THE EVOLUTION OF POLAR BEAR

                                              In present days, Polar bears (Ursus maritimus) are generally found in the Denmark (Greenland), Norway (Svalbard), Russia, United States (Alaska) and Canada. Previously many papers are published about the evolution of the polar bears. Many of them said that polar bears were evolved from the brown bears; the polar bears were separated from the brown bears about 150,000 years ago. There is another theory that polar bears were evolved from the grizzly bears, and they were separated from the grizzly bears about 600,000 years ago. My paper is not about those ideas; rather it is a new concept of the evolution of the polar bears.

BASIC CONCEPT OF MY THEOREM

                                                 My concept of the theorem is that the polar bear was evolved from the cave bears ((Ursus spelaeus). Cave bears lived in the earth about 5.3 million years ago to 11,000 years ago. Now they are extinct. I shall give some points to establish my concept.

HABITAT

                                        The cave bear's range stretched across Europe; from Spain and Great Britain in the west, Italy, parts of Germany, Poland, the Balkans, Romania and parts of Russia, including the Caucasus; and northern Iran. The largest numbers of cave bear remains have been found in Austria, Switzerland, southern Germany, northern Italy, northern Spain, Croatia, Hungary, and Romania. The huge number of bones found in southern, central and Eastern Europe has led some scientists to think Europe may have once had literally herds of cave bears.

                                             Therefore we conclude that, after every generation the number of cave bears were increasing in a high rate or may be in a very high rate. So clearly the next generations need more places for their habitat and diet. So they migrate- Some of them migrate to the northern sides, then at 2.58 million years ago the ice age happened and ice sheets were established in Northern Europe, Antarctica and Greenland. After this they stayed in those icy cold areas.

BODY, SKELETON & PHYSICAL CHARACTERISTICS

                                               Here I’m giving some points for establishing my theory.                                        

The average weight for males(cave bears) was 400-500 kilograms or 880-1102 pounds, and for females (cave bears) was 225-250 kilograms or 496-551 pounds where the weight for males(polar bears) is 350-500 kilograms or 700-1500 pounds, and for females (polar bears) is 150-250 kilograms or 330-550 pounds. The most important point to be noted that, in the cases of both bears we can see the weight ratio of the males and females is 2:1.

If we compare the skeletons of the cave bears and polar bears, then we can find that skeletons are very similar.

The cave bears had a very broad domed skull with a steep forehead. Now if we study the skulls of the polar bears we can see they also have a very broad domed skull with a steep forehead.

      

ADOPTATION OF POLAR BEARS

                                        We know that polar bears have a great adaptation history.  Here are they-

SMALL AND ROUNDED EARS- Polar bears have small and rounded ears which help them to prevent the cold water from entering the bear’s ears and freezing their eardrums. This also helps conserve body warmth in sub-zero temperature.

LONG STIFF HAIR BETWEEN PADS OF THE BEAR’S FEET- It protects their feet from the cold and provides traction on the ice. It helps them to swim in the cold icy water and also helps them from slipping on the slippery ice. Their hair usually shakes free any water on ice formed after swimming.

HOLLOW FUR- It traps air inside, thus making the bear buoyant in water. The layer of air provides insulation between their warm bodies and the cold Arctic air & water. Insulation provided is lost when fur is covered with oil.

THICK LAYER OF FAT (BLUBBER) UNDER SKIN- It is up to 11 cm thick. It insulates bear from Arctic cold. Though it make some problems also. It causes the overheating. To prevent in warm days or after some physical works. If they are over heated, they release the heat from the body through areas where fur is absent or where blood vessels are close to the skin. Examples- muzzle, nose, ear, foot, pads, inner thighs, shoulders.

SKIN UNDER THE FUR IS BLACK- This is to ensure that the polar bear has a better heat retention rate.

                                        So we arrived to the vital question, that how this huge evolution happened within a very short time of period (respect to the evolution history).

