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Chapter 10 Evolution
The Big Idea Biological evolution explains how __________change
over time.
Section 1 Change over Time
Key Concept Independent lines of evidence from_________, fossils,
and comparative anatomy provide the bases for the theory of
evolution.
Differences Between Organisms
• Each type of ___________has a unique set of characteristics.
• A characteristic that helps an organism survive and reproduce in its
environment is called an_____________.
• Adaptations can be physical, such as the color of fur, or they can be
_____________, such as a way of finding food.
• A group of organisms with the same set of adaptations may be the
same___________.
• A species is a group of organisms that can mate with one another to
produce __________offspring.
• A group of organisms of the same species living in the same place is
called a___________.
• There are currently millions of ____________species around the world, from
bacteria to plants and animals.
Do Species Change over Time?
• Over time, many species have lived and died out, and many new
species have appeared. Newer species are descended from ____________
species.
• Scientists have observed that the characteristics of species ________
over time.
• The characteristics of populations change over time as well. As they
change, a new species may____________.
• The process in which populations change over time is called_________.
Evidence of Changes over Time
• Evidence that organisms have changed over time is buried in
____________rock.
• When sediments like _________or clay particles settle on a dead organism, a
fossil may form within sedimentary rock.
• Fossils are the remains or imprints of once-living organisms found in
_________of rock.
• All of the fossils that have been found so far make up the fossil record.
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,
The fossil record is a ___________of life on Earth.
• Fossils found in newer layers of Earth’s crust are _________to present-day
organisms.
• Fossils from__________, older layers of rock are less similar to living
organisms. Comparing organisms in the fossil record shows changes over time.
Evidence of Ancestry
• The fossil __________provides evidence abut the order in which species
have lived. The fossils can be used to assemble a record of ancestry.
• All organisms share some characteristics, so it is believed that all
organisms are descended from ___________ancestors.
• There is evidence of common ancestors in fossils as well as living
__________.
• Scientists may draw _____________diagrams to show how species are
related. These diagrams are a bit like family trees.
• A branching diagram can be used to show that __________share a common
ancestor with hippopotamuses, and share common ancestors with
many other hoofed mammals as well.
Examining Organisms
• At first glance, whales may seem similar to fish. But whales have all the
characteristics of a__________.
• Scientists believe that the ancient ancestor of whales was a _________
mammal. A more recent ancestor was a mammal that spent some time
in water and some time on land.
• There is fossil evidence to support this hypothesis.
• Whales have no hind legs, but they do have ___________bones. Scientists
believe they inherited these bones from a walking ancestor.
• At each step along the evolutionary pathway, there are similarities
between __________organisms and the organisms that followed.
• Successful new traits were often passed on to future species.
Comparing Anatomy
• The study of comparative anatomy compares similar _____________of
organisms. Comparative anatomy provides evidence for evolution.
• For example, despite function and appearances, there are many
similarities between the bones of a human arm, a cat leg, a dolphin
__________, and a bat wing.
Comparing DNA Molecules
• Scientists also compare the DNA of different organisms. Similarities in
DNA between organisms suggest a common___________.
• The greater the number of similarities between the DNA of any two species, the
more recently the two species shared a common ancestor.
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,
Section 2 How Does Evolution Happen?
Key Concept After making observations and analyzing evidence,
Charles Darwin concluded that natural selection is the mechanism of
evolution.
Charles Darwin
• In the 1800s, some scientists were beginning to see evidence of
evolution, but no one could explain how evolution occurred until Charles
Darwin.
• As the naturalist aboard the Beagle, Darwin spent five years studying
nature all around the world.
• His observations on this voyage helped him develop a theory about how
evolution happens.
Darwin’s Journey
• During his journey, Darwin visited the Galapagos Islands, 965 km west
of Ecuador.
• Darwin noticed that the plants and animals were somewhat different on
the islands than they were on the mainland of South America.
• He noticed that the beaks of the finches were notably different, even
from island to island.
• The shapes of the different finch beaks were adapted to the way each
finch gets food.
Darwin’s Thinking
• Darwin hypothesized that the island finches were descendents of South
American finches.
• He suggested that the first finches were blown to the islands in a storm.
• Over many generations, the isolated finches evolved adaptations
unique to each island environment.
Ideas About Breeding
• In Darwin’s time, farmers and breeders had already developed plants
and animals with many different characteristics.
• The plants and animals had desirable traits. A trait is a form of an
inherited characteristic, such as bright red for fruit color, or largeness for
pig size.
• The practice by which humans select plants or animals for breeding
based on desired traits is called selective breeding.
• Pets, such as dogs and cats, are also the result of selective breeding.
• Selective breeding shows that traits of organisms can change, and that
traits can spread through populations.
Ideas About Population
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,
• Darwin’s thinking was influenced by the works of others, including
Thomas Malthus.
• In his work, Malthus proposed that human populations grow more
quickly than their food supply. Factors such as disease and starvation
help to control growth.
• Darwin reasoned that these ideas applied to other organisms as well.
