chapter 16 evolutionary theory section 1 … · his ideas about evolution? evolution is the process...

As you read this section, keep these questions in mind:

• Why is evolutionary theory associated with Charles Darwin?

• How was Darwin influenced by his personal experiences?

• How was Darwin influenced by the ideas of others?

KEY IDEAS

How Did Darwin’s Experiences Influence His Ideas About Evolution?Evolution is the process by which species change

over time. Modern evolutionary theory began when

Charles Darwin presented evidence that evolution

happens and gave an explanation of how it happens.

THE VOYAGE OF THE BEAGLE

In the 1830s, Darwin took a global voyage on a

ship called the Beagle. This voyage inspired many of

his ideas. During the voyage, Darwin collected many

natural objects, including nine species of finches in the

Galápagos Islands. The birds were very similar, but their

beaks differed in size and shape. He also noted that many

of the islands’ plant and animal species were similar to

species in South America.

Each finch has a beak that is suited to the food it eats.

Darwin proposed that the finch species descended

from a single South American species. The descendants

became modified, or changed, over time to survive on dif-

ferent foods. Darwin called such a change descent with

modification. This idea was a key part of his theory.

After he returned from his voyage, Darwin studied his

data for years. He did not report his ideas about evolution

right away. Instead, he took time to gather more data and

to form a good explanation for how evolution happens.

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

Interactive Reader 165 Evolutionary Theory

Name Class Date

READING TOOLBOX

Underline As you read, underline the descriptions of experiences and ideas that influenced Darwin.

BackgroundRecall that in science, a theory is a broad explanation that has been scientifically tested and supported repeatedly.

Hypothesize How do you think the foods eaten by the small-beaked finch and the large-beaked finch differ? What kinds of foods do you think the different finches eat? With a partner, discuss how the beaks of the differ-ent finch species help them eat different foods.

READING CHECK

1. Explain According to Darwin, why did the different populations of finches become modified over time?

SECTION

1 Developing a TheoryEvolutionary Theory CHAPTER 16



Name Class Date

ARTIFICIAL SELECTION

Later in his life, Darwin became interested in breeding

exotic pigeons. He noted that breeders take advantage

of natural variation within a species. Breeders identify

traits in each generation that they prefer. For example, a

dog breeder may prefer a dog with thicker fur or longer

legs. If these traits can be inherited, breeders can simply

select individuals that have the traits. Darwin called this

process artificial selection.

How Did the Ideas of Others Influence Darwin?Most people in Darwin’s time thought that species

stayed the same forever. However, some scientists

proposed ways that species may change over time.

Darwin was influenced by ideas from the fields of

natural history, economics, and geology.

Individuals and Ideas that Influenced Darwin

Individual(s)and field

Major ideas Importance to Darwin’s theory

Jean Baptiste Lamarck(natural history)

• proposed that organisms change over time as they adapt to changing environments

• thought (incorrectly) that changes due to use or disuse of a trait would be passed on to offspring

suggested that inheritance plays a role in evolution

Thomas Malthus (economics)

• noted that the human population was growing faster than the food supply

• predicted that limited resources would cause deaths from disease, war, or famine

Darwin proposed that all populations, not just human populations, are limited by their environments.

Georges Cuvier (geology)

argued that fossils in rock layers showed:

• differences in species over time

• that species from the past differed from those of the present

showed that species change over time

James Hutton and Charles Lyell (geology)

thought that geologic processes, such as those that form rocks and fossils, work gradually and constantly

showed that Earth’s history was long enough for species to have evolved gradually

2. Infer Why is it important for breeders to select traits that are inherited?

3. List Identify three fields of study that influenced Darwin’s ideas.

4. Identify How was the work of Hutton and Lyell important to Darwin’s theory?

SECTION 1 Developing a Theory continued

Name Class Date

Section 1 Review

SECTION VOCABULARY

artificial selection the human practice of breeding animals or plants that have certain desired traits

evolution generally, in biology, the process of change by which new species develop from preexisting species over time; at the genetic level, the process in which inherited characteristics within populations change over time; the process defined by Darwin as “descent with modification”

1. Describe What were Darwin’s two major contributions to modern evolutionary

theory?

2. Identify How did Darwin explain the similarities among finches in the Galápagos

Islands and in South America?

3. Define What is descent with modification?

4. Infer How does artificial selection provide evidence that species can change over

time?

