Thursday, April 9, 2009
Humans Changing Selective Conditions
With the Industrial Revolution in England and North America, the coloration and lichen growth on trees where the peppered moth rests was altered. (Directly from page 52) There was a huge increase in the dark, melanic forms of the moth in these industrial areas and a decrease in the light form. After only 50 years, the frequency of dark form moths increased to 98% in some areas, but after the enactment of clear air laws, the percent of dark melanic moths quickly decreased. This is one example of how humans directly affect the process of natural selection of other species. What effect do humans have on their environment, and how does human involvment change the proccess of evolution and natural selection? Give a couple examples. Do humans have a positive or negative effect on the rest of the environment. Explain.
Subscribe to:
Post Comments (Atom)
We have caused many changes in our environment, but whether these effects are positive or negative is up for debate. One example of how we impact the environment is the construction of cities. Creating a city completely transforms what used to be a habitat for many animals. This is generally bad, since habitat destruction has caused many species to go extinct. When an organism goes extinct, its old niche will become unoccupied, upsetting the natural balance of an environment. However, constructing cities has also created new habitats for other species to thrive in. In Chicago, a prime example is the pigeon, which is a common site. Pigeons and other birds have taken advantage of the cityscape by building their nests high up on buildings. Thus, making cities hasn't really destroyed habitats, but just changed them instead.
ReplyDeleteChanging the environment forces animals to adapt or die. Birds have adapted very well to cities because they face very little predation pressure. With so little selective pressure, pigeons proliferate in cities and will probably evolve to take advantage of the new ecosystem. It's difficult to decide whether our presence is hurting/helping the environment. In a lot of cases, we're definitely hurting the environment, such as the destruction of coral reefs and rainforests. But are we not creating new ecosystems? If the animals adapt to the new ecosystems, the stress from the changing environment would be promoting evolution.
Altering the environment can have either positive or negative affects. In the case of human alterations to the environment, most changes have a negative affect on evolution and natural selection. For example, humans are cutting down the world’s rainforests at shocking rates. While this is happening, many species of rare organisms, many of which have not yet been discovered, are disappearing as the habitats of these organisms are being destroyed. When the planet loses entire species, or even large populations of a certain species, biodiversity is lost. With less variation in the gene pool, natural selection, and thus evolution, is hindered. Fewer organisms mean fewer mutations per generation and fewer positive mutations. This means it will take more generations to provide the same number of positive mutations after humans destroy parts of the rainforests.
ReplyDeleteAnother example of humans altering the environments is the introduction of a species into a “foreign” area. When a species is introduced into a new area, it throws off the fine balance of the ecosystem. The species could prey on a certain species that is an important source of food for another species. Another situation could occur where the introduced species becomes the prey, leading to an overpopulation of the species that would have been preyed upon had the new species not been introduced into the area. The fine balances of ecosystems should not be altered by humans. Like the example with the rainforests, the extinctions of certain species due to new predator-prey relations reduce the biodiversity of the world, which slows evolution and natural selection.
Humanities exploitation of natural resources has led to myriad detrimental effects on biodiversity. With humanities burgeoning population crossing the carrying capacities of the habitats it inhabits, mankind's attempt to sustain itself takes an immense toll on species used by man. With this in mind, if one considers the effect man has on the environment, then the effect is most definitely negative. "The abundance of species has declined by 40% between 1970 and 2000." (http://www.countdown2010.net/?id=41).
ReplyDeleteIn an isolated case take for example large fish in the human diet; 90% of all large oceanic fish species have disappeared in the last 50 years due to over-fishing (http://www.globalissues.org/article/171/loss-of-biodiversity-and-extinctions#MassiveExtinctionsFromHumanActivity).
Indeed mankind's attempts to conquer and exploit its environment have shaped the selection pressure on many species. Domestication serves as a great example of this. Take for example, the dogs, originally wolves. Selection pressures on wolves favored stronger, more ferocious and more effective predators. However, human's exploited dogs to help them with their hunts and to be faithful pets. Selective breeding by man applied artificial selection pressures on the wolves that favored more loyal and possibly smaller breeds.
Humanity’s effect on the climate, particularly climate change has altered many selection pressures on other organisms. For example in the case of coral reefs climate change has applied selection pressures on coral which favor more heat resistant coral. However, most coral species are unable to react to such selection pressures since warm waters force them to start bleaching, expel zooxanthelles, and subsequently starve. This process eliminates their ability to survive and thus reproduce. Similarly, anthropogenic climate warming will apply selection pressures that will endanger many plants species. For example, global warming would move the potential northern and southern population limits of Fagus grandifolia, American beech, (italics for all of the post) northward. To keep pace with this move the, American beech would have to move 7-9 km per year northward. This selection pressure favoring quick movement of the beech cannot be met because since the end of the last Ice Age, the beech has only moved 0.2 km a year. Thus the beech will most likely not be able to survive and reproduce due to human induced selection pressures. On the other hand, global warming has eased selection pressures on disease carrying vectors like mosquitoes. Warmer global temperatures have made originally cold areas more hospitable for mosquitoes, thus increasing the mosquito’s potential range. Essentially the selection pressures favoring cold-resistant mosquitoes have been weakened. The mosquito and species like the mosquito that will benefit from climate change are the minority however.
