Change in Life over Time

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.


2


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


3


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


4


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.]


5


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.


6


Note that intentional probing questions throughout the lesson are key not only to formative

assessment, but to student’s confrontation of misconceptions.


7


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?


8


2. What, if any, change occurred between the first and second, and again between the


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


9


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,


10


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).

https://commons.wikimedia.org/wiki/File:Darwin%27s_finches_by_Gould.jpg


11


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.


12


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.


13


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.


14


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).

https://commons.wikimedia.org/wiki/File:Black_and_white_line_art_drawing_of_swainson_hawk_bird_in_flight.jpg

https://commons.wikimedia.org/wiki/File:Black_and_white_line_art_drawing_of_swainson_hawk_bird_in_flight.jpg


15


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


16


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


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


17


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?

http://www.gocomics.com/nonsequitur/2015/08/22

Documents

Change in Life over Time