Evolution is a theory or scientific notion which conveys the idea that all life in our world has developed over time and continues to change by a process known as natural selection. Every living creature has participated in the evolution of their species, that's right, even us humans. An animal whose evolution goes back as far as 30 million years is our very large furry friend, the bear. Bears are classified in the Ursidae family which includes eight altering species of bears found in habitats across the Northern and Southern Hemispheres (American Museum of Natural History, 2008). In this article, I will reveal the evolutionary path of a very special species - the Kermode bear. The Kermode bear, called ‘spirit bears’ by First Nations, can only be found in the northern islands of British Columbia, Canada, in the world's largest temperate rainforest, the Great Bear Rainforest. It is estimated that less than 400 Kermode bears exist today across the 6.4 million hectares of forest (spiritbear.org, 2019).
First, I want to focus on the evolutionary path of bears. Scientists believe that bears originated as a raccoon sized mammal known as the Miacids (Senckenberg Biodiversity and Climate Research Centre, 2019). As evolution occurred this mammal formed into a larger species known as the ancient Etruscan bear. Etruscan bears were considered to have been originated 5 million years ago with fossils being discovered across Europe, Africa and Asia (a-z-animals.com, 2008). As the Etruscan developed further, two separate species emerged: black bears and brown bears. As of today, black bears are extremely different to their brown bear relatives', splitting from their common ancestor 5.05 million years ago (Science Daily, 2013). The first black bear ancestor is a species known as the sun bear or the Asiatic black bear, who roamed the earth approximately 4.58 million years ago (a-z-animals.com, 2008). The earliest discovered American black bear fossils were discovered in Pennsylvania in 1968 and have been analyzed to significantly resemble their Asian ancestor (Hofreiter M, 2008). Based off these fossils, American black bears can be understood to have shrunk in size today compared to their size around 11,650 years ago (Hofreiter M, 2008). The evolution of black bears was essential in allowing the species to inhabit a variety of ecological niches from arctic ice shelves to temperate rainforests.
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It was around 300,000 thousand years ago the Kermode bear evolved into its species separate from the generic American black bear. Initially discovered in 1905 by zoologist Francis Kermode, the species was classified as a sub-species of the American black bear, Ursus americanus kermodei (spiritbear.org, 2019). What truly makes the Kermode bear so special is how it has evolved to experience a recessive genetic mutation referred to as 'kermodism'. 10 out of 100 Kermode bears experience a single, non-synonymous nucleotide substitution in their MC1R gene, which results in no production of melanin (U.S National Library of Medicine, 2018). Melanin is, “a group of natural dark biological pigments found in most organisms indicating the color of skin, hair, feathers, scales or eyes” (Britannica, 2019). You might be wondering why spirit bears are not classified as albinos? Well, their fur may be white, but both their eyes and noses are pigmented, meaning their species has rather experienced color polymorphism. “Polymorphism is the occurrence of two or more alternative phenotypes in a population of a species” (techopedia.com, 2019).
The evolutionary mechanism of genetic drift was essential to the Kermode bear species as it increased the initial occurrence of the genetic mutation into a frequency high enough that recessive homozygotes were present to be selected. Genetic drift is defined as, “A variation in genotype frequency within a small population with the disappearance of particular genes as a result of an individual's death or inability to reproduce” (Khan Academy, 2019). It has been suggested by researchers at National Geographic that the white fur acted as a camouflage to the bear against the arctic ice and snow during the last ice-age which covered the coast of British Columbia 11,000 years ago (National Geographic, 2015). After the ice-age, Kermode bear populations, who were separated from the mainland by glaciers, are considered to have retained the color polymorphism even after the glaciers receded (worldconservationunit, 2012). Curiously, in 1977 scientists from Oxford Academic found that there was diversity in the mitochondrial DNA of black bears across North America. Two distinct differences in this DNA were separated by the Rocky Mountains continental divide in Alberta, British Columbia and Montana, all contributed to a glacial refugium during the Ice Age. This proves how historical geographical factors, such as the ice age and continental drift caused the isolation of this species, and overall induced genetic drift causing the increased frequency of white polymorphism. It has also been suggested by scientists that the polymorphism provides the animal with hunting and survival advantages. Researchers from the University of Victoria found that spirit bears have greater success when hunting salmon as a result of their white fur (University of Victoria, 2018). Dr. Thomas Reimchen states that, white bears are less visible to fish than their black counterparts, making them 30% more efficient at capturing salmon in the island's rivers (University of Victoria, 2018). Color polymorphism as a result of evolution and genetic drift, provides the Kermode species with hunting and survival advantages both today and thousands of years ago. Another evolutionary mechanism linked to Kermode bear species is assortative mating. “Assortative mating a form of non-random mating in which pair bonds are established based on phenotype” (Britannica.com, 2018). Essentially, white furred Kermode bears when in the process of reproduction and the selection of a mate, have been influenced based on the bears' observed phenotype, likewise with the black Kermode bears. This evolutionary mechanism has increased the frequency of recessive alleles of the mutation resulting in the event of more color polymorphism through the species evolution, this also allowing the species to increase its population.
As Charles Darwin said, “It is not the strongest of the species that survives, nor the most intelligent that survives. It is the one that is most adaptable to change”. As we head into an era of rapid global development, human impact is starting to impose upon even the world's most un-touched areas of wilderness. Canada has been declared to be in a 'climate emergency' with all species across Canada being enforced to adapt and deal with rapid changes in their environment (canada.ca, 2019). Statistics given in the Canada's Changing Climate Report in 2019, have proven that Canada's annual average temperature has warmed by 1.7 c since 1948, with its highest heating rates specifically located in the Prairies and northern British Columbia, the home of the Kermode bear (canada.ca, 2019). For this species to survive for generations to come, it must take a path of developing selection pressures in phenotype to deal with the increased heat. The fur on Kermode bears provides it with heat insulation from cold conditions, although with a heating climate this will become unnecessary. The genome of this species must reflect warmer weather, potentially leading the bear to have thin, little, or no fur. It can also be considered that a major part of the Kermode bears diet, salmon, are also being compromised as a result of climate change. As air temperatures rise across Canada water levels in rivers systems are declining and causing rainfall precipitation to increase, thus causing more frequent flooding during salmon spawning seasons (alliance2030.ca, 2018). These unfavorable conditions are causing the number of salmon returning to rivers to decline rapidly, which in turn, is not supplying a sufficient supply of food for the bears. Therefore, Kermode bears must adapt and shift their dietary regime to obtain sufficient nutrition from alternative foods in the forest. These adaptions must happen soon to guarantee the survival of this species for generations to come. Although, as evolution occurs over extensive time periods, unfortunately the existence of this magnificent species is merely in the hands of the human race.
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