CH.1 – FINDING SPECIES SIMILARITIES

EH: 1.4.1 WARM-UPYou will use what you have learned about examining body structures in order to practice

identifying the shared body structures in two imaginary species. (7 min)

Shared structures are body structures that feature the

same parts (for example, bones) in the same pattern

and relative position in more than one organism.

EH: 1.4.1 WARM-UPThese are the bones of two imaginary species. Look at the body structures for

both species, then select which body structures these two species share.

EH: 1.4.1 WARM-UP

Which structure do these species not share?

Species A does not have a

back limb but Species B does.

This means that this structure

is not shared.

EH: 1.4.1 WARM-UP

Which structures are shared between Species A and Species B?

EH: 1.4.1 WARM-UP

If you look at the shared structures, there are still some differences. What are some of these?

Even though these structures look different, they are shared

because they both have some version of the structure. They both

have a skull, a backbone, a tail, and a front limb with the “one,

two, many” structure.

EH: 1.4.1 WARM-UPWhen we say shared structures, we are thinking

about kinds of structures (e.g., whether there

is a front limb) and their position relative to

other structures (e.g., the “one, two, many”

arrangement of the bones in the front limb),

but not about the size or exact shape of each

structure.

For example, even though the front limbs are

different sizes, they have the same bones in the

“one, two, many” arrangement, so this is a

shared structure.

Scientists look for shared structures to decide

if different species are related.

EH: 1.4.1 WARM-UPTake a moment to answer the poll question on page 2 in the warm-up.

If they aren’t yet sure what a common ancestor is, you can think about this question as

asking whether the two species might have any ancestors in common.

Do you think the two species from

the Warm-Up have any ancestors

in common?

EH: 1.4.1 WARM-UP

Project the results of the polls,

Explain why you think these

species do or don’t share a

common ancestor.

In the lessons to come, you will be learning more

about evolution, which is about studying those

changes through time to understand the history

of life on Earth. For now, you should focus on

what shared structures can tell us about the

relationships between species.

Some of you may have already

learned something about how

changes are passed on from one

organism to another while

studying subjects like

reproduction, how traits are

inherited, and natural selection.

EH – 1.4.2: SECOND READ – HOW YOU ARE LIKE A BLUE WHALE

Both of these terms will be useful today

as we reread a section of the article,

“How You Are Like a Blue Whale,” and

as we talk more about body structures

and how they can help us to tell

whether different species are related.

These terms should sound familiar to

you, since both were in the reading from

the previous lesson.

You will learn to read and interpret evolutionary trees and revisit the article for evidence about

why species share similarities. (18 min)

Vocabulary:

descendant species: a more recent species

that evolved from an ancestor population

common ancestor population: an older

population from which two or more newer

species descended

EH – 1.4.2: SECOND READ – HOW YOU ARE LIKE A BLUE WHALE

The purpose of rereading today.

As you reread, pay special attention to the shared structures

between species and how these can provide evidence about

common ancestors.

One important tool for examining these relationships is an

evolutionary tree.

The evolutionary tree can help provide the relationships between

descendant species and their possible common ancestors.

Paleontologists use tree diagrams like the small one that was in the

article, or the more complex one you explored in the Evolutionary

History Sim, in order to show relationships between organisms that

are alive today and those that are now extinct.

Today, we will spend more time investigating this kind of diagram;

we will examine the diagram in the article first.

EH – 1.4.2: SECOND READ – HOW YOU ARE LIKE A BLUE WHALE

Examine “How You Are Like a Blue Whale”

Reread the small excerpt below from the article “How You Are Like a Blue Whale” and answer the guiding questions.

As you read, think about this question: Why do different species share similar structures?

Humans and blue

whales have many

shared structures.

Based on this

information,

paleontologists

know that these

species

descended from a

common ancestor

population that

also had those

body structures.Answer Guiding Questions

When Finished analyzing this

excerpt.

EH – 1.4.2: SECOND READ – HOW YOU ARE LIKE A BLUE WHALE

Guiding questions we should consider while we

examine the evolutionary tree in the reading.

1. What are the descendants in this diagram?

2. What body structures did the common ancestor have?

3. What are the body structures that both descendants share

with this common ancestor?

4. Why do paleontologists make diagrams like this? What are

they trying to show?

whales, humans

backbones, radius and ulna, lungs, structures for milk.

backbones, radius and ulna, lungs, structures for milk.

To show evolutionary relationships between different

species that have a common ancestor.

EH – 1.4.2: SECOND READ – HOW YOU ARE LIKE A BLUE WHALE

They show that the whale and the human share a

common ancestor that had a backbone, radius and ulna,

lungs, and could produce milk. They show which

descendant species are descended from that same

ancestor population.

