EvolutionThe theory that species can change over time (more than one lifetime).

Natural Selection

How do species change over time?

GenerationThe entire group of organisms born around the same time.

OffspringA baby.

Trait A characteristic or feature that is passed down from parent to child.

VariationSlight differences in a population

What variation do you see in the snail shells below?

What variation do you see in the fish?

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What variations do you see in the puppies?

Color patterns in their fur

The length of their noses

How tall they are

The size of their ears

Maybe there are even variation in their behavior!

Advantageous Trait A characteristic that

helps an organism survive or reproduce.

It depends on the environment.

When only a few organisms have a trait that is helpful, it is called an advantageous trait.

The Environment is always changingIf the environment became extremely cold, which

of the puppies would be most likely to survive?

• If the environment became extremely hot, which of the puppies would be most likely to survive?

• If there was a food shortage, who would survive?

BrainstormWhat traits would be advantageous if you

live under water?

What traits would be advantageous if you live in the air like a bird?

AdaptationA useful characteristic that an entire population has.

When an entire population has a trait that is helpful, it is called an adaptation.

What population has advantageous traits for living under water?

What adaptations does that population have?

Essential question: Why do species change over time?

Species change over time because the environment is always changing.

When the environment changes & there is variation in a population, some organisms are able to survive better than others.

For example, during the ice age, animals with thick fur had the advantage. Only animals with thick fur survived and reproduced. The only giant dinosaur-sized creatures that survived in the ice age were wooly mammoths.

How does variation benefit populations?

Which snails would survive if the sand in the ocean turned red?

Which snails would survive if the sand in the ocean were yellow?

If the environment changes, a large population with lots of variation has a better chance of having some individuals survive and reproduce!

Why is variation in the snails beneficial?

Case Study #1: Giraffes

What traits do these giraffes have?What is the variation in this picture?Which giraffes are most likely to survive?Which giraffes are most likely to reproduce?What is the advantageous trait?How long will the necks of the next generation of

giraffes be?

Over Time what will the population look like if only the giraffes with long necks reproduce?

X

1. Define Adaptation.

2. Which of the following is an real adaptation?a) Zebras adapted black and white stripes to blend in better

with their environment.

b) After jumping into a cold swimming pool, your body adapts to the cold. The water starts to feel warmer.

THINGS YOU KNOW: In order to call a trait an adaptation, most or all of the

population must have that trait.Changes in evolution take longer than one lifetime to happen.

ANSWER: (Option A) After millions of years, all the zebra-like creatures without stripes died off and all the zebra-like creatures with stripes lived to reproduce.

A mechanism for change

Natural Selection

Three years ago, a group of squirrels’ environment changed.

A highway was built in the middle of the habitat and now the

squirrel population is divided! The forest to the left of the

highway stays the same after the highway is built. The forest on

the right side of the highway becomes a theme park. In the

theme park, the dark gray squirrels are especially visible to

the hawks that prey on them.

1. What has changed in the environment?

 

A Graph of the Fur Color of Squirrels in a Forest

There is variation in the fur color of a population of squirrels ranging from light gray

to dark gray. After a theme park is built, light gray squirrels are able to

camouflage on the concrete. Dark gray squirrels stick out like a sore thumb and

can be eaten by predators.

2. What is the variation in the squirrels?

3. Who is most likely to survive and reproduce?

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Natural Selection “Case Study F” 

A Graph of the Fish Size

On the east coast there are salmon in the ocean. These salmon are all

different sizes. When the British came to America in the 1800s more and

more people started hunting for salmon. These fishermen were paid by the

weight of fish rather than by the number of fish that they caught. The

fishermen thought of a plan to catch more large fish. These fishermen

started using nets with large holes so that they would catch only large fish.

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Natural SelectionWhich fish will survive, the large fish or the

small fish?Which fish will reproduce?How will the population of the fish change

overtime?

The Industrial Revolution in Europe

In 1760-1850, there was major change in Europe. People invented factories to make clothes and many other things, such as steel. The factories that people built, spewed out tons of soot and pollution. This black soot fell on the trees in Europe and turned the bark black.

A Case Study on Moths

Describe the Environment

Make observations about the tree barkWhat is the moth’s predator?

Birds put pressureon the moths

Describe the Population

Make observations about the moths.

What variation do you see in your moths?

The Industrial Revolution in Europe

1) Describe the variation in the population

2) Describe the Environmental Pressure (what changed?)

3) Determine the advantageous trait

4) Let several lifetimes pass; Organisms will reproduce

5) Determine what traits the next generation will have

6) Identify the change/adaptation

There are more dark colored moths than light colored moths because…

Dark colored moths can camouflage with the bark

Dark colored moths are more likely to survive because bird won’t eat them

Dark colored moths have the advantageous trait.

Dark colored moths reproduce and pass on their traits.

Almost all their offspring are Dark colored too.

adaptation

Identify the Change

If almost the entire population has the helpful trait, call it an ………………….

If only a few members of the population have the helpful trait, call it an……….

advantageous trait

Moths that were white were eaten by birds. Only black moths survived.

Moths needed to camouflage in order to survive, so they turned black.

Why are the moths able to change during the industrial revolution?

Natural Selection

Process that explains how species change over time.

Natural Selection is shorthand for saying: “Organisms who are best suited to the environment (who have advantageous traits) are more likely to survive and reproduce and pass on those traits to the next generation. Over time, the entire population changes. We say, the population adapts.”

Steps in Natural Selection

1) Describe the variation in the population

2) Describe the Environmental Pressure (change)

3) Determine the advantageous trait

4) Let several lifetimes pass; organisms will reproduce

5) Determine what traits the next generation will have

6) Identify the change/adaptation

Note: Natural Selection is sometimes called “survival of the fittest.”

•Fitness: The ability of an organism to survive to reproduce.

Mirror, mirror on the wall, who is the fittest of them all?

There is NO fittest species

It all depends on the environment.

Mirror, mirror on the wall, who is the fittest of them all?