Conservation Biology, in 2008 by Lisette P. Waits, talks about mitochondrial DNA of the North American Brown Bear.
Looking at mitochondrial DNA of the brown bear and polar bear, scientists found distinctly different genetic patterns. However, mating between brown and polar bears has resulted in fertile grizzly-polar bear hybrids in nature.
Polar bears are the product of their environment. If not for the isolation caused by the Ice Age, this species may not exist at all. The question, “how did polar bears evolve?” is a topic that is still examined to this day due to the level of adaptation brought about by natural selection, as it was entirely possible that the bears that were stuck in that cold, unfamiliar environment could have succumbed to the drastically different climate.
Polar bear evolution is especially prevalent given the current state of their deteriorating habitat. Given that evolution is an ongoing process, it is entirely possible that the polar bear will continue to evolve as the world changes in order to survive.