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
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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
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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.
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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
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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?
2
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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
4
© 2013 ReadWorks®, Inc. All rights reserved.