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Biodiversity and Evolution
1
Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Lesson 2.4
Change in Life over Time To the Teacher The way to understand how different species evolved is to think about the niches that they fill in
an ecosystem - basically, how they make a living.
Steven Pinker
For roughly four billion years, life on Earth has changed, producing the amazing diversity of
flora and fauna seen today. In this lesson, students will gain an understanding of how species
evolve over time, driven by natural selection and dependent upon genetic variability.
To avoid the perpetuation of common misconceptions about evolution, the following table is
provided.
Common Misconceptions to Avoid When Teaching Evolution
Misconceptions Corrections
Organisms adapt to their
environment.
The term organism implies individual living things and
only groups of organisms can evolve; individual organisms
never evolve. Therefore, instead of utilizing the
ambiguous term, “organisms,” substitute “species” or
“populations.”
Organisms adapt within a
lifetime.
“Acclimations” that an individual organism might make
during its lifetime, consciously or otherwise, enabling it to
survive better (e.g. developing resistance to a disease or
adapting to higher altitude) are not adaptations.
Biological adaptations develop in a species or population
generally over a long period of time, involving many
generations.
In a similar sense, the word, “adaptation,” when used as a
verb for the process by which biological adaptations
develop usually refers to natural selection, a major
mechanism of evolution. To avoid confusion, instead of
saying organisms adapt, say a species or population
evolved the feature (or adaptation).
Evolution is purposeful. Environmental change drives evolution.
Biodiversity and Evolution
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Try to use phrases that reflect natural selection and avoid
using phrases that suggest that changes happen for some
ultimate purpose. In example, avoid phrases such as
“monkeys have long tails so they can move easily in trees”
or “birds have wings in order to fly.” Instead, say things
like “monkeys have tails because of changes over many
generations in a way that allowed the monkey to use its tail
as another appendage” or “birds have wings because long
ago, their arms changed over many generations in several
ways that enabled pre-birds to move from tree to tree faster
and more safely.”
In a similar sense, variation is random, but selection is not.
Objectives Students will be able to do the following:
1. Describe genetic variability and natural selection as mechanisms for evolution.
2. Explain the conditions required for natural selection that result in differential reproductive
success.
3. Refine their positions on the issue of the eradication of invasive species.
Time Needed Two 50-minute class period
Materials For alternative activity materials see Evolution & the Nature of Science Institute (ENSI):
o The Natural Selection of Stick-Worms at
http://www.indiana.edu/~ensiweb/lessons/ns.st.wm.html
o The Natural Selection of Bean Hunters at
http://www.indiana.edu/~ensiweb/lessons/ns.beans.html
Materials per class
o Computer with projector, sound, and internet access
Access to Pentatonix video clip, Evolution of Music at
https://www.youtube.com/watch?v=lExW80sXsHs
Access to Khan Academy video clip, Introduction to Evolution and Natural
Selection at https://www.khanacademy.org/science/biology/her/evolution-and-natural-
selection/v/introduction-to-evolution-and-natural-selection
o Optional class set of Khan Academy text, Darwin, Evolution, and Natural Selection
o Class set of Lesson 2.4 Science Notebook Template
Materials per group
Biodiversity and Evolution
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
o A copy of The Chips Are Down Lab sheet
o Large colorful floral or otherwise patterned fabric or paper piece (one uniform type for
the entire class may be preferred)
o Container with colorful paper chips (hole-punch construction paper), some of which
blend with the background fabric or paper.
100 chips is the easiest number to work with mathematically. Depending on your
fabrics and construction paper, you may start with 25 chips of 4 different colors, 20
of 5 different colors, or 10 of 10. For the entire lab, there should be 100 chips of
each color available to each group.
Materials per student
o Science notebook
Procedure
Advance Preparation
1. Prepare lab supplies.
2. Access video clip for projection.
Engage
1. Distribute the class set of Lesson 2.4 Science Notebook Templates for reference.
2. Explain to students that they are going to watch a video clip called the Evolution of Music
by the Pentatonix and then play the clip (4 min).