Human technologies such as cars or big factories are great for humans. However, they emit CO2 which has caused global warming. Global warming has created a change in climate for many different organisms. For example, the temperatures in Antarctica have increased. The higher temperatures cause the ice to melt. This changes the environment drastically for the animals that live there such as penguins and polar bears. The change in the environment causes a change in the pressures that exist on the animals. This therefore causes natural selection to favor the selection of different traits and mutations. Because the chance of mutations occur by chance over time, it is unlikely that the correct mutations will occur in short amount of time. The lack of time needed for change will cause many of the animal there to be extinct.
ReplyDeleteHumans are constantly changing the environment of other species for the better and the worse. When humans take advantage of resources and take advantage of the environment they realize there dangerous actions and try to fix them. For instance, humans are now trying to “go green” which includes simple actions such as carpooling to work. Humans do create changes, but they also have the brain power to try and fix them.
Although humans are creating new ecosystems when they cut down a forest and create a city, they are not allowing species time to adapt to the changes. Evolution occurs with natural selection by chance over time. If the changes were made slowly it would be possible for the specific changes to occur that would be beneficial in the new environments. However, cutting down an environment in a week is not a gradual change it is fast. Therefore, the change does not really promote evolution.
Human hunting has a large effect on population ecology. While it might seem that hunting would only make it more difficult for species to proliferate, some species are actually helped by hunting. Because hunters favor certain game, hunting societies and clubs carefully monitor what is killed every year to make sure that these populations stay plentiful. In some instances, hunters even hunt the predators of the preferred games species, thus relieving some pressure on the game species. Managers of hunting reservations also routinely kill or remove the weaker individuals in order to keep the active game population large and strong. As a result of all of these things, evolution is almost accelerated for gaming animals, much like it has been in other animals or plants humans have shaped for our own usage (ie. corn, cows, horses).
ReplyDeletePrevious comments have discussed pollutants making the environment more difficult to live in (see Becca's response), but none have addressed the effects of pollutants on the species' evolution itself. That is to say, none have considered the effects of carcinogens and other toxins on mutations in DNA. It is well known that certain chemicals, especially carcinogens, have effects at the molecular level and cause mutations in DNA. Additionally, increased amounts of ultraviolet radiation due to human depletion of the ozone layer will also increase mutation rates in organisms. Though we general see mutations from these sources as bad (the most common image conjured is that of cancer), these are just more ways in which mutations can occur - whether they are positive or negative mutations is entirely up to chance. Increased rates of mutation translates directly into increased rates of evolution. Additionally, having harsher environments increases the selective advantage provided by certain traits, increasing the ability of any given trait to become prolific (see Carroll p 48-52). Because of this, I think we should consider that although most of the environments man is creating are less hospitable towards life, these environments are also conducive towards increased rates of evolution.
Though it is definitely true that humans have a tendency to drastically change the environment they inhabit, I think that it is rather unfair to call this effect a good or a bad thing. If in the wild, one species naturally forces another species into limited territories or even into extinction, we don't consider this a "good" or a "bad" thing for that species to have done; it is merely survival of the fittest in action. Our effects shouldn't be scrutinized under a moral magnifying glass. That isn't to say, however, that we shouldn't consider our actions and the effects that they have on our neighbors on this earth. That would be contrary to our innate biophilia. I merely think that our actions should not be given the label of "good" or "bad".
Humans have enormous effects on their environment, and the many species that inhabit it. Humans are often responsible for altering the environment and the selective pressures of that environment. For example, deforestation alters the selective pressures of that forest. Rather than the specific environment selecting for traits and organisms adapted for living in areas of tree growth, such as the ability to swing from branch to branch, the environment now selects for traits and organisms adapted to life without trees. Humans affect the natural course of evolution and natural selection because of the fact that natural selection selects for the most advantageous traits for a certain environment. When that environment is changed, the traits that are best suited for the environment are changed, and therefore natural selection is altered. Humans can also change the natural course of evolution by selected breeding. Seen especially in livestock, such as cattle, as well as horses and dogs, humans breed animals by choosing a specific trait or multiple traits they want in the animals, finding organisms with those triats, and breeding only those organisms, so that all of the offspring will have those traits. This is used to produce "better" animals, better in the sense that they are more beneficial for human use.
