Sunday, March 29, 2009
Are we evolving yet?
In page 58, Sean Carroll says " the rate of mutation has been carefully studied in many species, In humans, there are an estimated 175 new mutations among the 7 billion DNA letters in every individual" (58) It seems like DNA of humans are changing every seconds. Human population is keep rising and there are 6.7 billion of us right now. However, we hardly notice any changes. It seems like evolution has stopped for humans. We can easily see the process of evolution in rats or birds (ex)pg.55). Discuss promoting factors and limiting factors for evolution and explain why humans have stopped evolving. Surely, mutations are keep occuring, but why aren't we getting picked on by natural selection? You may need to explain carrying capacity and factors that maintain carrying capacity. Expalin how carrying capacity of humans differ from other animals and compare factors that maintain carrying capacity with factors that promotes evolution. On the other hand, you may prove that humans are keep evloving and that there are no organisms that completely stopped evolving. Use specific examples to support your arguments.
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Humans have evolved so much that instead of evolving more and more to meet the new demands of geographical and environmental changes, they just create a new device or tool to help them cope with the change. Humans are relying less on change, but more on creativity and innovation to help us meet our new demands. This happens because the human brain enabled us to make tools, farm products, and civilize so we can work on improving our chances by creating things to help ourselves; and not improve our chances by completely changing us. The reason we see many more changes in birds and rats because they create much more offspring and reproduce more. This means that there are more chances for mutation to occur and for it to be picked to help the species evolve from it. The mutations occurring in birds and mice are creating more profound changes than in humans. Humans have a large system with many checkpoints to make sure that the mutations are limited and do not create a damaging change. As well during gentics there are multiple codes for the same protein and that could be causing changes to be kept smaller. In humans if there is truly a large change the human would be taken care of and given treatment so that it would fit in with the rest and be healthy even though it could eventually lead to something good or a change of the population. The carrying capacity of many animals is often restricted to the area they live in and the abundance of abiotic and biotic factors in the are to help it survive and reproduce. Humans have created many tools that have enabled them to manipulate many of the abiotic and biotic factors thus increasing the carrying capacity of humans. Agriculture has become more efficient and if a human is allergic to something or is unable to get a nessacery vitamin or nutrient there are tablets that enable that human to get it in good amounts. Humans do not need to change anything they just improvise and create tools to meet the demands while other animals need to change or adapt some unique way to help meet the needs to the environment and its changes.
ReplyDeletePromoting factors and limiting factors generally tend to be extremely important in the animal world. If we look at wolves, for example, they can be limited by the amount of food available to them and when there is not enough, they stop reproduction because a lack of energy to do so. Humans may have stopped evolving because we don’t really have any limiting factors. We are able to reproduce almost anything we need. If we need more food, it can be easily obtained by a quick drive to the store and some money. There really are no limiting or promoting factors for humans because we are intelligent enough and have the means to obtain anything and everything we need. Not everyone is dying as would be expected in the animal world because we have doctors and technology. This would bring us to the biological theme of science, technology and society. We have been able to ignore the evolutionary changes or stop them from happening because our technology has grown so much that we do not really relate as much to the natural world. We do not depend on dominance or a hierarchy to obtain food. Unlike wolves, who in a pack, establish a hierarchy and the weaker ones will go without food. Essentially, humans have life so easy and we have everything handed to us. Mutations do keep occurring, but we can adapt our medicine or our technology to be able to have the mutations not affect us as much. On the other hand, cancer is a mutation. Cancer kills people (as if we didn’t already know that! ;) Anyway, cancer is a mutation in a cell where the cell does not have the ability to stop dividing. At this point, tumors occur and can many times become cancerous or cause numerous other problems in a person’s body. Also, there are some mutations that really do not affect people’s survival rates. According to an article, blue-eyed humans have a single common ancestor. A genetic mutation that affected the OCA2 gene in our chromosomes resulted in a created of a “switch” which literally turned off the ability to produce brown eyes. This OCA2 genes codes for a P-protein which is involved with production of melanin. Melanin is the pigment that gives color to much of our body parts, such as our skin or our eyes or hair. The gene “switch” though, is not black or white. It does not either turn off the gene completely or leave it on. Rather, it limits the gene’s action which turns the person’s eyes from brown colored, to blue. It really “dilutes” the brown eyes to blue eyes. If the melanin gene were to be completely turned off, humans would not have color anywhere (in their hair, or eyes or skin). This condition is called albinism. Therefore, there is limited genetic variation among the colors of people’s eyes because there is only so much melanin that can be turned on or off. Humans essentially have no carrying capacity because we are using our ability to manipulate technology and medicines to be able to sustain any number of people. This is interesting because this is the first time in the history of the earth that a species has been able to essentially escape the natural order and prolong lives when they are not meant to be prolonged. It may even be considered a bad thing that people are living so long. Evolution is always slowly occurring, but it has been occurring for hundreds of millions of years with other species and we have not been around long enough to see whether or not big changes have been made to our genetics. But, I will close my argument with this. People today are not only living longer than people 300 years ago, but we are also much taller and bigger than them. It may be a genetic mutation to have 6 foot tall people as opposed to the average 4 foot tall people that lived 300 years ago. So, yes, evolution is still occurring, but we have not been around long enough on an evolutionary scale to really see it happening.
ReplyDeletehttp://en.wikipedia.org/wiki/Cancer
http://www.sciencedaily.com/releases/2008/01/080130170343.htm
Evolution has not stopped, it has simply slowed down. As Michelle wrote, we humans simply find a way to “fix” our problems. Diseases, instead of selecting for individuals with genes that make them immune or help them fight off the disease more easily, are wiped out by vaccinations and modern medical treatments that eliminate this selective pressure. We have expanded the Earth’s carrying capacity for humans beyond normal means by eliminating limiting factors such as availability of building materials, water, food, temperature, space, and disease through new inventions. Building materials, water, and food are imported from areas that have a surplus. Temperatures are controlled with air conditioning units and heaters. Even space problems are dealt with by building up in apartment complexes and skyscrapers. Disease, as mentioned before, is controlled by vaccination and modern medicine. As if that weren’t enough, we don’t live “natural” lives in the sense that we don’t compete for resources on an individual level. Sitting in office buildings, we don’t find our own food and water sources, build our own homes, or even fight our own battles. Sexual selection is altered through cosmetic surgery and other factors such as inherited wealth. No competition, no selection. Those that are successful tend to have fewer children or none at all, marrying later in life and choosing to wait to have children in order to concentrate on careers.. In most societies, we are monogamous, but our self-imposed societal standards reduce our reproductive success, as those who are more successful at finding mates are restricted from producing offspring with partners other than the one they are married to.
ReplyDeleteHowever, there is still, however slight, some evolutionary pressure on humans to evolve. Diseases that we have no cure for, such as HIV, cancer, multiple sclerosis, and other diseases select for individuals who have a genetic resistance to the disease. A mutation in the CCR5 gene codes for HIV resistance in individuals with one copy of the gene and immunity in those with two copies. Since there is no sure for the fatal disease, those who have this gene, especially two copies of it, are naturally selected for as they increase the chances of survival and therefore reproductive success. As Jessica mentioned, many types of cancer have also been found to have an inherited genetic link and people with certain genes are more likely to get different types of cancer. Therefore, people without the cancer gene are more likely to reproduce and eliminate the cancer gene as those possessing the genes are more likely to die earlier and be unable to reproduce and pass on their defective gene.
http://en.wikipedia.org/wiki/CCR5