3. Ask the following questions.
What does the term evolution mean with regard to the video? [change over time]
What are some other things that change over time? [fashion, technology, ect.]
Why do these things change over time? [new tastes, innovations, etc.]
How does the meaning of evolution in these instances differ from the meaning of
evolution with regard to living things? [same, change over time]
Why do living things change over time? [environmental change; nature selects for the
best fit]
4. Prompt students to write their own definition of the term, evolution, in their Science
Notebooks.
5. Explain that as we proceed through our studies of evolution, what we are investigating is the
change in living things over time that are driven by changes in the environment.
Explore
1. Assign lab roles to group members. Rotate roles for investigations that follow.
Recorder-Reporter: records lab data and answers, reports for group, helps clean up
Materials Manager: gets materials, performs experiment, returns materials, helps clean
up
Director: reads directions to the group, asks the teacher for directions, leads the group
discussion, helps perform the experiment, helps clean up
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Time keeper: keeps time, checker (makes sure that all understand), helps with
experiment if needed, encouragers, helps clean up
2. Distribute a copy of The Chips Are Down Lab sheet to each group.
3. Read the introduction out loud, to set the stage for the lab activity.
4. Instruct students to carefully follow the directions to complete the lab activity and to record
all observations within their Science Notebooks.
5. Circulate, asking probing questions in to assist students in the confrontation of
misconceptions.
6. Facilitate a classroom discussion concerning the answers to the Discussion Questions,
randomly calling on students.
Was one color of paper chip represented more than others in the first generation of
survivors?
Were shades of that color similar colors also present?
What, if any, change occurred between the first and second, and again between the
second and third generation of survivors?
Compare the original and survivor populations. Is there any color form the original
population that is not represented in the survivor population? If so, what color or
colors?
Examine your survivor chips and the fabric from which you took them. How do you
think the colors of the survivors are related to their habitat?
Write a conclusion as to which colors survived in the habitat and which did not,
and why. Try to relate this to a natural situation.
Explain
1. Before viewing the Khan Academy video clip, Introduction to Evolution and Natural
Selection (17:38), instruct students to construct a KWL chart, recording what they know (K)
and what they wonder (W) about evolution and natural selection. See the Lesson 2.4
Science Notebook Template for reference.
2. Instruct students to record what they learn (L) about evolution and natural selection while
viewing the video.
3. Play the video (https://www.khanacademy.org/science/biology/her/evolution-and-natural-
selection/v/introduction-to-evolution-and-natural-selection).
4. Ask the following questions. Prior to randomly calling on students, allow for thinking,
writing, and collaboration time.
Is evolution the same as natural selection? Explain. [No. Natural selection is the
mechanism that drives evolution.]
In reference to evolution, what does the term adapt mean?
Do individual organisms or groups of organisms adapt? Explain [Groups of organisms;
nature selects for best-fit member of group, driving change of species or population over
time.]
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Can an organism or species choose to evolve? Explain. [No. Evolution through natural
selection is driven by environmental change.]
Would a population of organisms that is more or less genetically diverse be able to cope
with environmental change better? Explain. [Populations that are more genetically
diverse will cope better. Within a population of organisms that are genetically identical
or similar, an environmental change that wipes out one individual out will likely wipe
them all out.]
Organisms such as bacteria, dandelions, mosquitoes, and cockroaches reproduce
relatively quickly. Organisms such as elephants, sharks, orangutans, and humans
reproduce slowly. Which group of organisms will adapt to environmental change
quicker? Explain. [Organisms that reproduce quickly will adapt faster. Mutations will
arise faster, resulting in increased genetic variability of the population.]
Elaborate
1. Display the evolution cartoon. Prompt students to study the cartoon and then to write an
answer to the following question.
What are at least two reasons why the depiction of evolution is incorrect? Thoroughly
explain your reasoning.
