Monday, April 13, 2009
Unnatural Selection
On page 234, Carroll discusses how hunters desire for large-horned rams has caused an "unnatural selection". Briefly summarize what "unnatural selection" means and provide other examples of other species of animals that humans have impacted in a similar manner. What are some of the effects of human pressure on these species? How has human intervention resulted in disadvantages for the vitality of the species? Are there any other possible benefits to forced human selection beside the monetary rewards for humans?
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Unnatural selection is human caused, forced selection that counters what would normally occur in an environment. Carroll uses the example of the hunting of bighorn sheep in Wyoming and surrounding ranges and how it has influenced the “breeding value” of the species. Because hunters desire rams with longest horns, they rid the area potential mates for females that also desire larger male bighorn sheep. Human selection in this situation drives evolution in the opposite direction for what is best for the natural population.
ReplyDeleteCod and other fishing populations have been negatively effected by overfishing. Fisherman select the largest and most mature fish because they sell for the most money, however, this results in a very young, immature population that is very vulnerable to predation. Because the population becomes more vulnerable to predators, the population cannot successfully recover from the fishing.
Human intervention in ecosystems has disrupted the natural balance maintained by food chains and food webs in that region. When humans target a certain species, whether for safety reasons or monetary gain, other species that prey on that species suffer. Also, species that the hunted species feeds on will drastically increase in population, and this can have very adverse effects on an ecosystem.
Chris Darimont, a postdoctoral fellow at University of California Santa Cruz, analyzed 40 “human predator systems” and found that in 95% of cases, hunting by humans accounted for decreases in horn size/ body size. In 97% of cases, hunting was also responsible for animals reproducing at earlier ages, leading to more defects and increasing vulnerability to predation. In virtually all of the studied scenarios, hunting by humans outpaced nature-driven trait changes by over 300 percent.
Unnatural selection facilitated by humans only has very few positive effects on certain members of a population, and these effects are temporary. Hunting a certain species allows its prey to flourish, however, in time, the disruption of the food chain will come back to harm that species anyway.
http://dsc.discovery.com/news/2009/01/13/hunting-animal-size.html
The peppered moth, Biston betularia, is an example of a species that humans impacted its natural selection. The Industrial Revolution, caused by humans in areas of England and North America, resulted in the rapid increase in the frequency of dark, melanic forms of the moth in industrial areas and a dramatic decrease in the light form. From 1848 to 1896, the dark form increased and evolved to as high as a 98% frequency in some areas. The selection coefficient against light forms of the peppered moth was on the order of negative 0.2. However, after clean air laws were enacted, the selection pressure reversed and the dark melanic form of the peppered moth decreased from above 90% of peppered moths to less than 10% in some locations. Since the industrial revolution caused trees and the peppered moths’ environment darker with industrial wastes, the light forms of the peppered moths were more prone to death due to predators, birds. Birds are able to spot the light peppered moths better than the dark peppered moths, resulting in the rapid decline in the light peppered moth population. After clean air laws were enacted, the tress and the environment of peppered moths also lightened up, resulting in the selective advantage of light peppered moths, allowing a camouflage with the trees. The dark peppered moths, in this case, became a selective disadvantage, resulting in less dark peppered moths from the lighter environment. This is a form of unnatural selection, since the acts of humans caused the selection of certain moths. The industrial waste products expelled into the air and into the environment due to humans’ inventions and progression in industries caused the selective advantage of dark peppered moths and the decrease in light peppered moths. If humans did not exist and no industrial revolutions were formed, then the light peppered moths would have had a better survival rate due to the lighter environment. The human intervention caused the disadvantages of light peppered moths’ body color compared to its environment, making it easier for them to become the prey of other birds.
ReplyDeleteA benefit to forced human selection may be the advantage to another species other than the species becoming unnaturally selected against. The dark melanic peppered moths, in this example, are given an advantage in their environment due to their body color, resulting in a higher survival rate than usual. However, I believe that the selection of species due to humans’ interactions and intervention is part of natural selection. Humans evolved in a way that allowed their brains to function in a highly sophisticated manner, developing many technologies for the survival and the improvement of the life of humans. The various effects caused by humans are a result of the humans’ intelligent mind caused by natural selection, and therefore the acts by humans that impact other species to have selective disadvantages or advantages are part of the natural world, and ,therefore, it should be natural selection, not unnatural selection.
http://en.wikipedia.org/wiki/Peppered_moth
As Ryan and Amie said, unnatural selection is human caused, forced selection that counters natural selection. In addition to their examples, I would like to add few more details.
ReplyDeleteFirst, I would like to talk about Amazon Rain Forest. Amazon rain forest is perhaps the world’s greatest remaining natural resource. Amazon rain forest contains largest collection of plant and animal species. However, a lot of scientists estimate that Amazon rain forest could be consumed in less than 40 years due to paper industry, logging, and grazing land. How disappointing would it be if we lost all of our precious animals and plants? Rare animals such as jaguars, pink dolphins, and golden lion tamarins are endangered by this unnatural selection. No matter how well these animals are fit in this environment, they can not survive because of incessant human activities that keep changing their environment way too fast.