• Darwin knew that all populations are limited by starvation, competition,
disease, and predation.
• Only a limited number of individuals live to reproduce. These individuals
must have traits to help them survive.
• Some of these traits, Darwin reasoned, would be passed on to their
offspring.
Ideas About Earth’s History
• During Darwin’s time, most geologists thought the Earth was very
young.
• The geologist Charles Lyell wrote Principles of Geology, a book that
presented evidence that Earth was formed by natural processes over a
long period of time.
• Darwin reasoned that if Earth were very old, then there would be
enough time for organisms to slowly change.
Darwin’s Theory of Natural Selection
• Darwin continued to struggle with his ideas for 20 years after his time
on board the Beagle.
• When he learned that another scientist was about to publish similar
ideas, he finally published his work.
• In 1859, Darwin published the now famous book On the Origin of
Species by Means of Natural Selection.
• His book was a breakthrough because he proposed a method for
evolution: natural selection.
• Natural selection is the mechanism, or process, by which organisms
that are better adapted to their environment survive and reproduce
more successfully than less well adapted organisms do.
The Four Parts of Natural Selection
• The process of natural selection has four steps.
• Overproduction All species tend to produce more offspring than can
survive.
• Inherited Variation Within a population are many individuals, each
with a slightly unique set of traits.
• Struggle to Survive There are limited amounts of resources for each
individual, as well as diseases and predators.
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,
• Successful Reproduction Individuals with the best traits for their
environment survive to have more offspring than individuals with less
favorable traits.
Genetics and Evolution
• Darwin knew that organisms inherit traits, but not how they inherit traits.
He observed variation in populations, but not how that variation occurs.
• Today we know that variation is due to genetic differences, and that
these genes are passed from parent to offspring.
ANSWERS SECTION 2
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,
Section 3 Natural Selection in Action
Key Concept Natural selection explains how populations adapt to
changes in their environment and why some species become extinct.
Genetic Variation
• For natural selection to occur, a population must have a variety of traits.
The traits are determined by the genes, or genetic variation, within the
population.
• The genetic variation of a population is a measure of how much
individuals in a population differ genetically.
• The greater the amount of genetic variation, the greater the range of
traits within a population.
• Populations with high genetic variation are more likely to have some
individuals with favorable traits, even if environmental conditions
change.
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• Populations with low genetic variation are less likely to survive changes
in the environment.
Environmental Factors
• Environmental factors determine whether a trait is favorable for survival
or unfavorable.
• Environmental factors are the conditions in an environment that affect
the organisms that live there.
• In a green environment, green feathers might be a favorable trait. In a
brown environment, green feathers might be an unfavorable trait.
Forming a New Species: Separation
• The formation of a new species as a result of evolution is called
speciation.
• Speciation often begins when a part of a population becomes separated
from the rest.
• Separation may be caused by changes in the environment, such as a
newly formed canyon, lake, or mountain range.
Forming a New Species: Adaptation
• Once separated, natural selection continues to act on the different
groups.
• If the environments are different for the two groups, they will evolve
different adaptations for their unique conditions.
• For example, two groups of birds may evolve different beaks to eat the
unique types of seeds in their environments.
Forming a New Species: Reproductive Isolation
• Over time, the two groups may evolve to have very different traits.
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,
• If the groups are reunited, they may no longer be able to interbreed. If
so, they have undergone reproductive isolation.
• If they can no longer interbreed, the two groups are now different
species.
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Review Tip
Describing Concepts How would you describe the process of speciation
to another student? Be sure to describe separation, adaptation, and
reproductive isolation. Write or say your explanation.
Extinction
• If environmental factors change, populations may be able to evolve and
adapt to their new conditions.
• If environmental factors change drastically, then populations may not be
able to adapt. The species may become extinct.
• A species becomes extinct when all the individuals of a species have
died.
Increased Competition
• If the resources needed for survival become more scarce, competition
increases for the remaining resources.
• If resources such as water, food, shelter or space become so scarce
that none of the individuals of a species are able to survive, the species
may become extinct.
New Predators
• Sometimes a new predator moves into an area, or is introduced by
humans.
• The prey populations may not have the necessary adaptations to
escape the new predator.
• The new predator may cause extinction for a species that cannot
survive.
Loss of Habitat
• Organisms get the resources they need from the habitats they live in.
• Human activities such as timber harvesting or development can destroy
habitats. Natural disasters can also destroy habitats.
• A species may not survive in the changed habitat. If they lack the
adaptations to move and survive in a new habitat, the species may
become extinct.
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Review Tip Wrap-Up
Think about the methods you have used to study the concepts in this
chapter. Which types of Review Tips are the most helpful to you? What
types of concepts do they help you study? Think about review methods
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,
you can use when you are studying.
Answers section 1
species, populations, structures, layers, evolution, organisms, develop,
sedimentary, change, different, older, history, deeper, adaptation, whales, land,
hip, branching, population, common, ancestor, fertile, flipper, sand, organism,
behavioral, record, mammal, geology, similar, older,