Natural Selection

NATURAL SELECTION

WHAT IS A SPECIES?•A species is a group of organisms that can mate with one another to produce fertile offspring. A characteristic that helps an organism survive and reproduce in its environment is called an adaptation.

DO SPECIES CHANGE OVER TIME?

•Scientists observe that species have changed over time. The process in which populations gradually change over time is called evolution.

EVIDENCE OF CHANGE OVER TIME

•The remains or imprints of once-living organisms found in layers of rock called fossils.

•By studying fossils, scientists have made a timeline of life known as the fossil record. The fossil record organizes fossils by their estimated ages and physical similarities.

THINK/PAIR/SHARE Use the words adaptations, evolution,

and population in a sentence.

How do adaptations work?

Can you tell whether two organisms are the same species just by looking at them?

BELLRINGERUpright walking, hair, fingerprints, binocular vision, and speech are all traits that almost all humans have in common.

List the advantages and disadvantages of each trait.

Do you think the advantages are greater than the disadvantages? Why or why not?

Record your responses in your notebook.

OBJECTIVES• List four sources of Charles Darwin’s ideas about evolution.

• Describe the four parts of Darwin’s theory of evolution by natural that gradual processes had changed the Earth’s surface over selection.

• Relate genetics to evolution.

CHARLES DARWIN After Charles Darwin graduated from college, he

served as naturalist on a ship called the HMS Beagle. During a voyage around the world, Darwin collected thousands of plant and animal samples.

DARWIN’S FINCHES Darwin noticed that the finches of the Galápagos

Islands were a little different from the finches in Ecuador. And the finches on each island differed from the finches on the other islands

DARWIN’S THINKING• Ideas About Breeding The process in which humans select which plants or animals to reproduce based on certain desired traits is called selective breeding.

• Ideas About Population Only a limited number of individuals survive to reproduce. Thus, there is something special about the offspring of the survivors.

INFLUENCES ON DARWIN Thomas Malthus: wrote a book stating that

humans have the potential to reproduce rapidly, eventually overrunning the food supply

This led Darwin to realize that all species can reproduce rapidly, those who survive must pass on traits to their offspring to help them survive

Charles Lyell: Earth is old, allowed evolution to be a slow gradual process

DARWIN’S THEORY OF NATURAL SELECTION• What Is Natural Selection? Darwin proposed the theory that evolution happens through a process that he called natural selection. Individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals.

• Genetics and Evolution Today, scientists have found most of the evidence that Darwin lacked. They know that variation happens as a result of differences in genes.

BELLRINGERWrite the four parts of natural selection, and create a mnemonic device to remember each part by using the first letter of the words.

Write your response in your notebook.

OBJECTIVES• Give three examples of natural selection in action.

• Outline the process of speciation.

CHANGES IN POPULATIONS• Adaptation to Hunting People hunt elephants for their tusks. As a result, fewer of the elephants that have tusks survive to reproduce, and more of the tuskless elephants survive.

• Insecticide Resistance A few insects in a population may be naturally resistant to a chemical insecticide. These insects pass their resistance trait to their offspring, and an insect population gradually becomes resistant to the insecticide.

COMPETITION FOR MATES Many species have so much competition for

mates that interesting adaptations result. For example, the females of many bird species prefer to mate with males that have colorful feathers.

• Sometimes, drastic changes that can form a new species take place. The formation of a new species as a result of evolution is called speciation.

FORMING A NEW SPECIES• Separation Speciation often begins when a part of a population becomes separated from the rest.

• Adaptation Populations constantly undergo natural selection. After two groups have separated, natural selection may act on each group in different ways.

FORMING A NEW SPECIES Division Over many generations, two separated

groups of a population may become very different until the point when they can no longer mate with one another. At this point, the two groups are no longer the same species

Copyright © by Holt, Rinehart and Winston. All rights reserved.

ResourcesChapter menu

Passage 2 You know from experience that individuals in a population are not exactly the same. If you look around the room, you will see a lot of differences among your classmates. You may have even noticed that no two dogs or two cats are exactly the same. No two individuals have exactly the same adaptations. For example, one cat may be better at catching mice, and another is better at running away from dogs.

Continued on the next slide

Standardized Test PreparationChapter C5



Passage 2, continued Observations such as these form the basis of the theory of natural selection. Because adaptations help organisms survive to reproduce, the individuals that are better adapted to their environment are more likely to pass their traits to future generations.




1. In the passage, what does population mean?

A a school

B some cats and dogs

C a group of the same type of organism

D a group of individuals that are the same




1. In the passage, what does population mean?

A a school

B some cats and dogs

C a group of the same type of organism

D a group of individuals that are the same




2. In this passage, which of the following are given as examples of adaptations?

F differences among classmates

G differences among cats

H differences between cats and dogs

I differences among environments




2. In this passage, which of the following are given as examples of adaptations?

F differences among classmates

G differences among cats

H differences between cats and dogs

I differences among environments




3. Which of the following statements about the individuals in a population that survive to reproduce is true?

A They have the same adaptations.