Closure
Elaborate
Refine Vote: Students have explored evolution of Earth’s amazing biodiversity. With regard to
the unit question of the eradication of invasive species, there is much to contemplate. -Through
the eradication of invasive species, are we respecting or disrespecting nature with regard to the
billions of years spent in its selection of best-fit members?
Instruct students to readdress the unit question, “Should we eradicate invasive species?” and
allow time for students to adjust their previous votes by moving one of the sticky notes from
‘yes’ to ‘no’ or vice versa if so desired.
Make note of any shifts or trends in student voting. Ask the question, “Have you changed your
vote? Why or why not?” Randomly call on students to respond. Remind them that there are no
right or wrong answers, all comments will be respected, and open-mindedness will be practiced.
Assessment Evaluate
Students are monitored and assessed based on their participation in small group and class
discussions. Formative assessment is ongoing in order to continually reveal misconceptions and
to appropriately redirect instruction and questioning, so that the misconceptions are confronted in
a constructive manner.
Student accountability is additionally maintained through notebook checks.
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Note that intentional probing questions throughout the lesson are key not only to formative
assessment, but to student’s confrontation of misconceptions.
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
The Chips are Down Lab Introduction
Evolution depends on genetic variability and natural selection.
Genetic variability refers to variety in the genetic makeup of individuals of a population. Variety primarily results from mutations. A mutation is a permanent change in the DNA sequence within a gene. Mutations may arise during cell division or be the result of environmental factors.
Natural selection is the mechanism that drives evolution. When environmental conditions change, nature selects for individuals that are better adapted. This process is able to occur, because of genetic variability. As a result of this process, also known as “the survival of the fittest,” the genetic traits of a population change over time.
In this exercise, we want to reinforce the concept with a demonstration of how natural selection works. It is far too time-consuming to observe natural selection at work in natural populations, so we will use artificial populations consisting of paper chips.
Procedure 1. Spread out the fabric or paper habitat given to you by your teacher on the table top. 2. Count out ____ chips of each of the ____ colors for a total of 100 as your initial
population. 3. Appoint one person as the prey (chip) distributor. That person should spread the chips
out randomly over the entire fabric, making sure the chips do not stick together. The other members of the group should have their backs turned during this procedure.
4. The predators (other members) should turn around and take turns picking off the prey (chips) one by one until only 25 remain. COUNT CAREFULLY. Predators are to take the first chip they see and follow each chip to the discard area with their eyes so as not to see more chips, and keep track of the number of chips they get.
5. Carefully shake off the fabric to remove survivors (remaining 25 chips). 6. Group the survivors according to color. Count and record these numbers. 7. Assume each survivor produces three offspring. Using the reserve chips, place three
chips of the same color along with the survivors (i.e., take the number of survivors multiplied by 4).
8. Mix these chips together and re-distribute them randomly as in step 3. 9. Repeat the entire process two more times, making a total of three generations of prey
being preyed upon. Discussion Questions 1. Was one color of paper chip represented more than others in the first generation of
survivors?
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
2. What, if any, change occurred between the first and second, and again between the
second and third generation of survivors?
3. Compare the original and survivor populations. Is there any color form the original
population that is not represented in the survivor population? If so, what color or
colors?
4. Examine your survivor chips and the fabric from which you took them. How do you
think the colors of the survivors are related to their habitat?
5. Write a conclusion as to which colors survived in the habitat and which did not,
and why. Use the terms genetic variability and natural selection in your response.
Adapted from Evolution and the Nature of Science Institute (ENSI). The Chips Are Down. Retrieved from
http://www.indiana.edu/~ensiweb/lessons/ns.chips.html
Biodiversity and Evolution
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Darwin, Evolution, and Natural Selection Khan Academy
All Khan Academy content is available for free at www.khanacademy.org
View accompanying video at https://www.khanacademy.org/science/biology/her/evolution-and-
natural-selection/v/introduction-to-evolution-and-natural-selection
Key points
Charles Darwin was a British naturalist who proposed the theory of biological evolution by
natural selection.
