___
___
___
Natural selection
Chapter 7
Charles Darwin
Section 2 How Does Evolution
Happen?
___
___
Natural Selection
Natural selection is when nature selects the winners and losers in life
Evolution is a gradual change in an organisms genotype and
phenotype
Mutations in the DNA code can affect natural selection
A species is a group of organisms that nature is responsible for
grouping together
Evolution is a very rapid process
___
The theory of evolution helps explain how different plants, animals,
animals,
and microorganisms are related
___
There is very little evidence to support natural selection.
___
The Galapagos is a large colorful bird
___
Evolution is a fact that we know happened
Chapter 7
Charles Darwin
Section 2 How Does Evolution
Happen?
• Darwin’s Excellent Adventure 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.
Chapter 7
Section 2 How Does Evolution
Happen?
Chapter 7
Section 2 How Does Evolution
Happen?
Darwin’s Theory of Natural Selection
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.
• What Is Natural Selection?. Individuals that are better
adapted to their environment survive and reproduce more
successfully than less well adapted individuals.
•Darwin proposed the theory that evolution happens
through a process that he called natural selection
• 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.
Natural Selection
Steps for natural selection
Natural Selection—
Selection—individuals best suited to compete, survive, and
reproduce in their environment will pass on favorable traits (genes)
(genes)
to the next generation.
1. More offspring are produced than can survive.
Variation—
Variation—difference between individuals in a species
2. Individuals vary genetically.
Adaptation—
Adaptation— a characteristic that increases an organisms chance to
survive in its environment or reproduce
3. Individuals struggle to survive.
Evolution—
Evolution—gradual change in a species over time that makes them
more suited to the environment
Niche—
Niche—a place in the environment that an organism uses
4. The individuals with variations that best suit their
environment (fit)
survive & reproduce
 Natural selection presentation
 The lawn mower
http://caspar.bgsu.edu/~courses/Ethology/Videos/Selection.mov
http://caspar.bgsu.edu/~courses/Ethology/Videos/Selection.mov
http://www.biologyinmotion.com/evol/index.html
 PBS camouflage
Chapter 7
Section 2 How Does Evolution
Happen?
Evidence of Natural Selection
 Fossils
 Vestigial structures –tail bone Similar
body structures
 Homologous structuresstructures-
 Similar early development
 Similar DNA (table on pg 170)
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Fossil record
“Irish elk”
mastodon
Chapter 7
Section 1 Change over Time
Fossils and Vestigital Structures
Examining Organisms
• Case Study: Evolution of the Whale Scientists
think that the ancient ancestor of whales was
probably a mammal that lived on land and that could
run on four legs.
• Walking Whales The organisms shown on the next
slide form a sequence between ancient four-legged
mammals and modern whales. Several pieces of
evidence indicate that these species are related by
ancestry.
Chapter 7
Section 1 Change over Time
Chapter 7
Section 1 Change over Time
Whale
Evolution

Section 1
Chapter 7
Comparing Organisms
Change over Time
Chapter 7
Section 1 Change over Time
• Comparing Skeletal Structures The
structure and order of bones of a human arm
are similar to those of the front limbs of a
cat, a dolphin, and a bat. These similarities
suggest that cats, dolphins, bats, and
humans had a common ancestor.
Homologous Structures
Early Development
Chapter 7
Section 1 Change over Time
Chapter 7
Section 2 How Does Evolution
Happen?
Comparing Organisms, continued
Bellringer
• Comparing DNA The greater the number of
similarities in DNA between species, the more
closely those two species are related through a
common ancestor.
Upright 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?
• The fact that all existing species have DNA
supports the theory that all species share a common
ancestor.
Record your responses in your science journal.
Chapter 7
Section 2 How Does Evolution
Happen?
Objectives
Chapter 7
Section 3 Natural Selection in Action
Bellringer
• 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.
Write 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 science journal.
• Relate genetics to evolution.
Chapter 7
Section 3 Natural Selection in Action
Chapter 7
Section 3 Natural Selection in Action
Changes in Populations
Objectives
• Give three examples of natural selection in action.
• 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.
• Outline the process of speciation.
• 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.
Chapter 7
Section 3 Natural Selection in Action
Chapter 7
Section 3 Natural Selection in Action
Changes in Populations, continued
Changes in Populations, continued
• 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.
Chapter 7
Section 3 Natural Selection in Action
Chapter 7
Section 3 Natural Selection in Action
Forming a New Species
• 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.
Chapter 7
Section 3 Natural Selection in Action
Forming a New Species, continued
• 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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 7
Section 3 Natural Selection in Action
Forming a New Species, continued
• 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.
Chapter menu
 http://www.biologyinmotion.com/evol/index.html
http://www.biologyinmotion.com/evol/index.html
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 7
Section 1 Change over Time
Chapter 7
Section 3 Natural Selection in Action
Species
Bellringer
The cockroach first appeared on Earth over 250
million years ago and is thriving today all over the
world. A giant deer that was 2 m tall and had
antlers up to 3.6 m wide first appeared less than 1
million years ago and became extinct around
11,000 years ago. Why do you think one animal
thrived and the other one perished?
Click below to watch the Visual Concept.
Visual Concept
You may stop the video at any time by pressing
the Esc key.
Record your answer in your science journal.
Chapter 7
Section 1 Change over Time
Chapter 7
Section 1 Change over Time
Differences Among Organisms, continued
Differences Among Organisms
• 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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
• 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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 7
Section 1 Change over Time
Evolution
Section 1 Change over Time
Evidence of Change over Time
Click below to watch the Visual Concept.
• Fossils The remains or imprints of once-living
organisms found in layers of rock called fossils.
Visual Concept
You may stop the video at any time by pressing
the Esc key.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
FYI
x
Section 1 Change over Time
Evidence of Ancestry
• Order of Life The fossil record provides evidence
about the order in which species have existed.
• Drawing Connections Scientists have named and
described hundreds of thousands of living and
ancient species. Scientists use information about
these species to sketch out a “ tree of life” that
includes all known organisms.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.
• The Fossil Record 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.
Chapter menu
Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.