Sources
http://www.nwf.org/wildlife/wildlife-library/mammals/polar-bear.aspx
http://www.pbs.org/wnet/nature/episodes/arctic-bears/how-grizzlies-evolved-into-polar-bears/777/
http://endangeredpolarbear.com/polar_bear_habitat.htm
http://seaworld.org/en/Animal-Info/Animal-InfoBooks/Polar-Bears/Adaptations
http://www.polarbearsinternational.org/about-polar-bears/essentials/evolution
http://www.livescience.com/27910-polar-bear-divergence-brown-bear.html
http://www.bbc.co.uk/news/uk-scotland-highlands-islands-13965286
http://www.pbs.org/wnet/nature/episodes/arctic-bears/how-grizzlies-evolved-into-polar-bears/777/
http://endangeredpolarbear.com/polar_bear_habitat.htm
http://seaworld.org/en/Animal-Info/Animal-InfoBooks/Polar-Bears/Adaptations
http://www.polarbearsinternational.org/about-polar-bears/essentials/evolution
http://www.livescience.com/27910-polar-bear-divergence-brown-bear.html
http://www.bbc.co.uk/news/uk-scotland-highlands-islands-13965286