Darwin defined evolution as "descent with modification," the idea that species change over
time, give rise to new species, and share a common ancestor.
The mechanism that Darwin proposed for evolution is natural selection. Because resources are
limited in nature, organisms with heritable traits that favor survival and reproduction will tend
to leave more offspring than their peers, causing the traits to increase in frequency over
generations.
Natural selection causes populations to become adapted, or increasingly well-suited, to their
environments over time. Natural selection depends on the environment and requires existing
heritable variation in a group.
What is evolution?
The basic idea of biological evolution is that populations and species of organisms change over time.
Today, when we think of evolution, we are likely to link this idea with one specific person: the
British naturalist Charles Darwin.
In the 1850s, Darwin wrote an influential and controversial book called On the Origin of Species. In
it, he proposed that species evolve (or, as he put it, undergo "descent with modification"), and that
all living things can trace their descent to a common ancestor. [What exactly is a species?]
Darwin also suggested a mechanism for evolution: natural selection, in which heritable traits that
help organisms survive and reproduce become more common in a population over time. [What
does "heritable" mean?]
In this article, we'll take a closer look at Darwin's ideas. We'll trace how they emerged from his
worldwide travels on the ship HMS Beagle, and we'll also walk through an example of how
evolution by natural selection can work.
Darwin and the voyage of the Beagle
Darwin's seminal book, On the Origin of Species, set forth his ideas about evolution and natural
selection. These ideas were largely based on direct observations from Darwin's travels around the
globe. From 1831 to 1836, he was part of a survey expedition carried out by the ship HMS Beagle,
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
which included stops in South America, Australia, and the southern tip of Africa. At each of the
expedition's stops, Darwin had the opportunity to study and catalog the local plants and animals.
Over the course of his travels, Darwin began to see intriguing patterns in the distribution and
features of organisms. We can see some of the most important patterns Darwin noticed in
distribution of organisms by looking at his observations of the Galápagos Islands off the coast of
Ecuador.
Darwin found that nearby islands in the Galápagos had
similar but non-identical species of finches
living on them. Moreover, he noted that
each finch species was well-suited for its
environment and role. For instance,
species that ate large seeds tended to
have large, tough beaks, while those that
ate insects had thin, sharp beaks. Finally,
he observed that the finches (and other
animals) found on the Galápagos Islands
were similar to species on the nearby
mainland of Ecuador, but different from
those found elsewhere in the world.
Darwin didn't figure all of this out on his
trip. In fact, he didn't even realize all the
finches were related but distinct species
until he showed his specimens to a skilled ornithologist (bird biologist) years later. Gradually,
however, he came up with an idea that could explain the pattern of related but different finches.
According to Darwin's idea, this pattern would make sense if the Galápagos Islands had long ago
been populated by birds from the neighboring mainland. On each island, the finches might have
gradually adapted to local conditions (over many generations and long periods of time). This
process could have led to the formation of one or more distinct species on each island.
If this idea was correct, though, why was it correct? What mechanism could explain how each finch
population had acquired adaptations, or features that made it well-suited to its immediate
environment? During his voyage, and in the years after, Darwin developed and refined a set of ideas
that could explain the patterns he had observed during his voyage. In his book, On the Origin of
Species, Darwin outlined his two key ideas: evolution and natural selection.
Image credit: "Darwin's finches," by John Gould
(public domain).
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Evolution
Darwin proposed that species can change over time, that new species come from pre-existing
species, and that all species share a common ancestor. In this model, each species has its own
unique set of heritable (genetic) differences from the common ancestor, which have accumulated
gradually over very long time periods. Repeated branching events, in which new species split off
from a common ancestor, produce a multi-level "tree" that links all living organisms.