Trace back the lines from blue whales

and humans to the description of the

common ancestor population.

What do the lines show?What does the yellow arrow

show?

That descendants are all on

the right side of the diagram.

EH – 1.4.2: SECOND READ – HOW YOU ARE LIKE A BLUE WHALE

The important limitations of the

diagram.

As with all models, there are limitations to

what can be shown.

A diagram like this is a kind of model

that paleontologists use to organize the

way they think about living things.

EH – 1.4.2: SECOND READ – HOW YOU ARE LIKE A BLUE WHALE

The work you just did to understand the

diagram and how it shows relationships

between humans, whales, and their common

ancestors will help as you work again with a

more complex model represented in the Sim.

On an evolutionary tree, even though

individual animals are shown, these

animals represent entire species,

descended from entire ancestor

populations.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

You will trace back in time through an evolutionary tree, using shared structures to study

relationships between descendant species. (20 min)

Project The Great Tree of Life image and

discuss complexity of the tree in the

Sim.

Paleontologists use evolutionary trees to

make sense of the patterns of shared

structures among species.

Some of these visual representations are

simple, like the one in the reading, and

some are more complex, like the images in

the Sim.

Evolutionary trees can be even more

complex when they try to incorporate the

vast total of life on Earth.

This version of the tree

shows you how complex

a complete evolutionary

tree would be to look at.

Even this one is not

entirely complete.

Scientists often use

simplified models to

represent their ideas

because they are easier

to work with.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Open the Evolutionary History Sim in “Free Explore” Mode

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Let’s Project the Evolutionary History Sim and debrief the evolutionary tree in Tree View.

The Tree View opens to show all

life on Earth, but that you can

study some branches in more

detail.

You can navigate through the

evolutionary tree in Tree View by

selecting a section in the Tree

Navigation window or by

pressing the branch with the

same name in the main window.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

You can navigate through the evolutionary

tree in Tree View by selecting a section in

the Tree Navigation window or by pressing

the branch with the same name in the

main window.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Select the ANIMALS branch in Tree View

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Then press the lower of the two “i” icons.

In the reading, you saw a simple tree that showed that,

just as parents pass genes down to their children, an

ancestor population passes along certain body structures

to its descendants.

The “i” icon shows which structures a common ancestor

population passed on to descendant species.

Here you can see that early organisms passed on the

structure of muscles to all of the descendants that

branched off from this early common ancestor. This

common ancestor population lived millions of years ago.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

If you follow with your finger on the “i” icon,

we can see that snails, earthworms, Darwin’s

bark spiders, and sea stars all have the same

kind of muscles.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

If we trace the line to the

left from the orange “i” icon,

we can see that organisms

like sponges and jellyfish do

not have the kinds of

muscles that other animals

have.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Trace from the Muscles “i” icon along the tree to

Vertebrates at the bottom-right of the screen and

expand that branch of the tree.

At the bottom of the page, we can reveal more detail

about the Vertebrates branch of the tree.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

We can see that the vertebrate species also share the

structure of muscles because all vertebrates branch

off to the right of that “i” icon.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

You and a partner will examine a body structure from

the following list.

• vertebral column (Backbone)

• Jaws

• humerus/radius/ulna

• Neck

• limbs with digits (toes, for example)

You will be finding living species that share the body

structure that you are assigned.

This will help you answer the Investigation Question.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Sim activity instructions.

Read the Goals and Do portions of the instructions.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Sim activity instructions.

Read the Goals and Do portions of the instructions.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Sim activity instructions.

Answer the 2 questions at the bottom of the instructions

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Remember that you can trace along the tree, include expanding branches of the tree on the

bottom of the screen and that you can expand as many branches as you like.

Let’s discuss your

responses and

share what you

wrote.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Remember you have been

investigating why different

species can have shared

body structures.

From the article and the

Sim, you have learned how

shared structures provide

evidence that two species

descended from a common

ancestor that passed down

that structure to the

descendants.

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Today, we talked about how

species descend from a

common ancestor.

In your homework, you will go

back to the two living species

you compared during the

Warm-Up and look more

closely at their structures in

order to try to figure out

which of four fossil species

have the same body structures

that these species’ common

ancestor probably had.

Let’s take a moment to answer the poll question

again!

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

Project the results of the

poll, using the graph icon.

Have you changed your

answers? Why do you now

think these species do or don’t

share a common ancestor.

Let’s take a moment to answer the poll question

again!

EH – 1.4.3: TRACING STRUCTURES IN AN EVOLUTIONARY TREE

EH - 1.4.4 HOMEWORK

Students return to the two species they compared in the Warm-Up and attempt

to determine what their common ancestor might have looked like.