                                        Here it’s my theory about that evolution- The population of the cave bears getting larger and larger, now from the theory of Charles Darwin we conclude that, over population creates the insufficiency of food and habitat: resulting in struggle for existence. So the relatively weak group/groups of cave bears have to migrate to other places for food and habitat. In this migration, one or more than one group migrate to the northern side of the Europe, the Antarctica and Greenland. They started their journey of life there. Then about 2.58 million years ago the ice age happened, and the whole Antarctica, Greenland and the northern Europe completely covered with ice. Permanently great ice sheet established there. Clearly that was not a favourable condition for living.  Now, as the time passed, their population getting higher again and they faced the problem of insufficient food and habitat. The climate is already against them. So these occurs,

Over population + natural destruction à struggle for existence

Struggle for existence+ confinementà  balance of nature

Balance of nature + change in conditionà struggle for existence

Struggle for existence+ beneficial variationà natural selection

Natural selection+ time à speciation

Explanation:

                                   As the time passed the population of those group of cave bears were getting larger and larger, and in the other hand ice covered the whole lands. Clearly the nature was against them. So, over population and natural destruction causes struggle for existence.

                                 This struggle for existence and their confinement in the in Northern Europe, Antarctica and Greenland causes a balance of nature. As the ice sheets completely disjoint the Northern Europe, Antarctica and Greenland from the world, so a completely new and separated eco-system created there and this was balanced.

                                 In this new eco-system some changes happened in the physical condition of the cave bears. These changes in physical conditions and natural conditions of cave bears cause changes in the organic conditions of the cave bears. So after some generation there exist cave bears whose physical and organic conditions are not the same. So in the new eco-system there exist cave bears with different variations. In the way of life it causes another struggle for existence.

                                  This struggle for existence was about the existence of the better mutating cave bears. So in this fight of existence the beneficial variation wins. That is, those cave bears whose variation were favourable in those conditions were selected by the nature

                                  The chosen variation of the nature only survives there and others were extinct. Thus as the time goes that chosen variation created a new species. The species called polar bear.

DIET –

                                   The morphological features of the cave bear chewing apparatus, including loss of premolars, have long been suggested to indicate their diets displayed a higher degree of herbivore than the Eurasian brown bear. Indeed a solely vegetarian diet has been inferred on the basis of tooth morphology. Results obtained on the stable isotopes of cave bear bones also point to a largely vegetarian diet in having low levels of nitrogen-15 and carbon-13, which are accumulated at a faster rate by carnivores as opposed to herbivores. However, some evidence points toward the occasional inclusion of animal protein in cave bear diets. For example, toothmarks on cave bear remains in areas where cave bears are the only recorded potential carnivores suggests occasional cannibalistic scavenging. So we conclude that the cave bears were omnivorous, or at least they were not completely vegetarian. Therefore when it is necessary, they can be carnivore.

                               Now we all know, polar bears are completely carnivorous.

       Now here is my concept about the evolution of cave bears into polar bears-

                                      After the glacial period, they total northern Europe, Greenland and Antarctica completely covered with ice sheet. So the temperature went too low, and all the plants died. So the only thing for diet remains, were animal proteins. Since cave bears were omnivorous, they had no problem for taking animal protein for diet.

WHY POLAR BEARS ARE NOT EVALUATED FROM GRIZZLY OR BROWN BEARS-

                                       According to my theory, polar bears came to earth about 1.5 to 1 million years ago. And they came from the cave bears. Whereas grizzly bears are very junior to them. The brown bears came to the earth almost at the same time of the time of the polar bears. Now we know at the ice age period the arctic sea was completely frozen. Now I believe, at that time some troops of the brown bears migrate there, and they entered the territory of the polar bears. There those two different types of bears met to each other. And after breeding they started a new species, its grizzly bears.

                                      Now from the concept of heredity of Mendel, we know that the characteristic of the paternal and maternal genes take part in the time of breeding. Now grizzly bear were the half-breed of the polar bear and brown bear. Hence in the DNA of grizzly bear some characteristic of brown bear and some characteristic of polar bear dominant there.

                                      Scientists find that the mitochondrial DNA of polar bear is very much similar to the mitochondrial DNA of grizzly bear, so they consider the fact that polar bears evolved from grizzly bear. Though I believe, grizzly bears are evolved from the polar bears.

                             Hence polar bears are evolved from the cave bears.