This has been a topic of scientific discussion for some time but now a new study clarifies things a bit. The study shows that the two species actually began to separate about 1,5 million years ago. What is striking to researchers is that the bears continued to interbreed frequently for quite some time.
This makes their history more like human history. Human evolutionary history is no longer thought to be linear bur much more complex with breeding and interbreeding among many separate populations. Brown bears swimming to isolated polar bear populations are now thought to have brought much-needed genetic diversity to the polar bears.
A startling discovery is that most of the introduction of new genetic material into polar bears has come from brown bears. The study was based on the genetic material from 64 modern polar and brown bears. Genetic material from a Norwegian bear which lived over 100,000 years ago was also sampled.
In fact polar bears are now thought to have undergone several population bottlenecks. Introduction of new genetic material from brown bear populations has happened more than once. Polar bears have undergone many superficial changes over the years. They have become smaller, their body shape has changed and their ears are smaller. The most striking adaptation is their white appearance. Their skin is actually quite dark but the hairs on their body have adapted to reflect the colors of the surroundings, which are usually white. They can, however, look reddish at sunset.
The recent study was conducted by scientists and the University at Buffalo. It was published in the Proceedings of the National Academy of Sciences. Advances in genetic science have led to numerous discoveries regarding animal evolution. A recent paper on Australian dingo evolution was discussed here.