Now there is different kind of unnatural selection. I remember back in Ap bio class when Mr. Erdman was saying that apple has great selective advantage because of its taste. If humans didn’t love apples, apple trees wouldn’t be as successful as today. Humans are protecting the apple tree from the natural selection and as long as humans are alive, apples will definitely survive. Basically, apples are benefiting from human intervention.
In addition, even though that unnatural selection is caused by humans, I want to say that it is part of natural selection. Since humans are the ultimate predators, if animals don’t evolve to escape from humans, I wouldn’t say that they are naturally fit. In some way, unnatural selection is part of natural selection because humans are part of the environment.
http://en.wikipedia.org/wiki/Golden_Lion_Tamarin
http://www.rain-tree.com/facts.htm
Unnatural selection is is evolution in the opposite direction. This means that what used to be a selective advantage and a trait that the species preferred, has become one that has harmed the species as a result so the species start to evolve without this trait. Since both hunters and female bighorns both desire rams with larger horns, there have been some “critical unintended consequences of the selective hunting” (254). The unintended consequence that Carroll is talking about is evolution in the opposite direction. What this means is because of hunting, rams have started to select against the faster growing horns and started to favor shorter horns. This is very strange because they are starting to evolve in the opposite direction away from their naturally selected optima that the females prefer.
ReplyDeleteThis is also seen in elephants. Since tusk less elephants are not as favorable by hunters, their population has increased from 2% to 38%.Due to hunting and fishing, the consequence is that large and rapid changes occur in certain characteristics in order for the species to survive. This is natural selection working in the opposite way. What seemed to be the best trait and the trait with the most benefits, has turned deadly and in return is killing species with those traits.
The average size of many species has gone down as a result to hunting and unnatural selection and because the prized parts of the species' gene pools are simply no longer there. There are other scientists besides Carroll who have studied the decline in size of the rams horns. Biologist Marco Festa-Bianchet of the University of Sherbrooke in Quebec found a 25 percent decline in the size of horns on bighorn sheep over the past 30 years. Since it is around the age of 4 that their horn size makes them legal game and that is several years before their reproductive peak, smaller-horned males get far more opportunities to mate. And since the big horned males are usually killed before they can reproduce, the smaller rams mate and therefore create more small horned rams.
http://www.nature.com/nature/journal/v457/n7231/full/457803a.html
http://www.fieldandstream.com/blogs/fshuntress/2009/01/unnatural-selection-2
Unnatural selection is selection in the direction opposite the one nature intended. It is human caused and has no benefit to the species being selected. The best way to explain this is to give an example. The example Carroll gives is the example of the bighorn rams in Wyoming. These rams are hunted for their namesake, that is, their horns. Hunters do not waste time hunting the rams with small horns. Only the large horns can be sold for enough money. As a result, the larger horns, which would usually be a selective advantage, are now a disadvantage. They make the animal more likely to be killed by a hunter and less likely to survive and reproduce.
ReplyDeleteA similar situation can be seen among the Red Kangaroos of Australia. The larger animals are more likely to be killed for their leather. In nature, bigger body size is better. It provides for better defense, and the ability to run faster from predators or towards prey. This is clearly a selective advantage. However, when being larger means that the animal is more likely to be killed this suddenly becomes a selective disadvantage. Such is the nature of unnatural selection: traits that would have been selected for by nature are now disadvantages.
The examples do not end here. The African Elephant is often hunted for its tusks. These tusks provide the animal better defense and are therefore a selective advantage in nature. However, they have recently become a disadvantage because of the increased likelihood of hunting if the animal has large tusks. Because they are not able to be used for ivory, tuskless elephants have become much more common in recent years. Prior to the explosion of elephant hunting, only 2% of African Elephants were tuskless. In a population of African Elephants in Zambia, this figure has risen to 38%. In South Africa, the increase was about as dramatic as possible. Recently, a population of African Elephants in South Africa was found to be 98% tuskless.
It can be seen that although these animals may seem to be less fit for their environment due to human intervention, this is not the case. In areas where hunting is prevalent, it has become a selective advantage for these animals to be small, small-horned, or tuskless. Human predators now play a major role in the evolution of these species. They are a part of their environment. By losing adaptations that have made these animals more likely to survive and reproduce in the past, they are more likely to survive and reproduce in their current environment. If humans stopped hunting these animals permanently, the traits such as big horns, large body size, and tusks would reemerge. Selection has the power to make species adaptable to whatever situation is thrown at them: natural or unnatural.
http://www.newsweek.com/id/177709?from=rss
Carroll 254-256
I am going to take a look at this question from both angles- that unnatural selection does not necessarily hurt a species; it might actually help it. Also, since all the previous posters already went into the details of specific examples (the peppered moth, cod, African elephant, and bighorn), this response is going to be more general. However, in addition to looking at human intervention from different points of view, I am still going to give specific examples of unnatural selection, just so I can answer the question.