5. Identify What idea did Lamarck and Darwin share?

6. Describe What evidence from fossils and rock layers influenced Darwin’s ideas?

7. Identify What idea of Malthus did Darwin extend to all populations?



Name Class Date



SECTION

2 Applying Darwin’s IdeasEvolutionary Theory CHAPTER 16


• What does Darwin’s theory predict?

• Why are Darwin’s ideas now widely accepted?

• What were the strengths and weaknesses of Darwin’s ideas?

KEY IDEAS

What Is Natural Selection?Darwin noted that individuals with particular traits

are more likely to survive in their environments. He also

noted that individuals with these traits tend to produce

more offspring than those without the traits do. A trait

that helps individuals survive and reproduce in a given

environment is called an adaptation. Differences in

ability to survive and reproduce are part of the process

of natural selection.

Darwin proposed that natural selection is a cause

of evolution. Evolution is a change in inherited

characteristics in a population from one generation to

the next. Darwin’s explanation is commonly called the

theory of evolution by natural selection. His theory

predicts that, over time, the number of individuals with

beneficial traits will increase in a population.

The Theory of Evolution by Natural Selection

Overproduction Every population is able to produce more offspring than can possibly survive.

1

Variation Variation exists within every population. That is, the individuals of a population have many traits that differ. Much of this variation is in the form of inherited traits.

2

Selection A particular trait can make an individual more likely or less likely to survive and reproduce in its environment. Thus, some individuals survive longer and reproduce more than others in the population do.

3

Adaptation Over time, the traits of those individuals that survive and reproduce will become more common in a population. The population has evolved.

4

READING TOOLBOX

Underline As you read this section, underline the answers to the Key Ideas questions.

READING CHECK

1. Define What is an adaptation?

READING CHECK

2. Identify What mechanism for evolution did Darwin propose?

3. Explain What happens to traits that help individuals survive and reproduce in their environment?

Name Class Date



Applying Darwin’s Ideas continuedSECTION 2

READING CHECK

4. Explain Why are Darwin’s ideas widely accepted today?

READING CHECK

5. Identify For Darwin, what evidence for evolution does the fossil record provide?

6. Identify What do the similarities in the forelimb structures of these vertebrates suggest?

What Does Darwin’s Theory Explain?In his book On the Origin of Species by Means

of Natural Selection, Darwin presented evidence

that evolution happens. He also presented a logical

explanation for how evolution happens. Darwin’s ideas

are widely accepted today because large amounts of

evidence continue to support them.

THE FOSSIL RECORD

Fossils are traces of organisms that have lived in the

past. The fossil record is made up of all the fossils known

to science. Darwin noticed patterns in the fossil record

that suggested that species change over time. However,

he also knew that the pattern had gaps. The conditions

that create fossils are rare. Thus, we will never find

fossils of every species that ever lived. The fossil record

will grow but will never be complete.

ANATOMY

Scientists can compare the internal structures,

or anatomy, of different species to see the results of

evolution. Evolution explains the similarities in internal

structures. Similar internal structures are evidence of

how species are related. Structures that are similar in

two or more species and were inherited from a common

ancestor are called homologous structures.

PenguinBat

Alligator Human

Although they look very different from one another on the outside, the forelimbs of these four vertebrates have very similar groups of bones. This suggests that all vertebrates descended from a common ancestor.

Name Class Date



SECTION 2 Applying Darwin’s Ideas continued

BIOGEOGRAPHY

Biogeography is the study of the locations of organisms

around the world. Darwin noticed similarities in three

species of large birds: the rhea in South America, the ostrich

in Africa, and the emu in Australia. These species are

similar in size, shape, eating habits, and habitats. Darwin’s

observation was evidence that similar environments shape

the evolution of organisms in similar ways.

Sometimes geography separates populations. For

example, a population may split into two groups that live

on two different islands. Over time, the two groups may

evolve in different ways.

DEVELOPMENTAL BIOLOGY

Scientists may compare the development of embryos

of different species to look for similar patterns and

structures. For example, scientists have found that

all vertebrate embryos have tails at some time in their

development. This similarity most likely comes from an

ancestor that vertebrate species share.

BIOCHEMISTRY

A comparison of DNA or amino-acid sequences

shows that some species are more genetically similar

than others. Organisms with similar sequences are more

closely related than are organisms with more differences

in their sequences.

What Are the Strengths of Darwin’s Theory? Darwin’s ideas are widely accepted because of their

strengths:

• His work is supported by, and helps explain, a largeamount of data.

