Evolution of Polar Bears and Brown Bears

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by connorj51999
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Discipline:
Science
Subject:
Animals
Grade:
8,9,10

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Evolution of Polar Bears and Brown Bears

The Evolution of Polar Bears & Brown Bears

The Divergent evolution of Polar bears and Brown bears was caused by the process of natural selection. Firstly the word Divergent means that the common ancestor split into new species. In this case the common ancestor, the Brown bear, split into two species; the Polar bear and and still kept the Brown bear species. Natural selection is the engine that drives evolution. It works to produce the most amazingly diverse range of life forms on the Earth today. Natural selection is when evolutionary change occurs through the variation between individuals of the same species. Some variants give the individual a better survival probability by giving it new features to improve its chance of survival. This makes the new individual split from the population, essentially evolving into a new species. This is caused by many factors such as changes in physical and chemical environments, competition for resources and many other factors.

Similarities- Both diverged from the same ancestor. In this case only part of the Brown bear ancestor's population evolved.- Very closely related genetically even though physically they appear very different physically.- Both are huge in size and weight.- Both have very similar behaviour.- They both are naturally very good hunters and use primarily their powerful noses to hunt their prey.- They are so closely related that they can interbreed and produce fertile offspring that can be found in the wild.-

One of the Brown bear subspeciesUrsus Arctos

The Polar BearUrsus Maritimus

Differences- Polar bears inhabit arctic waters and snow whereas Brown bears inhabit temerate regions of Asia, Europe and North America.- Polar Bears are snow white to yellow in colour whereas the Brown bear has a silvery-brown coat.- Polar bears are strictly carnivorous, but Brown bears are omnivores.- Brown bears are very territorial, but Polar bears are not.- The Polar bear has a longer skull compared to the skull of a Brown bear.- Polar bears have larger feet with little rough dots called papillae and have smaller claws. Whereas the Brown bear has smaller feet, no papillae and larger curved claws.- Brown bears are nocturnal whereas Polar bears are not.- The Polar bear is large than many Brown bear subspecies, but the Kodiak subspecies can sometimes be larger.-

What was the cause of evolution?During the last Ice Age, due to the increasing amounts of ice, the common ancestor the Brown bear was pressured to either stay and adapt to the new habitat or move to a new area away from all the snow and ice. Only the stress-tolerant bears out of the ancestor population were willing to try the new habitat, this is why only part of the population evolved. So the selection meckanism was due to habitat change and stress tolerance. The offspring of the evolving species or early colonizers began to develop piebald colouration (white spotting). The offspring begin moving towards coastlines and developing a diet for seals. The descendants become a new species because of the gene for stress intolerance had been left behind and the 'piebaldness' intensifies over time making the new species fully white, not albino but one big spot. The new species adapted very well physically to move on the ice and live in the colder climate. They became reliant on ice for hunting their prey, therefore they moved further North and towards the coastlines.

How long ago did they diverge?There are many arguments in relation to this question. Some scientists say that they diverged millions of years ago, but more recent studies suggest that they diverged in the last Ice Age about 500 000 years ago.


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