Transcript Chapter 4

Chapter 4
Population Changes
Preview
Section 1 Change over Time
Section 2 How Do Population Changes Happen?
Section 3 Natural Selection in Action
Concept Mapping
Chapter 4
Section 1 Change over Time
Bellringer
The cockroach originated on Earth over 250 MYA
and is thriving today worldwide. A giant deer 2 m
tall first appeared <1 MYA and became extinct
~11,000 years ago. Why did one animal thrive
while the other perished?
Record your answer in your science journal.
Chapter 4
Section 1 Change over Time
Objectives
• Identify two kinds of evidence that show that organisms
have changed over time.
• Identify how the fossil record shows that changes in the
kinds of organisms in the environment have been
occurring over time.
• Describe one pathway through which a modern whale
could have arisen from an ancient mammal.
• Explain how comparing organisms can provide
evidence that they have ancestors in common.
Chapter 4
Section 1 Change over Time
Differences Between Organisms
• Adaptation: a characteristic that helps an organism
survive and reproduce in its environment
• Physical adaptations:
• fur
• scales
• gills
• bioluminescence
• Behavioral adaptations:
• food finding
• self-protection
• reproduce
Chapter 4
Changes in Genetic
Variation page 88
• Genetic bottleneck: reduced number of
characteristics within a population
• Typically occurs if a population decreases
in numbers rapidly – many traits may be
lost because members of population with
those characteristics died
• Population has become genetically similar,
susceptible to birth defects/genetic
diseases EX: Florida panthers
Chapter 4
Section 1 Change over Time
• Individual organisms sharing same
characteristics might be members of same
species.
• Species: group of organisms that can mate
w/ one another to produce fertile offspring.
• Population: groups of individuals of same
species living in same area
Chapter 4
Section 1 Change over Time
Differences Between Organisms, continued
Since life first appeared on Earth:
• many species have died out
(extinction)
• many new species have appeared
Chapter 4
• Scientists observe that inherited characteristics in
populations change over time.
• May happen in relatively short periods of time, such
as MRSA or insecticide resistant insects.
• Scientists think that as populations change over time,
new species form.
Chapter 4
Section 1 Change over Time
Evidence of Change over Time
• Sediments laid down over time contain remains of
ancient organisms. (sedimentary rock)
• Older layers are deeper, contain older organisms.
• Earth ~4.6 billion year old
Chapter 4
• Fossils: remains or imprints of onceliving organisms found in layers of
rock (typically sedimentary)
• Examples of fossils vary from
footprints to complete organisms.
Chapter 4
Section 1 Change over Time
Evidence of Change over Time, continued
• By studying fossils, scientists have made timeline of life
known as the fossil record.
• organizes fossils by their estimated ages and
physical similarities.
• Comparing organisms in fossil record can reveal how
organisms have changed over time.
Chapter 4
Section 1 Change over Time
Evidence of Ancestry
• Scientists observe common characteristics in all life
 suggests all living species descended from
common ancestors.
• Evidence of common ancestors  found in fossils
and in living organisms.
Chapter 4
Section 1 Change over Time
Evidence of Ancestry, continued
• Drawing Connections
• Scientists examine fossil record to figure
out relationships between extinct and
living organisms.
• Scientists draw models that show
proposed relationships between ancient
and modern organisms.
Chapter 4
Section 1 Change over Time
Examining Organisms
• Case Study: Origins of the Modern Whale
Scientists think ancient ancestor of whales was
probably mammal that lived on land, could run on 4
legs.
• Comparisons between modern whales and large
number of fossils have supported this hypothesis.
Chapter 4
Evidence of Whale Origins: A (pg. 104)
Chapter 4
Evidence of Whale Origins: B (pg. 105)
Chapter 4
Examining Organisms
Walking Whales
• Each new species in fossil record of whale has shared
traits with an earlier species.
• Some species had new traits that were passed on to
later species. In all cases, organisms had traits that
allowed them to survive in their unique environment.
• Modern whales have hip bones  link to their ancient
walking ancestors.
Chapter 4
Whale Evolution video
Chapter 4
Section 1 Change over Time
Comparing Organisms
• Comparing Skeletal Structures The structure & order of
bones of human arm are similar to those of front limbs of
cat, dolphin, and bat.
(homologous structures: similar anatomical structures
with similar developmental and embryological origins
having different functions, suggesting common ancestor)
• These similarities suggest cats, dolphins, bats, and
humans had common ancestor.
Chapter 4
Section 1 Change over Time
Homologous structures
Chapter 4
Section 1 Change over Time
Comparing DNA Molecules
• Scientists also compare organisms at molecular level.
• Species having more DNA in common:
• more closely related
• shared common ancestor more recently
Fact that all existing species have DNA supports theory
that all species share a common ancestor.
Chapter 4
Section 2 How Do Population
Changes Happen?
Bellringer
The following are traits that almost all humans have in
common: upright walking, hair, fingerprints, binocular
vision, and speech. 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 science journal.
Chapter 4
Section 2 How Do Population
Changes Happen?
Objectives
• Describe how some finch species of the Galapagos
Islands developed adaptations in response to their
environment.
• Describe the four parts of Charles Darwin’s process
of natural selection.
• Explain how variation in each species can occur.
Chapter 4
Section 2 How Do Population
Changes Happen?
Charles Darwin
• 1800s:
• scientists beginning to see evidence of
change in fossil record
• no one able to explain how change
happened until Charles Darwin.
Chapter 4
Charles Darwin
• 5-year voyage around world aboard
ship HMS Beagle
• worked as a naturalist
• observations helped him form
hypothesis about how change happens
Chapter 4
Section 2 How Do Population
Changes Happen?