ReplyDeleteIn terms of species, human involvement is in many ways neither positive nor negative, but rather quite neutral. By changing an environment, for example deforestation, it is true that we are harming some species that thrive in that environment by making a new environment that chooses for traits those species don't have. However, at the same time, by changing the environment, we are maing it more favorable to certain other species, those who thrive in the new environment. So, we are not having an overall negative effect, but rather a positive effect on some species and a negative effect on others.
As humans expand their niche to occupy most of the known world, they have significantly altered the environment and changed the course of evolution and natural selection. Genetic variation in the population that was advantageous to the environment is no longer viable due to changes in the environment caused by human encroachments. One predominate effect is the theory that humans have altered the climate. Green house gases released from the automobiles, factories, and power plant have dramatically increased the carbon dioxide levels in the atmosphere, which caused the Green House Effect and global warming. This increase in temperature has become very problematic for some species of trees. For example, the American beech needs to grow in a relatively cool environment. The current range of the beech is limited to the eastern United States. However, as the temperature increases, the beech must migrate north at a rate of 7-9 km per year to escape the heat. However, the current rate at which beech move at is only .2 km a year. The selection for this slow migration rate was favorable under the old climate patter. However, since the climate is increasing at a much faster rate than in the previous years, natural selection will be shifted towards individual beeches that have a fast migratory rate. Consequentially, in the future, fast migrating variations of beech will become dominate while slow migrating variations of beech will dwindle. Thus, beeches can be considered to have “evolved” from a slow migrating species to a fast migrating species.
ReplyDeleteI would have to disagree with Daniel’s assertion that humans have a neutral impact on the environment. Normally changes happen slowing and provides enough time for a population of species to accommodate to their environment. Although genetic variations are present in all populations, there is no guarantee that a variation favorable to new environment exist on hand. It can take thousands of years for this right variation to be born into the population. It will take even longer for this variation to become predominate. For example, Carroll state that for a light population of mice to produce black mice will take “less than 2000 years” and for this black mice to become dominate takes no less than “1 million years” (Carroll 63). However human activities such as deforestation and eutrophication of a lake occur under a year, a time period too short for any species to adapt. As a result, any small population of organism is easily drawn into an extinction vortex and the population continues to decrease until the species becomes extinct. Thus, humans have a negative effect on the environment.
The human population has grown exponentially, thus having a significant effect on the environment. Due to our use of fossil fuels, humans have induced changes in the natural recycling cycles in nature. Humans largely use coal to generate heat and electricity. However, the burning of the coal emits sulfur oxides and nitrogen oxides into the environment. The emissions ultimately convert into nitric and sulfuric acid when the oxides come in contact with the water in the atmosphere. The water in the air condenses and the acid is deposited onto the ground or into lakes through precipitation. Acid rain is any form of precipitation under the pH 5.2, which is the natural slightly acidic pH of “unpolluted” rain. Because the rain has a low pH, the rain greatly affects organisms that are osmoregulators. As we have learned, osmoregulators are animals that “control [their] internal osmolarity” (Campbell 939). In one instance, salt ion uptake is inhibited in low pH waters, so the fish in acidic areas cannot osmoregulate effectively. The affect of acid rain on fish relates to the biology theme of regulation, which deals with the regulation that maintains homeostasis. Because the fish cannot maintain a stable environment inside their body, which could affect the performance of enzymes that perform bodily functions, the fish die in areas with a high acidity. A fish in an acidic environment would experience the denaturing of its enzymes, and its death is further perpetuated by its inability to regulate its body with an uptake of salt ions. The acid rain would inhibit evolution because many of the fish in the acidic environment would die, thus reducing not only species biodiversity, but also the diversity of genes. As the population gets smaller, evolution would take longer, as the population can neither produce as many individuals with varied genes nor reproduce very quickly.
ReplyDeleteI would agree with Jia that human activity has greatly increased extinction. Because the environments that humans affect change more quickly than the organisms can adapt to the change, more and more species are going extinct. I cannot believe in Mr. Bersin’s view that human activity cannot be labeled because human activity is merely a result of the survival of the fittest. By causing mass extinctions, humans are altering the delicate balance of ecosystems. For example, we have learned that the dumping of garbage into lakes causes eutrophication, or the increase of chemicals in the water bodies. Eutrophication can cause the massive increase of phytoplankton or an algal bloom. Because of the algal bloom, the oxygen in the water becomes reduced, which kills the fish and the shellfish that need to utilize the oxygen. The lake experiences a snowball effect, as the decreasing number of shellfish reduce the number of its predators, and the reduced number of predators reduce the number of the predator’s predators. The decreased amount of fish will ultimately be harmful to humans, as humans will not be able to eat the fish for food. As the food quantity and quality decrease, humans themselves will suffer from hunger or malnutrition. Is it truly the survival of the fittest if the “fit” knowingly contribute to their own destruction?