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Artificial Selection: How Humans Can Sway Nature
Artificial Selection: How Humans Can Sway Nature
Susan E. Matthews
A few weeks ago, I was leaving a park in my neighborhood, and I walked past the dog park. There was quite a sight to behold: seven golden wiener dogs running around and playing. Now, just one of these dogs would have been fun to see, with its long funny body and golden curls. But all seven of them were a sight to behold. They almost looked like exact replicas of each other. The owner was also a big fan of his dogs—his T‐shirt had a cartoon picture of a wiener dog on the front. Next to him was a dog‐stroller of sorts. It was a big, wire cage with several different compartments layered on top of one another, each with little pillows and treats. These dogs travel in style—no walking on leashes for them. I was delighted when one of the dogs ran up to me and started sniffing my foot through the fence, and the dog owner was even nice enough to let me pet his brood for a few minutes. He told me the seven dogs I was looking at were really a big family—there was a mom, dad, four puppies and the dad’s brother, or the uncle. The puppies were almost a year old, so they were nearly full‐grown and the same size as their parents. These dogs looked so similar I was shocked the owner could tell them apart. The only © 2013 ReadWorks®, Inc. All rights reserved.
Artificial Selection: How Humans Can Sway Nature
one I could pick out was the uncle dog, who was a little darker and smaller than the other puppies. All of the dogs were very well behaved, too. I didn’t ask, but I had to guess that this man had intentionally bred the two larger, golden colored dogs together, so the results would be the lovable puppies I was in the process of adoring. In making this choice, this man was doing something that past breeders and farmers had been doing for years—he had selected the specific traits he liked, and made sure they were passed down to the next generation. This may also be part of the reason the dogs were so willing to let me touch and play with them—they had been specifically bred to have a pleasant temperament. Breeding has everything to do with genetics. Every living creature has genes, which is basically a code inside of the body that determines how you look and to an extent, act. Your genes determine how tall you grow, what color hair you have, and how quickly your skin gets sunburnt. Our genes are inherited from our parents, which is why you see family resemblance between parents, children and siblings. These genes are passed on through generations by either artificial or natural selection. Charles Darwin outlined the idea of natural selection in his 1859 book, On the Origin of Species, where he explained there are certain characteristics that help an animal survive, such as a sharp beak that allows birds in the Galapagos Islands to better find and eat their food. These sharp‐beaked birds survived long enough to reproduce, and their offspring had sharp beaks too. Eventually, all of this type of bird had the sharp beak. This sort of slow change through natural selection was the foundation of Darwin’s theory of evolution, the idea that all living creatures would evolve to carry the characteristics that allow them to be most successful. But even before Darwin outlined the ideas of natural selection, people were performing artificial selection themselves, without recognizing what they were doing. The difference between natural selection and artificial selection is simple: natural selection occurs in nature, and artificial selection is done by people. Artificial selection started when farmers realized they could improve their livestock and crops by only breeding together the very best of what they had. For example, if a cow produced more milk than another cow, and was generally more successful, the farmer would breed that cow with the fittest bull, in order to create the best possible offspring. With each new generation, the cattle would become even stronger and give © 2013 ReadWorks®, Inc. All rights reserved.
Artificial Selection: How Humans Can Sway Nature
more milk and meat, which helps the farmer. This is similar to natural selection, because the best traits are still continuing. But it is artificial selection because the farmer is intervening and speeding the up process. Humans have been doing this since as far back as the time of the Romans, over 2,000 years ago. Farmers have also bred plants using artificial selection in a way that is perhaps even more visible than animal breeding. One example is corncobs. Originally, the corn plant’s corncobs were very small and didn’t really provide a good food to eat. By continuously picking out the plants that had the biggest corncobs, the farmers continued to refine the plants. Today, a corn plant that offers the healthy, edible corncob is the most recognizable corn plant. Another example found in the wild is the mustard plant. Rather than just select for one trait, like the size of a corncob, farmers separated the plants out depending on their strengths. By doing this, they created a number of the plants we know and eat all the time today. For example, a farmer would separate out the mustard plants with large leaves, and only breed them with other mustard plants with large leaves. Over time, this ended up producing a very large‐leafed plant that today we know as cabbage. Other mustard plants were chosen for having very few flowers. As these mustard plants were continuously bred together, over time, they changed into what we now know as broccoli. Other vegetables that came from the artificial selection of the mustard plant include cauliflower, kale and Brussels sprouts. And the original mustard plant is still the source of mustard seeds, which we use to make mustard itself. Artificial selection is used in many ways beyond just expanding the number of vegetables we can pick between. It can make the wool we take from sheep softer, or improve the speed of racehorses. It follows all of the same principles as natural selection, but it tends to go even faster than natural selection already does. That’s because humans control it, and we do that after we observe what’s working in the species we’re breeding, and decide what it is we want in the next generation. © 2013 ReadWorks®, Inc. All rights reserved.
Questions: Artificial Selection: How Humans Can Sway Nature
Name:
Date:
1. According to the passage, what are genes?
A
B
C
D
a code inside
a code inside
a code inside
a code inside
way you act
the
the
the
the
body
body
body
body
of animals but not inside the body of humans
first discovered by Charles Darwin
that determines how you look and, in some ways, act
that doesn’t affect the way you look but does affect the
2. The author contrasts natural selection with artificial selection. How are they different?
A Natural selection favors the best traits, while artificial selection favors the worst
traits.
B Natural selection is done by people, while artificial selection occurs in nature.
C Artificial selection is a slower process than natural selection.
D Natural selection occurs in nature, while artificial selection is done by people.
3. Artificial selection has led to the creation of new vegetables. Which evidence from the
text supports this statement?