• He developed a logical and testable mechanism—naturalselection—to explain the process of evolution.

• He showed that variation could serve as a starting pointfor evolution.

There was only one major weakness in Darwin’s

theory. Inherited variation was important to the theory of

natural selection. However, because he knew little about

genetics, Darwin could not propose a clear mechanism

for inheritance.

7. Apply Concepts Why is Darwin’s explanation of evolution a theory and not a hypothesis?

8. Apply Concepts Horsesshare a larger percentage of their genes with dogs than with earthworms. What does this suggest?

Name Class Date



Section 2 Review

SECTION VOCABULARY

adaptation the process of becoming adapted to an environment; an anatomical, physiological, or behavioral change that improves a population’s ability to survive

fossil the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock

homologous describes a character that is shared by a group of species because it is inherited from a common ancestor

natural selection the process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individualsdo; a theory to explain the mechanism of evolution

1. Identify What does Darwin’s theory of evolution by natural selection predict?

2. List What are the four steps of Darwin’s theory of evolution?

3. Summarize Complete the table below to summarize how evidence supports

Darwin’s theory of evolution.

Source of evidence What the evidence indicates

Fossil record

Anatomy

Biogeography

Developmental biology Species with embryos that show similar patterns of development probably share a common ancestor.

Biochemistry

4. Identify What are three major strengths of Darwin’s theory of evolution by natural

selection?



Name Class Date

SECTION

3 Beyond Darwinian TheoryEvolutionary TheoryCHAPTER 16


• How has Darwin’s theory been updated?

• At what scales can evolution be studied?

KEY IDEAS

How Has Darwin’s Theory Been Updated?Since Darwin’s time, new discoveries, particularly in

the field of genetics, have helped explain the evolution

of species. Scientists have modified parts of Darwin’s

theory and added to it. However, most recent discoveries

support his theory.

What Are Microevolution and Macroevolution? Microevolution refers to changes in the genes of

populations.

Processes of Microevolution

Process Description

Naturalselection

Individuals with a particular trait are more likely to survive and reproduce than those without the trait.

Migration Individuals with different alleles may move into or out of a population.

Matechoice

Parents that are limited or selective in their choice of mates pass a limited set of traits to the next generation.

Mutation Mutations are the source of completely new alleles.

Geneticdrift

Random effects of everyday life can cause differences in survival and reproduction of individuals.

Macroevolution refers to the appearance of new

species over time. The formation of a new species is

called speciation.

Patterns of Macroevolution

Pattern Description

Convergentevolution

Species living in similar environments may evolve similar adaptations.

Coevolution Two or more species that live in close contact may affect how each species evolves.

Adaptiveradiation

A species may give rise to many new species after it enters an environment that contains few other species.

Extinction All members of a lineage die off or fail to reproduce.

Gradualism The formation of some new species requires many small changes to build up gradually over time.

Punctuatedequilibrium

Many species remain stable, or unchanged, for a long time. If environmental changes create new pressures, many new species evolve rapidly.

READING TOOLBOX

Make Flashcards After you read this section, make flashcards that identify the processes of microevolution and macroevolution. Write the name of the process on one side of the card. Describe the process in your own words on the other side of the card. Be sure to identify whether each process is an example of microevolution or macroevolution.

1. Identify Which microevolutionary process involves individuals moving into or out of a population?

BackgroundRecall that a species is a group of organisms that are closely related and that can mate to produce fertile offspring.

Brainstorm With a partner, brainstorm examples of species that show convergent evolution. What adaptations do they have that are similar?



Name Class Date

Section 3 Review

SECTION VOCABULARY

speciation the formation of a new species as a result of evolution

1. Identify Name one field of study that has contributed discoveries that support

Darwin’s theory of evolution.

2. Compare How does microevolution differ from macroevolution?

3. Infer How does migration cause a change in the genes in a population?

4. Compare How does genetic drift differ from natural selection?

5. Identify According to the punctuated equilibrium model of speciation, what

causes many new species to evolve rapidly?

6. Analyze Relationships How do you think adaptive radiation and extinction are related?

7. Make Conclusions A scientist observes that a particular species of butterfly has

a very long tongue. The butterfly feeds on a flower that has nectar at the bottom

of a long tube. What pattern of macroevolution best explains the traits that the

scientist observed? Explain your answer.

chapter 16 evolutionary theory section 1 … · his ideas about evolution? evolution is the process...

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