The Evolution of Polar Bears

In this essay I will be talking about The ‘Evolution of Polar Bears from Brown Bears, specifically skin and fur colour, skull and ear shape, and digestion of seal fat’ ill also talk about the two theorists Jean-Baptiste Lamark (1744-1829) and Charles Darwin (1809-1882).
Charles Darwin’s theory states that the change in evolution is the variation in each generation and different individual surviving features with different combinations of the variable. The Individuals with characteristics that increase their probability of survival will be able to reproduce more often and their offspring will also benefit as there would be an advantage because it would be passed on to the offspring. Over time these variation of characteristics will spread through the population. (College, 2009)

Jean-Baptiste Lamark believed individuals had to change their behaviour to survive. If they began to use an organ more than they had in the past, it would increase in its lifetime.
For example: If a giraffe stretched its neck for leaves, for example, a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit the longer neck, and continued stretching would make it longer still over several generations. Meanwhile organs that organisms stopped using would shrink. (Dennis O'Neil)

Polar bears and brown bears are genetically closely related. This is evident from similarity of both species DNA and their their structure. Another indication of the close relationship between polar bears and brown bears is the fact that they can interbreed and produce crossbreed offspring. (poler bears and brown bears).
In the extensive glaciations of the northern hemisphere, about 100,000 to 250,000 years ago the Arctic region was warmer and occupied by the ‘Kodiak brown bear’. This was a population of brown bears with many variations of brown just as today's bears have dark fur and light brown fur. Evidence from geology shows that the climate changed during the extensive glaciations, the climate shifted colder to enter an Ice Age. Glaciers eventually trapped a population of bears in the coastal region with an arctic environment. As the ground gradually spent more time covered in snow, bears had an increasing advantage during the leanest parts of the season. The dark-furred bears had a harder time blending into the icy environment while hunting. Pale bears appear with a growing occurrence in the new generations continuing to shift. Mutations and genetic changes constantly occur in reductive replication so new alleles for genes happen in the population. Any new alleles for less pigmented fur colour were promptly favoured. Instead the skin is dark to absorb the heat that passes through the clear hair. The skin still acts to keep body heat trapped in still air. Today, the only bears that are left in the Arctic are bears with unpigmented hair because they live in a mainly white environment. However other genetic changes were also selected as the climate changed, it wasn’t just fur pigment levels that changed. Much larger polar bears survived because they were better at storing heat and they spent less energy to keep warm. A wider paw was selected because it improved support while walking on snow, wider pawed bears hunted with less energy when walking. Bears with narrower heads suffered less resistance when swimming. Bears storing a layer of adipose (Animal fat) for insulation and buoyancy used less energy. Energy efficient bears generally left more offspring with this processes and function of an organism, a detailed analysis or inherited behaviour. (S.R, 2008) (Gunderson, 2009)

http://www.studymode.com/essays/Evoloution-Of-Polar-Bears-Lamarck-Vs-1718444.html