A Farmers used to separate out the mustard plants with large leaves.
B The original mustard plant is the source of mustard seeds, which we use to
make mustard itself.
C Mustard plants that had very few flowers were continuously bred together,
changing into broccoli.
D Corncobs used to be very small and didn’t really provide a good food to eat.
4. Based on the passage, what can be concluded about natural selection?
A Natural selection prevents evolution from taking place.
B Natural selection never takes more than a hundred and seventy-five years to
occur.
C Natural selection of traits occurs over the course of different generations.
D Human intervention is required for natural selection to work.
5. What is this passage mainly about?
A
B
C
D
artificial selection and how it compares to natural selection
the author’s encounter with wiener dogs at the neighborhood dog park
how certain plants have been produced through artificial selection
natural selection and Darwin’s theory of evolution
1
© 2013 ReadWorks®, Inc. All rights reserved.
Questions: Artificial Selection: How Humans Can Sway Nature
6. Why might the author have begun the passage with the story about the seven golden
wiener dogs?
A to prove that artificial selection is a new process that was invented recently
B to introduce the concept of artificial selection by engaging the reader with an
entertaining example
C to argue that only dogs can experience artificial selection
D to confuse the reader by including a personal story within a non-fiction text
about natural selection
7. Choose the answer that best completes the sentence below.
Artificial selection is similar to natural selection because the best traits are passed on,
__________ in artificial selection humans are intervening and speeding up the process.
A
B
C
D
so
since
because
but
8. Artificial selection started when farmers realized they could improve their livestock
and crops by breeding together what?
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______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
2
© 2013 ReadWorks®, Inc. All rights reserved.
Questions: Artificial Selection: How Humans Can Sway Nature
9. Explain what natural selection is by using the example of the sharp-beaked birds.
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
10. Why might humans prefer to select traits by artificial selection instead of simply
allowing natural selection to take place? Use information from the text to support your
answer.
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
3
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Teacher Guide & Answers: Artificial Selection: How Humans Can Sway Nature
Teacher Guide & Answers
Passage Reading Level: Lexile 1170
1. According to the passage, what are genes?
A
B
C
D
a code inside the body of animals but not inside the body of humans
a code inside the body first discovered by Charles Darwin
a code inside the body that determines how you look and, in some ways, act
a code inside the body that doesn’t affect the way you look but does affect the way you act
2. The author contrasts natural selection with artificial selection. How are they different?
A
B
C
D
Natural selection favors the best traits, while artificial selection favors the worst traits.
Natural selection is done by people, while artificial selection occurs in nature.
Artificial selection is a slower process than natural selection.
Natural selection occurs in nature, while artificial selection is done by people.
3. Artificial selection has led to the creation of new vegetables. Which evidence from the text supports this
statement?
A
B
Farmers used to separate out the mustard plants with large leaves.
The original mustard plant is the source of mustard seeds, which we use to make mustard
itself.
C Mustard plants that had very few flowers were continuously bred together, changing
into broccoli.
D Corncobs used to be very small and didn’t really provide a good food to eat.
4. Based on the passage, what can be concluded about natural selection?
A
B
C
D
Natural selection prevents evolution from taking place.
Natural selection never takes more than a hundred and seventy-five years to occur.
Natural selection of traits occurs over the course of different generations.
Human intervention is required for natural selection to work.
5. What is this passage mainly about?
A
B
C
D
artificial selection and how it compares to natural selection
the author’s encounter with wiener dogs at the neighborhood dog park
how certain plants have been produced through artificial selection
natural selection and Darwin’s theory of evolution
1
© 2013 ReadWorks®, Inc. All rights reserved.
Teacher Guide & Answers: Artificial Selection: How Humans Can Sway Nature
6. Why might the author have begun the passage with the story about the seven golden wiener dogs?
A
B
to prove that artificial selection is a new process that was invented recently
to introduce the concept of artificial selection by engaging the reader with an
entertaining example
C to argue that only dogs can experience artificial selection
D to confuse the reader by including a personal story within a non-fiction text about natural
selection
7. Choose the answer that best completes the sentence below.
Artificial selection is similar to natural selection because the best traits are passed on, __________ in
artificial selection humans are intervening and speeding up the process.
A
B
C
D
so
since
because
but
8. Artificial selection started when farmers realized they could improve their livestock and crops by
breeding together what?
Suggested answer: Artificial selection started when farmers realized they could improve their livestock
and crops by breeding together the very best of what they had.
9. Explain what natural selection is by using the example of the sharp-beaked birds.
Suggested answer: Students should explain that natural selection is the process by which certain
characteristics that allow animals to be successful in their environments are passed on across generations.
Sharp beaks help birds find and eat their food. These sharp-beaked birds survived long enough to
reproduce, and their offspring had sharp beaks too. Eventually, more of this bird species had the sharp
beak. Thus, this slow change through natural selection favored the trait that helped these birds survive in
the Galapagos Islands.
10. Why might humans prefer to select traits by artificial selection instead of simply allowing natural
selection to take place? Use information from the text to support your answer.
Suggested answer: Answers may vary, but students should explain that artificial selection allows
humans to choose the traits of a plant or animal they want preserved in the plant or animal’s offspring.
For example, a farmer is able to breed the cow that produced the most milk with the fittest bull in order to
create offspring that would either produce a lot of milk or be very strong bulls.
Students may also explain that humans might intervene in order to speed up the process of selecting the
best traits in a species. Such was the case with farmers who bred the biggest corncobs to refine the corn
plant. Instead of waiting on nature, the farmer was able to breed the plants for the plant type that would
provide him with the most value in the quickest manner.
2
© 2013 ReadWorks®, Inc. All rights reserved.