Darwin referred to this process, in which groups of organisms change in their heritable traits over
generations, as “descent with modification." Today, we call it evolution. Darwin's sketch above
illustrates his idea, showing how one species can branch into two over time, and how this process
can repeat multiple times in the "family tree" of a group of related species.
Natural selection
Importantly, Darwin didn't just propose that organisms evolved. If that had been the beginning and
end of his theory, he wouldn't be in as many textbooks as he is today! Instead, Darwin also
proposed a mechanism for evolution: natural selection. This mechanism was elegant and logical,
and it explained how populations could evolve (undergo descent with modification) in such a way
that they became better suited to their environments over time.
Modern-day species appear at the top of the chart, while the ancestors from which they arose are shown
lower in the chart. Image credit: "Darwin's tree of life," by Charles Darwin. Photograph by A. Kouprianov,
public domain.
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Darwin's concept of natural selection was based on several key observations:
Traits are often heritable. In living organisms, many characteristics are inherited, or passed
from parent to offspring. (Darwin knew this was the case, even though he did not know that
traits were inherited via genes.)
More offspring are produced than can survive. Organisms are capable of producing more
offspring than their environments can support. Thus, there is competition for limited resources
in each generation.
Offspring vary in their heritable traits. The offspring in any generation will be slightly different
from one another in their traits (color, size, shape, etc.), and many of these features will be
heritable.
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Based on these simple observations, Darwin concluded the following:
In a population, some individuals will have inherited traits that help them survive and
reproduce (given the conditions of the environment, such as the predators and food sources
present). The individuals with the helpful traits will leave more offspring in the next generation
than their peers, since the traits make them more effective at surviving and reproducing.
Because the helpful traits are heritable, and because organisms with these traits leave more
offspring, the traits will tend to become more common (present in a larger fraction of the
population) in the next generation.
Over generations, the population will become adapted to its environment (as individuals with
traits helpful in that environment have consistently greater reproductive success than their
peers).
Darwin's model of evolution by natural selection allowed him to explain the patterns he had seen
during his travels. For instance, if the Galápagos finch species shared a common ancestor, it made
sense that they should broadly resemble one another (and mainland finches, who likely shared that
common ancestor). If groups of finches had been isolated on separate islands for many generations,
however, each group would have been exposed to a different environment in which different
heritable traits might have been favored, such as different sizes and shapes of beaks for using
different food sources. These factors could have led to the formation of distinct species on each
island.
Example: How natural selection can work
To make natural selection more concrete, let's consider a simplified, hypothetical example. In this
example, a group of mice with heritable variation in fur color (black vs. tan) has just moved into a
new area where the rocks are black. This environment features hawks, which like to eat mice and
can see the tan ones more easily than the black ones against the black rock.
Because the hawks can see and catch the tan mice more easily, a relatively large fraction of the tan
mice are eaten, while a much smaller fraction of the black mice are eaten. If we look at the ratio of
black mice to tan mice in the surviving ("not-eaten") group, it will be higher than in the starting
population.
Fur color is a heritable trait (one that can be passed from parent to child). So, the increased fraction
of black mice in the surviving group means an increased fraction of black baby mice in the next
generation. After several generations of selection, the population might be made up almost entirely
of black mice. This change in the heritable features of the population is an example of evolution.
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Karrie Wikman; University of South Florida; SCE6906; 17-05-27; revised 17-07-09
Key points about natural selection
When I was first learning about natural selection, I had some questions (and misconceptions!)
about how it worked. Here are explanations about some potentially confusing points, which may
help you get a better sense of how, when, and why natural selection takes place.
Natural selection depends on the environment
Natural selection doesn't favor traits that are somehow inherently superior. Instead, it favors traits
that are beneficial (that is, help an organism survive and reproduce more effectively than its peers)
in a specific environment. Traits that are helpful in one environment might actually be harmful in
another.
Natural selection acts on existing heritable variation
Natural selection needs some starting material, and that starting material is heritable variation. For
natural selection to act on a feature, there must already be variation (differences among
individuals) for that feature. Also, the differences have to be heritable, determined by the
organisms' genes.