B They are likely to pass on adaptations to the next generation.

C They form the basis of the theory of natural selection.

D They are always better hunters.




3. Which of the following statements about the individuals in a population that survive to reproduce is true?

A They have the same adaptations.

B They are likely to pass on adaptations to the next generation.

C They form the basis of the theory of natural selection.

D They are always better hunters.




Interpreting Graphics

The graph below shows average beak sizes of a group of finches on one island over several years. Use the graph to answer the questions that follow.




1. In which of the years studied was average beak size the largest?

A 1977

B 1980

C 1982

D 1984




1. In which of the years studied was average beak size the largest?

A 1977

B 1980

C 1982

D 1984




2. If beak size in this group of birds is linked to the amount of rainfall, what can you infer about the year 1976 on this island?

F The year 1976 was drier than 1977.

G The year 1976 was drier than 1980.

H The year 1976 was wetter than 1977.

I The year 1976 was wetter than 1984.




2. If beak size in this group of birds is linked to the amount of rainfall, what can you infer about the year 1976 on this island?

F The year 1976 was drier than 1977.

G The year 1976 was drier than 1980.

H The year 1976 was wetter than 1977.

I The year 1976 was wetter than 1984.




3. During which year(s) was rainfall probably the lowest on the island?

A 1978, 1980, and 1982

B 1977, 1980, 1982, and 1984

C 1982

D 1984




3. During which year(s) was rainfall probably the lowest on the island?

A 1978, 1980, and 1982

B 1977, 1980, 1982, and 1984

C 1982

D 1984




4. Which of the following statements best summarizes this data?

F Average beak size stayed about the same except during wet years.

G Average beak size decreased during dry years and increased during wet years.

H Average beak size increased during dry years and decreased during wet years.

I Average beak size changed randomly.




4. Which of the following statements best summarizes this data?

F Average beak size stayed about the same except during wet years.

G Average beak size decreased during dry years and increased during wet years.

H Average beak size increased during dry years and decreased during wet years.

I Average beak size changed randomly.




Math

Read each question, and choose the best answer.

Standardized Test Preparation

Average Beak Measurements of Birds of the Colores Islands

Island Ave. beak length (mm)

Ave. beak width (mm)

No. of unique species

Verde 9.7 6.5 5

Azul 8.9 8.7 15

Rosa 5.2 8.0 10

Chapter C5



1. What is the ratio of the number of species on Verde Island to the total number of species on all three of the Colores Islands?

A 1:2

B 1:5

C 1:6

D 5:15






Verde 9.7 6.5 5

Azul 8.9 8.7 15

Rosa 5.2 8.0 10

Chapter C5



1. What is the ratio of the number of species on Verde Island to the total number of species on all three of the Colores Islands?

A 1:2

B 1:5

C 1:6

D 5:15






Verde 9.7 6.5 5

Azul 8.9 8.7 15

Rosa 5.2 8.0 10

Chapter C5



2. What percentage of all bird species on the Colores Islands are on Rosa Island?

F approximately 15%

G approximately 30%

H approximately 50%

I approximately 80%


Island No. of unique species

Verde 5

Azul 15

Rosa 10

Chapter C5



2. What percentage of all bird species on the Colores Islands are on Rosa Island?

F approximately 15%

G approximately 30%

H approximately 50%

I approximately 80%


Island No. of unique species

Verde 5

Azul 15

Rosa 10

Chapter C5



3. On which of the islands is the ratio of average beak length to average beak width closest to 1:1?




Verde 9.7 6.5

Azul 8.9 8.7

Rosa 5.2 8.0

A Verde Island

B Azul Island

C Rosa Island

D There is not enough information to determine the answer.

Chapter C5



3. On which of the islands is the ratio of average beak length to average beak width closest to 1:1?




Verde 9.7 6.5

Azul 8.9 8.7

Rosa 5.2 8.0

A Verde Island

B Azul Island

C Rosa Island

D There is not enough information to determine the answer.

Chapter C5



4. On which island does the bird with the smallest beak length live?




Verde 9.7 6.5

Azul 8.9 8.7

Rosa 5.2 8.0

F Verde Island

G Azul Island

H Rosa Island

I There is not enough information to determine the answer.

Chapter C5



4. On which island does the bird with the smallest beak length live?




Verde 9.7 6.5

Azul 8.9 8.7

Rosa 5.2 8.0

F Verde Island

G Azul Island

H Rosa Island

I There is not enough information to determine the answer.

Chapter C5

Technology

Natural Selection