Chapter 10. Chapter 10: Evolution and Extinction
How do humans mimic the mechanisms of natural selection...
Interactive Study Guide
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Guiding Question 10.5
How do humans mimic the mechanisms of natural selection for their own purposes? What are some common misconceptions about evolution?
Why You Should Care
Humans have been genetically engineering organisms since prehistory using a process called artificial selection. By choosing which individual cow or variety of potato gets to reproduce from one season to the next, we are, in effect, putting selection pressure on those organisms and "weeding" undesirable traits out of the population. Traits that are undesirable for humans don’t necessarily make those organisms more fit to survive in nature, usually the opposite. There are many vegetable crops, such as carrots, fennel, and asparagus, for example, that have wild counterparts, but none of these wild vegetables are good to eat. Wild carrots (known as a wildflower called "Queen Anne’s Lace") have roots that are woody, pale, and not sweet. In nature, putting a lot of energy into making a big sweet root takes away resources that would be used for survival.
Artificial selection could take generations to produce domestic plants and animals as we know them today, but we have recently developed a way to speed it up by introducing foreign genes into organisms. There is a storm of debate and controversy surrounding the issue of genetically modified organisms. You should be informed enough to see through the "mad scientist" fears associated with this issue and decide what negative aspects of genetic engineering (many of them ecological) you should really be concerned about.
Question 10.1
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Question 10.2
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In artificial selection, humans determine what makes a species more fit for reproduction rather than natural competitive or sexual pressures. Therefore, the traits selected for don’t always make the species more fit for living in nature, usually the opposite.
Question 10.3
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Question 10.4
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Question 10.5
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Artificial selection happens when humans apply selection pressure on other species and cause them to accumulate different traits than they would accumulate from natural selection. Although grafting apple trees is an example of perpetuating traits favored by humans, it doesn't actually involve the trait being selectively bred repeatedly, so it's not actually artificial selection, just asexual reproduction.
Question 10.6
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Question 10.7
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Question 10.8
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Question 10.9
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Question
Short-Answer Questions
A friend has asked you to explain to him why he should believe in evolution or care about extinction. Briefly describe how you would use your knowledge of the history of extinction and the genetic basis of evolution to answer the following questions.
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1) Evolution is a process that involves species not individuals. For fish to evolve legs, there would have to be a genetically inheritable potential to develop genes that would eventually let goldfish grow legs. This would occur after many generations of goldfish if there were environmental pressures that made it advantageous to the survival and reproduction of the goldfish to grow limbs. This sort of accumulation of mutations and modifications could not happen within one fish.
2) Humans didn’t evolve from apes but from a common ancestor that we share with apes. Species change into different species as they accumulate mutations. Since there are multiple individuals and populations of most species, this means that one species may become many.
3) Evolution involves the selection for or against randomly arising traits based on various selection pressures. Since accumulated changes are random and selection pressures may vary, there is no goal to evolution. Humans aren’t the pinnacle of evolution, just one among millions of species.
4) Once traits arise and are selected for, both a removal of the selection pressure for that trait and a mutation to genetically "turn off" the trait must occur to get rid of it. Humans have not yet acquired the trait of not having an appendix, but since it does us no harm, usually, there is little selection pressure to favor any individual born without one. Evolution does not create perfect solutions.
5) Survival of the fittest is one of the reasons evolution occurs:
• Variations in traits exist because of mutations.
• Those traits are inheritable.
• Some traits will affect the chances an individual will survive long enough to reproduce.
• The most advantageous traits will accumulate in the species, and the species will change.
The last two points are survival of the fittest; all the points are evolution.
6) Although evolution does not have a goal, it does lead to species coevolving with other species in their ecosystems, making them important parts of those ecosystems.
7) You can observe shifts in the proportions of genes and traits in some species. In some cases, actual changes in species have been observed.
2) Humans didn’t evolve from apes but from a common ancestor that we share with apes. Species change into different species as they accumulate mutations. Since there are multiple individuals and populations of most species, this means that one species may become many.
3) Evolution involves the selection for or against randomly arising traits based on various selection pressures. Since accumulated changes are random and selection pressures may vary, there is no goal to evolution. Humans aren’t the pinnacle of evolution, just one among millions of species.
4) Once traits arise and are selected for, both a removal of the selection pressure for that trait and a mutation to genetically "turn off" the trait must occur to get rid of it. Humans have not yet acquired the trait of not having an appendix, but since it does us no harm, usually, there is little selection pressure to favor any individual born without one. Evolution does not create perfect solutions.
5) Survival of the fittest is one of the reasons evolution occurs:
• Variations in traits exist because of mutations.
• Those traits are inheritable.
• Some traits will affect the chances an individual will survive long enough to reproduce.
• The most advantageous traits will accumulate in the species, and the species will change.
The last two points are survival of the fittest; all the points are evolution.
6) Although evolution does not have a goal, it does lead to species coevolving with other species in their ecosystems, making them important parts of those ecosystems.
7) You can observe shifts in the proportions of genes and traits in some species. In some cases, actual changes in species have been observed.