The Struggle to Survive and the process of Natural Selection

You have 2 minutes to cut your notes in half, and glue them in on pages 58 and

59.

Darwin’s Theory of Natural Selection

•In order to understand natural selection, we must first talk about 2 things:

▫Genetic Variation

▫AND

▫The struggle to survive

Charles Darwin

Genetic Variation• What is it?

▫We know that traits are passed from mother and father to offspring (children), but not everyone looks the same.

▫Genetic variation is the fact that traits can vary amongst organisms. It is WHY everyone looks different!

Even plants!

Genetic Variation

•Some traits are better in an environment than others.

•If a trait is harmful, the organism might die.

•If the trait is beneficial, the organism is more likely to survive and reproduce.

Genetic Variation: Finches

However, survival depends on other factors…

The Struggle to Survive• The term “Struggle to

survive” was used by Thomas Malthus, a famous scholar, in an essay he wrote about the human population.

• He stated that if the population continued to grow unchecked, humans would eventually run out of food and space.

The struggle is

real

Population Growth•Darwin noticed that, like humans, animals

often produced more offspring than could survive.

•As population grows, more resources are needed…such as food, water, and habitat…

•Resources can’t always be provided to all individuals, so only selected individuals survive.

But how are the organisms selected?• Darwin set out to figure out

how the surviving organisms were selected.

• He reasoned that an organism that was better prepared to get food or protect it’s space would be better able to survive.

• Because of this, there is competition between organisms, and the animal better suited to the environment would ultimately “win” the competition.

Environmental Factors• Different habitats can also

put pressure on animals to survive as well.

• Organisms need to be prepared for living in a certain type of habitat in order to survive and reproduce.

• If they are suited to the habitat, they will pass the beneficial traits to their offspring.

This

This

VS.

Peppered Moth

Genetic Variation

Peppered Moth cont…

Before Industrialization After Industrialization

If there is a predator that eats peppered moths…

1. Which moth do you think was more common before industrialization?

2. Which moth do you think was more common after the lichen on the trees died?

So, what is Natural Selection?

•It’s a process!

Vocabulary - RIGHT

A process by which individuals with traits that better suit the environment are more likely to survive longer and reproduce more successfully.

• Inherited traits that increase an organism’s chance of surviving and reproducing successfully.

What are the key words in both definitions?

• Surviving and reproducing successfully.

Natural Selection

Adaptations

What does the text say?Pass out the textbooks and turn to page 216

1 - Overproduction 2 – Inherited variation

4 – Successful Reproduction

3 – Struggle to survive

Using the information from the text, draw and complete this organizer on page ______ in your notebook, in your own

words.

Recap

•What is natural selection?▫It is a PROCESS!▫Organisms overproduce,▫there is genetic variation▫there is a struggle to survive,▫You must live long enough to successfully

reproduce in order to pass on the traits▫It starts all over again…