The Evolution Of Canadian Bears - Nepean High School/biology - Essay

1167 words - 5 pages

The Evolution of Canadian Bears:
Small Changes and Environmental Factors lead to Great Changes over Time
The kangaroo is exclusive to Australia. The ostrich is native to Africa. The majority of
prominent mammals have a distinct and recognizable territory, but there are few mammals who
are as prevalent across the globe as the four-legged creature of family Ursidae: The bear.
Evolved from early canids 20-25 million years ago, Bears have covered the majority of
continents for thousands of years, which in the process, has seen its population speciate into
eight immensely distinct species. From the spectacled bear of South America to the polar bear of
the Arctic, the bear has speciated as a result of both natural and artificial selection, as well as
numerous environmental changes.
Bears are present on four of the seven continents, and due to their evident ecosystem
diversity, they have speciated into eight extant species. Of family Ursidae, there are three
subfamilies: ​Ursinae, Ailuropodidae and Tremarctinae. Subfamily Ursinae consists of the closest
relatives to the Canadian brown bear, including the polar bear and the American black bear. The
polar bear speciated from the brown bear as early as 150,000 years ago, yet the polar bear may
not be considered a species under some species concepts. There have been cases of mating
between the brown bear and polar bear in the past to produce a hybrid, and the likelihood of this
happening is on the rise as the habitats of the two species approach each other due to climate
change in the arctic. The biological species concept would state that they are the same species,
due to their ability to mate under natural conditions. Although this example of hybridization is
the only recent case, it has been proven that mating between two seperate bear species has
occurred for millennia in the past. Studies have revealed evidence of substantial gene flow
between species, with 8.8% of selected extant brown bears shown to have polar bear ancestry,
despite polar bears being descendants of brown bears. However, the evidence of hybridization is
not exclusive to brown and polar bears, the bering land bridge allowed for habitat isolated bear
species to hybridize. This gave a chance for the brown bear from North America to mate with the
asiatic black bear of Asia, an example of genetic drift. The bridge was submerged approximately
14,000 years ago, resulting in zero to no gene flow between species, due to habitat isolation. In
their own environments, bears have become structurally, behaviourally and genetically diverse
from their relatives.
Split from early dog-like creatures (canis) about 20-25 million years ago, bears are
believed to have been diverging into separate species for the past 20-25 million years. With their
habitats so contrasting to each other, each species has adapted and evolved to suit their
ecosystem, some faster than others. Random mutations in the gene pool can result in a selective
advantage ...

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