ReplyDeleteSo how can human intervention help a species instead of harm it? Humans have been destroying habitats ever since cities started being built. Creating a city means destroying an environment, causing many species to go extinct. However, the construction of cities has created new and safe habitats for some species, such as the pigeon. Anybody who takes a quick walk around Chicago will notice the abundance of pigeons. This is because pigeons, and birds in general, thrive in cities. These “city pigeons” are called feral pigeons. They face little predation and relatively little competition for food (given the size of cities compared to the population of birds that live in them). Also, birds get to build their nests high up on buildings, instead of on nature-restricted trees, which can only grow so high. So yes, human intervention has destroyed habitats and caused animals to go against the natural selection current, but it has also helped out some species as well.
One negative aspect of human-induced selection not mentioned by the previous posters is “introduced species”. When a species is introduced into a new area, it throws off the balance of the ecosystem there. An example of this would be the African Honeybee. The African honeybee was brought to Brazil in 1956, but escaped to the Americas. They are extremely aggressive, and drove out established colonies of Italian honeybees. It has also caused human casualties. It has had a profound impact on the honeybee industry due to its aggressive nature; it has driven out virtually all its competitors, and is spreading rapidly. This is all due to human intervention; if humans had not brought the African honeybee to Brazil (for breeding purposes), none of this would have happened.
I am now going to give a specific example of unnatural selection caused by humans. This one has not been mentioned yet: dogs (originally wolves). Originally, selection pressures favored stronger, more ferocious wolves. Stronger wolves make better predators. However, humans have exploited dogs, and have taught them to be obedient, submissive, and loyal. Selective breeding by humans has caused artificial selection on wolves that went against the current of natural selection. Humans have caused ferocious dogs with ears pointed up (for intimidation) to turn into loyal, smaller, and submissive dogs (with ears down typically, except for “guard dogs” such as the german shepherd).
Another example is coral reefs. Humans have caused global warming due to carbon dioxide emissions. Because of the increased temperature over the years, selection has favored more heat resistant coral. However, most coral species are unable to react to these selection pressures because warm waters force them to starve. They starve because they start bleaching and expelling zooxanthelles. This process eliminates their ability to survive and reproduce (not a selective advantage). With this dilemma, corals have nowhere to go; they are at a disadvantage no matter which direction they go.
Humans will always affect the environment they live in. We can only hope that future generations try to limit the negative effects of human intervention.
http://en.wikipedia.org/wiki/Coral_reef
http://en.wikipedia.org/wiki/Wolf
Campbell Biology Edition 6
http://en.wikipedia.org/wiki/Feral_Pigeon
Monday, April 13, 2009
ReplyDeleteUnnatural Selection
On page 234, Carroll discusses how hunters desire for large-horned rams has caused an "unnatural selection". Briefly summarize what "unnatural selection" means and provide other examples of other species of animals that humans have impacted in a similar manner. What are some of the effects of human pressure on these species? How has human intervention resulted in disadvantages for the vitality of the species? Are there any other possible benefits to forced human selection beside the monetary rewards for humans?
Answer:
Unnatural selection is caused by humans and counters natural selection. It is forced selection in the opposite direction. Humans choose what they want for their own benefits rather than for what are best for that species or ecosystem. Humans have long considered themselves the true kings of the animal kingdom, and therefore practice dominion over every other organism out there. This forced selection can be very damaging for populations because instead of evolving beneficial traits like they could have without human interference, the human population is causing a different direction in evolution or sometimes even backwards evolution for their own benefit. Humans have always striven to enhance human capabilities and extend lifespan. With ever-advancing scientific understanding and technological capabilities, humanity stands on the brink of the potential next stage of evolution: evolution engineered by us. Nanotechnology, biotechnology, information technology and cognitive science offer the “possibility to enhance human performance, lengthen life-span and reshape our inherited physical, cognitive and emotional identities” (“The Challenges of Engineering Tomorrow’s People”). Our use of technology is interfering with nature and the process of evolution.
Fishing and hunting by humans are the main causes of mortality in many populations of wild animals. The consequence is that large and rapid changes occur in certain characteristics that far exceed changes due to other agents. Harvesting by humans exerts tremendous pressure on wild populations, resulting in both ecological and evolutionary change. Fishing negatively affects the evolution in lakes and other marine habitats because fishermen pick the biggest fish, killing them and then selling them. The fish left are slightly smaller because the big fish have been taken. Now the fish species in general are becoming smaller sized because of the effect the human fishermen had. This smaller size might not be beneficial for the series and then cause extinction. Also, food chains will be disrupted and the predators of the fish may be led to endangerment or extinction as well.
We can now genetically engineer and modify different organisms such as plants and “grapples”. In a sense we are making our own evolution with out thinking about the ramifications that come with this new responsibility. Our technology has given us the power to interfere with natural selection but the problem is abusing that power.
http://www.nature.com/nature/journal/v457/n7231/full/457803a.html
http://www.earthscan.co.uk/?tabid=34092
http://www.sciforums.com/showthread.php?t=2625