Heritable variation comes from random mutations
The original source of the new gene variants that produce new heritable traits, such as fur colors, is
random mutation (changes in DNA sequence). Random mutations that are passed on to offspring
typically occur in the germline, or sperm and egg cell lineage, of organisms. Sexual reproduction
"mixes and matches" gene variants to make more variation.
Schematic based on similar schematic in Reece et al. Hawk outline traced from "Black and white line art
drawing of Swainson hawk bird in flight," by Kerris Paul (public domain).
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Natural selection and the evolution of species
Let's take a step back and consider how natural selection fits in with Darwin's broader vision of
evolution, one in which all living things share a common ancestor and are descended from that
ancestor in a huge, branching tree. What is happening at each of those branch points?
In the example of Darwin's finches, we saw that groups in a single population may become isolated
from one another by geographical barriers, such as ocean surrounding islands, or by other
mechanisms. Once isolated, the groups can no longer interbreed and are exposed to different
environments. In each environment, natural selection is likely to favor different traits (and other
evolutionary forces, such as random drift, may also operate separately on the groups). Over many
generations, differences in heritable traits can accumulate between the groups, to the extent that
they are considered separate species.
Based on various lines of evidence, scientists think that this type of process has repeated many,
many times during the history of life on Earth. Evolution by natural selection and other mechanisms
underlies the incredible diversity of present-day life forms, and the action of natural selection can
explain the fit between present-day organisms and their environments.
Darwin, evolution, & natural selection https://www.khanacademy.org/science/biology/her/evolution-and-natural-
selection/a/darwin-evolution-natural-selection
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Lesson 2.4 Science Notebook Template
Engage – The Pentatonix
1. What does the term, evolution, mean to you?
Explore – The Chips are Down Lab
Observations
1. Complete the data table.
Colors
Number at start-->
# after 1st predation-->
# after 1st reproduction-->
# after 2nd predation-->
# after 2nd reproduction-->
# after 3rd predation-->
Discussion Questions
2. Was one color of paper chip represented more than others in the first generation of
survivors?
3. What, if any, change occurred between the first and second, and again between the
second and third generation of survivors?
4. Compare the original and survivor populations. Is there any color form the original
population that is not represented in the survivor population? If so, what color or colors?
5. Examine your survivor chips and the fabric from which you took them. How do you think
the colors of the survivors are related to their habitat?
6. Write a conclusion as to which colors survived in the habitat and which did not, and why.
Use the terms genetic variability and natural selection in your response.
Explain – Khan Academy Introduction to Evolution and Natural Selection
Before and During the Video - KWL Chart
1. Before viewing the video, construct a KWL chart and record what you know and what you
wonder about evolution and natural selection. While viewing the video, record what you
learned about evolution and natural selection.
K – What I Know W – What I Wonder L – What I Learned
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After the Video – Discussion Questions
2. Is evolution the same as natural selection? Explain.
3. In reference to evolution, what does the term adapt mean?
4. Do individual organisms or groups of organisms adapt? Explain.
5. Can organisms or species choose to evolve? Explain.
6. Would a population of organisms that is more or less genetically diverse be able to cope
with environmental change better? Explain.
7. Organisms such as bacteria, dandelions, mosquitoes, and cockroaches reproduce relatively
quickly. Organisms such as elephants, sharks, orangutans, and humans reproduce slowly.
Which group of organisms will adapt to environmental change quicker? Explain.
Elaborate
1. Study the evolution cartoon and then describe at least two reasons why the depiction of
evolution is incorrect. Thoroughly explain your reasoning.
Credit: Wiley Miller, Non Sequitur (2015, Aug 22). Retrieved from
http://www.gocomics.com/nonsequitur/2015/08/22
Think about the answer to the following question and refine your vote on the issue: Do you
think that we are respecting or disrespecting the billions of years of nature selecting for its
best-fit members by eradicating invasive species?
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