understanding natural selection

The Theory of Evolution

(See Chapter 16 in your text)

Understanding Natural Selection

Evolution

Theory

What do these words mean?

What is a theory?Common English

languageA theory is...

A best guessA hypothesisSomething you

aren’t sure about

Science

A theory is...The result of many

experiments that all show the same thing

NOT a guessNo evidence has

been found against it

The processes that have transformed life on earth from it’s earliest forms to the vast diversity seen today.

A change in the genes!

MANY experiments and observations show the same conclusion

What is evolution?

Which genes had better evolutionary fitness?

Before the industrial revolutionAfter the industrial revolution

What happened to the population over time?

Which moths were the most common after the trees changed?

Why did the population change?

Could individual moths change color?

How would you observe this in the local environment?

Did a new species form?

What does a population need so it can evolve?

1. Inherited Variation

1. Inherited Variation2. Overproduction

What does a population need so it can evolve?

1. Inherited Variation2. Overproduction

3. Struggle to Survive

What does a population need so it can evolve?

1. Inherited Variation2. Overproduction

3. Struggle to Survive4. Successful Reproduction

What does a population need so it can evolve?

Thomas Malthus (late 1700s)

Is there enough food for all?

Years

Units of

FoodPopulationSize

Malthus said:At some point,

we will run out of food!

Charles Lyell – Principles of GeologyThe earth is very oldMany small changes over a long time can

produce big differences

How old is the Earth? How long does it take to change?

History of the theory of Natural Selection

How did the giraffe get its long neck?

(Early ideas about natural

selection)

History of the theory of Natural Selection

Jean-Baptiste de Lamarck (1809)

If an organism uses a body part it will get stronger

Then it can pass on that trait to its offspring

Acquired characteristics CAN’T be passed onYou can only pass on what is in your DNA

(which doesn’t change)

What do you think? Is that true?

Voyage of the Beagle (1831 – 1836)

Looked at specimens from all over the world

Saw similarities and differences and tried to explain them

Charles Darwin

Voyage of the HMS Beagle

What did Darwin see?Famous example of

finches in the Galapagos Islands

Each slightly different with different food sources

How did the finches get that way?Ancestor finch arrives on

an islandFinches spread to different

islands, each with a different type of food

Birds with beaks that eat the food best survive better and reproduce more

There are more birds with the right kind of beak on that island

Continues for many years...

But Darwin was not the only one!Another (younger)

scientist was studying the same thing

Alfred Russel Wallace came up with the theory of Natural Selection too

Sent a letter to Darwin asking advice

They published the idea together...

http://www.pbs.org/wgbh/nova/darwin/program-q-300.html

Why did Darwin wait more than 20 years to publish his ideas?

Darwin started thinking about Natural Selection in 1836

He published The Origin of Species in 1859

Why did he wait so long?

What do you think?