Notes – Natural SelectionChapter 5, Lesson 1

Charles Darwin

• Evolution is change over time.• The naturalist Charles Darwin was the first person

to write a thorough collection of evidence supporting evolution.

• Darwin’s theory serves as the basis of all biological research today.

Happy 203rd Birthday!!! 2/12/1809

Charles Darwin

• Darwin spent 5 years exploring South America and its remote islands, such as the Galapagos, on the HMS Beagle, starting in 1831.

Charles Darwin

• Darwin made observations about the diversity and uniqueness of organisms.– Many of the animals on the Galapagos were

similar, but not identical to animals in mainland South America.

– Darwin thought maybe the animals in the Galapagos originally came from South America and over time, they had evolved.

Charles Darwin

Mainland

South America

Galapagos Islands

Cormorants (sea birds)

can fly.

Cormorants are unable to

fly.

Iguanas have smaller claws for climbing.

Iguanas have larger claws to

grip rocks.

Charles Darwin

• Darwin found giant tortoises on all the Galapagos Islands, but nowhere else.

• He reasoned that each new population changed slightly, or evolved, to fit its unique environment on the island.

Charles Darwin

• Darwin was impressed by the diversity of finches from one island to the next on the Galapagos.

Charles Darwin

– All the same finches started on the islands.

– Darwin said that because they were separated on each island, future generations have to look and behave differently.

Charles Darwin

– The finches became different because they became suited to the different habitats on the islands.

Charles Darwin

Charles Darwin

• Selective breeding is ON-PURPOSE breeding of plants and animals to get offspring with desired characteristics.

• This does not lead to a new species - the organism can still breed with other members of its species.

Charles Darwin

Charles Darwin

Evolution has been directly observed by humans.

Over just a couple hundred years,

wolves evolved into a little Pekingese.

Just think what millions of years can do!!!

Darwin’s Theory of Natural Selection

• Evolutionary Biologists are like detectives.• They come on the scene AFTER the fact, but can

figure out what happened because of clues left behind.

Darwin’s Theory of Natural Selection

• Because of probability and genetics, some organisms have special traits that give them a survival advantage.

• If you survive longer, you produce more offspring.• Over many generations, those GOOD traits would

be common in the species.

Darwin’s Theory of Natural Selection

Darwin’s Theory of Natural Selection

Darwin’s Theory of Natural Selection• Sometimes changes

occur in genes and a new trait is created.

• If the trait is beneficial, the organism may survive and pass the trait on to the next generation.

• Genetic variation is necessary for evolution to occur.

Darwin’s Theory of Natural Selection

Darwin’s Theory of Natural Selection

• Although resources are limited, animals often produce more offspring than could survive.

• Darwin decided this was a natural process that selected which organism survived, and called it natural selection.

Darwin’s Theory of Natural Selection

Darwin’s Theory of Natural Selection

• Adaptation refers to traits that increase the likelihood of surviving and reproducing in a particular environment.

Darwin’s Theory of Natural Selection

• Four steps or requirements of Darwin’s theory of evolution by natural selection:– Step 1: Overproduction– Step 2: Variation– Step 3: Inherited variation– Step 4: Natural selection

Darwin’s Theory of Natural Selection

1. Overproduction – Organisms produce more offspring than can be supported by the available food, water, and shelter in an environment. Many will die due to natural events such as predation, competition, and starvation.

Darwin’s Theory of Natural Selection

2. Variation – Offspring vary in traits such as color and size.

(as shown in a hypothetical fish population below)

Darwin’s Theory of Natural Selection

3. Inherited Variation – This is only genetic variation, traits that are passed from parent to offspring. Sources of variation include mutations, formation of gametes, and sexual reproduction.

Darwin’s Theory of Natural Selection

4. Natural Selection – Individuals with inherited variations that are better to survive and reproduce in a particular environment will have more offspring, and thus pass on these favorable traits, than individuals without those features.

Darwin’s Theory of Natural Selection

What did Darwin observe about the tortoises and finches in the Galapagos?

A their large size

B their similarity to those on the mainland

C their adaptations to their environments

D their friendliness

5.1 Natural Selection

What is necessary for evolution to occur?

A selective breeding

B genetic variation

C populations isolated on islands

D none of the above

5.1 Natural Selection

What is not a main source of genetic variation?

A differences in diet

B sexual reproduction

C mutations

D gamete formation

5.1 Natural Selection

What is evolution?

A adaptations to particular environments

B genetic change in a population over time

C natural selection

D differences in traits

What is necessary for natural selection to occur?

A genetic variation

B constant environmental conditions

C isolate populations

D shortage of offspring

Which of the following is NOT one of the main sources of genetic variation in a population?

A mutations

B learned abilities

C formation of gametes

D sexual reproduction

What causes evolution?

A genetic variation

B environmental factors

C both

D neither

SCI 3.a

What is one reason exotic species can sometimes outcompete native species?

A they have no natural predators

B there are more of them

C the new environment is more favorable

D the natives are not adapted

SCI 3.e

Which of the following did not contribute to Darwin’s development of the theory of natural selection?

A overproduction of offspring

B competition with exotic species in the Galapagos

C an essay on human population growth

D similarities and differences of species in the Galapagos

SCI 3.b