Evolution Essay

Did this last year tell me what you think!

            It can be argued that human beings are currently increasing the evolutionary rates of many animals on Earth.  Through acts such as polluting, displacing animals from their habitats,  and the use of chemical pesticides humans have caused sexual selection, mutation, and “natural selection” to occur at alarming rates within animal populations.  Notable examples of such animal species being affected include the polar and grizzly bear populations, insect populations, and the cane toad populations.  Increased human influence on animal evolution must be closely monitored in order to prevent the immoral extirpation and extinction of certain species.


            Two species’ evolutions that have been affected by humans indirectly, and should also hit close to home for Canadians, are polar bears and grizzly bears.  Human influence via air pollution that has in turn led to global warming is causing changes in the sexual selection of the two species and the speciation of new hybrids known as pizzlies.  This is affecting biodiversity within polar and grizzly bear populations, and may lead to the extinction of the species.  The warm weather and melting of glaciers that has occurred due to man-made holes in the ozone layer of the Earth’s atmosphere has allowed or in the case of the polar driven these species closer together.  Due to climate, polar bears are losing their homes and moving inland meanwhile grizzly bears have been allowed to journey farther North then ever before to search for food.  These bears have adapted to their new environments and as such are now mating.  This is a stark comparison to normal encounters that these two bear species have been known to have in the past which are commonly aggressive.  The offspring of these two species, the pizzly, was long thought to have been merely a rumour until as recently as 2006 when scientists and hunters began to confirm a fairly large population of the animals.  What shocks scientists the most is the frequency of pizzlies being discovered, as hybrids like these although not unheard of are usually just very rare oddities in nature, not a trend.  Scientists are worried that the speciation of polar bears and grizzlies will disrupt the biodiversity of the two separate species.   Previous data that has been collected pertaining to hybrids within a population has shown that as the number of hybrids increase, the number of founding species will decrease until it is possible that only hybrids remain.  The former could also lead to the extinction of the two species, as these hybrids are born sterile due to their post zygotic isolating mechanisms and are not enabled to pass on their genes.  In other words the species may eventually die out if the majority of the population consists of hybrids.


            Another way that humans have affected the evolution of animals is through the use of various chemical pesticides often used to kill vermin and insects, in order to protect crops, livestock, and human beings. The most notable cases of pesticide spurred evolution are in insects that include bed bugs, mosquitoes, and the notorious head lice.  These species of insects have adapted and mutated to overcome insecticides through various manners in order to survive. The first perhaps most radical example of this is in bed bugs.  They have evolved to combat not just one but several insecticides that have been used to eliminate them from surfaces and fabrics.  Scientists have observed that new bed bug generations have obtained their resistance through the passing of genes that allows individuals the ability to coat their exoskeleton in a biological wax like substance that acts as a shield from harmful chemicals. The mosquito has formed its own solution to combat the toxic pesticide DDT which was once used in some countries as the prime method of dealing with mosquitoes despite its potent effect on the environment.  Mosquitoes have evolved to now exhibit and pass down a tolerance to DDT.  Although DDT is shown to repel mosquitoes it is no longer killing mosquitoes like it has been for years.  Head nice in certain parts of Britain have been observed producing an enzyme that is nullifying chemicals such as carbaryl which are used to kill and wash lice out of ones hair. It is unclear as of now why only lice in certain areas are producing the enzyme but as with all the resistant insects being discovered currently, is certainly counter productive to the purpose of the pesticides in the first place.


            Finally, the introduction of alien species to new environments by humans has not only had the intended effects of controlling certain species populations, it has also yielded unintentional evolutionary consequences. A prime example of this is with the cane toad which evolved into an excellent hunter, practically disease free, and adaptable super toads following their introduction to the Australian wilderness.  Originally though as an organic means of pest control the cane toad was introduced to Australia in order to control their beetle population.  Unbeknownst to scientists, the toad would evolve to dominate the environment by becoming supreme hunters.  New generations of toads were being born consistently and breeding consistent larger and faster toads that broadened their scope of prey to larger insects and even small reptiles. Scientists have also observed that the toads are no longer passing on parasites and genes that cause common diseases within the species and as such are sustaining a much larger population then ever before. Finally, and most disturbingly, the cane toads are now also being observed adapting to different harsh, dry environments within the Australian wilderness that they have never before encountered such as the outback. Scientists can only speculate what other traits the toads will evolve to possess in the future and how other species may evolve to compensate for their presence in this dramatic case of directional selection.


            It is important to remember that as the dominant species on Earth humans have to respect the balance of nature. Though sometimes unintentional the acts of humans have caused evolution to occur within species at a rapid and arguably unhealthy rate for the environment. These changes are sometimes behavioural, physical, and even sexual but are all caused due to a need in animals because of circumstances humans have put in place.  Whether they are for the good or bad of Earth or perhaps a mixture of both only time will tell, perhaps quicker than expected.



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