Darwin:
• collected thousands of plant and animal samples
• observations made on Galápagos Islands west of
Ecuador  especially important to his hypothesis.
Chapter 4
Darwin’s Journey to Galapagos
Chapter 4
Section 2 How Do Population
Changes Happen?
Darwin’s Finches
• noticed that finches of Galápagos Islands were much like
those in Ecuador (600 miles / 966 km away)
• finches on each island differed from those on other islands.
Chapter 4
Chapter 4
Section 2 How Do Population
Changes Happen?
Darwin’s Thinking
• hypothesized island finches descended from
South American finches, likely blown from
mainland (600 miles) in a storm.
(Finches can’t fly long distances.)
• suggested over many generations  finches
developed adaptations for various island
environments  avoiding competition for limited
food sources
Chapter 4
Natural Selection: Examples from the Galapagos
Chapter 4
Section 2 How Do Population
Changes Happen?
Darwin’s Thinking, continued
• In Darwin’s time:
• farmers & breeders:
• had produced many kinds of farm animals,
plants.
• these plants, animals had desired traits
• Trait: genetically determined characteristic
• Ex: large corn ears, heavy milk production
Chapter 4
Section 2 How Do Population
Changes Happen?
• selective breeding: practice by which humans
select plants or animals for breeding based on
desired traits
• Most pets have been bred for their desired traits.
• Dogs: German shepherds, Chihuahuas, etc
• Horses: Arabians, Clydesdales, etc
Chapter 4
Selective
breeding:
Felis
domesticus
Chapter 4
Section 2 How Do Population
Changes Happen?
Darwin’s Ideas About Population
• influenced by essay (Thomas Malthus) -described why
human populations do not grow uncontrollably.
• knew populations of all species are limited by starvation,
disease, competition, and predation.
• reasoned offspring of survivors inherit traits  help
offspring survive in their environment.
Chapter 4
Section 2 How Do Population
Changes Happen?
Darwin’s Thinking, continued
Ideas About Earth’s History
New ideas about age of Earth (Charles Lyell’s Principles
of Geology) provided enough time for adaptations to
occur  supported Darwin’s idea that species change
over time.
**Current evidence for Earth’s age = ~ 4.6 billion years
Chapter 4
Section 2 How Do Population
Changes Happen?
Darwin’s Theory of Natural Selection
• 1859: Darwin published On the Origin of Species by
Means of Natural Selection.
• In his book, Darwin proposed the hypothesis (NOW a
theory) that change in populations happens through
natural selection.
Chapter 4
• Natural selection: process by which
organisms better adapted to their
environment survive and reproduce more
successfully than less well adapted
organisms
Chapter 4
Intro to Darwin’s Theory
Chapter 4
Copyright © by Holt, Rinehart and Winston. All rights reserved.
Chapter 4
Section 2 How Do Population
Changes Happen?
Genetics and Inherited Traits
Variation happens as result of exchange of genetic
information passed from parent to offspring.
• Some genes make organism more likely to survive to
reproduce.
• Selection happens when only organisms carrying
these genes survive to reproduce.
Chapter 4
The Evidence for Adaptation Over Time
Chapter 4
Section 3 Natural Selection in Action
Bellringer
A mnemonic device is a trick that can help you
remember words. Write down the four steps of
natural selection. Then create a mnemonic device
to help you remember each step by using the first
letter of the main word from each step as the first
letter of a word in a phrase that is easy for you to
remember.
Write your answer in your science journal.
Chapter 4
Section 3 Natural Selection in Action
Objectives
• Give two examples of how natural selection can
result in an adaptation that helps an organism
survive.
• Outline the process of speciation.
Chapter 4
Section 3 Natural Selection in Action
Changes in Populations
• The theory of natural selection explains how a
population changes in response to its environment.
• Well-adapted individuals will likely survive and
reproduce.
Chapter 4
Section 3 Natural Selection in Action
• Scientists think hunting in Uganda is affecting
Uganda’s elephant population.
• Elephants hunted for tusks (valuable ivory).
• Fewer tusked elephants survive to reproduce
 more tuskless elephants survive.
• Tuskless elephants pass tuskless trait to
offspring.
Chapter 4
Section 3 Natural Selection in Action
Changes in Populations
Insecticide Resistance
• Insect populations become resistant to insecticide:
• produce many offspring
• have short generation time
Generation time: average time between one generation
to the next.
Chapter 4
Chapter 4
Section 3 Natural Selection in Action
Competition for Mates
• Survival of individuals does not guarantee
survival of a species.
• For organisms that reproduce sexually,
competition for mates can select for
adaptations.
• Typically, best adapted will reproduce 
healthiest adults produce healthiest
offspring.
Chapter 4
Section 3 Natural Selection in Action
Forming a New Species
Sometimes, drastic changes that can form a new species take
place.
• A new species may form after a group becomes
separated from the original population.
Speciation: formation of new species as a result of change
over time
Chapter 4
Agents of Adaptation Over Time
Chapter 4
SPECIATION
• Separation
• Adaptation
• Division
Chapter 4
Section 3 Natural Selection in Action
Forming a New Species, continued
Separation Speciation often begins when part of
population becomes separated from rest.
Adaptation Populations constantly undergo natural
selection. After two groups have separated, natural
selection continues to act on each group.
• If environmental conditions for each group differ, each
groups’ adaptations will differ.
Chapter 4
Section 3 Natural Selection in Action
Forming a New Species, ctd
Division Over many generations, two separated groups of
a population may become very different through natural
selection.
• Even if geological barrier is removed, groups reunited
 may no longer be able to interbreed.
• If they cannot interbreed  no longer same species.
Chapter 4
Development of Galápagos Finch Species
Chapter 4
Chapter 4
Section 3 Natural Selection in Action
Species
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Visual Concept