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Anu Singh-Cundy • Gary Shin
Discover Biology
SIXTH EDITION
CHAPTER 16
The Evolutionary History of Life
© 2015 W. W. Norton & Company, Inc.
CHAPTER 16
The Evolutionary History of Life, Part 1
PUZZLING FOSSILS IN A FROZEN WASTELAND
16.1 Macroevolution: Large-Scale Body Changes
16.2 The Fossil Record: A Guide to the Past
The fossil record is incomplete
Fossils reveal that whales are closely related to a group of hoofed mammals
16.3 The History of Life on Earth
The first single-celled organisms arose at least 3.5 billion years ago
Multicellular life evolved about 650 million years ago
Colonization of land followed the Cambrian explosion
16.4 The Effects of Plate Tectonics
16.5 Mass Extinctions: Worldwide Losses of Species
CHAPTER 16
The Evolutionary History of Life, Part 2
16.6 Rapid Macroevolution through Differential Gene Expression
16.7 Phylogenetics: Reconstructing Evolutionary Relationships
The Linnaean system of biological classification reflects evolutionary history
BIOLOLGY MATTERS: IS MASS EXTINCTION UNDER WAY?
APPLYING WHAT WE LEARNED: WHEN ANTARCTICA WAS GREEN
Puzzling Fossils in a Frozen Wasteland
• Paleontologists have uncovered signs indicating that life in Antarctica once included
dinosaurs and other reptiles, mammals and flightless birds, ferns and enormous trees,
amphibians, freshwater fishes, and aquatic beetles.
The Earth Is Billions of Years Old
•
In the nineteenth century, Lord
Kelvin estimated the age of
Earth at no more than ~100
million years.
•
Darwin recognized that while
natural selection is potent
enough to generate adaptations
in organisms, very large
timescales would be necessary
to explain the great diversity of
body plans observed in nature.
•
Radioisotopes are unstable forms
of elements that decay to more
stable forms at a constant rate
over time.
•
History of Earth as a 24-hour day:
Dinosaurs evolved just before 11:00 PM, and humans, just a minute
before midnight .
The application of isotope
studies to geology brought the
current estimate of Earth’s age
to approximately 4.6 billion
years.
The Climate and Geology of Our Planet Have Changed over
Hundreds of Millions of Years, Causing Dramatic Changes in
the Life-forms on Earth
• In the time span since Earth was formed,
known as geologic time, both the land and
climate have gone through large changes
over and over again.
• Geological time provides sufficient time for
the process of natural selection to create
large-scale changes in organisms.
Hot plumes of liquid rock from Earth’s
interior can rise to the surface and push the
continents away from each other, as at this rift
in Iceland.
• About 1.7 million species have been
described, and millions more await
discovery.
• However, present-day species are thought
to represent less than 1 percent of all the
species that have ever lived because many
life forms have become extinct.
Macroevolution Describes
Large-Scale Alterations in
Form
• Organisms differ radically in form, in
embryological development, in body
plans, in behavior, and in ecology.
• Macroevolution refers to large-scale
changes in organisms, generally occurring
over millions of years.
The body plan of whales has
been radically altered by
adaptations to aquatic life
compared with the body plan
of their terrestrial ungulate
(hoofed) ancestors.
The Fossil Record Documents the History of Life on Earth
•
•
•
Fossils are the preserved remains or impressions of individual organisms that lived in the past, and are
often found in sedimentary rock.
Fossils provide evidence that past organisms were unlike organisms alive today, that many forms have
disappeared from Earth completely, and that life has evolved through time.
Older fossils are found in deeper, older rock layers. The order in which organisms appear in the fossil
record agrees with our understanding of evolution based on other evidence, providing strong support
for evolution.
A Fossil’s Age Can Be Estimated Using
Radioisotopes
• Carbon dating can reveal the age of relatively recent fossils. For a given amount of the
radioisotope carbon-14 (14C), half of the total decays to the stable element carbon-12 every
5,730 years. By measuring the amount of 14C that remains in a fossil, scientists can estimate
the age of the fossil.
• Carbon-14 can be used to date only relatively recent fossils: too little 14C remains to date
fossils formed more than 70,000 years ago.
• Other radioisotopes reveal the age of the
more ancient fossils. Elements such as
uranium-235, which has a half-life of 700
million years, can be used to date much
older materials.
• If a fossil does not contain any
radioisotopes, methods like carbon or
uranium dating enable us to determine an
approximate date for the fossil by dating
rocks found above and below the fossil.
The Fossil Record Is Not Complete
The fossil record contains many gaps because:
• Most organisms decompose rapidly after death and do not form
fossils.
• Other have few hard parts and do not fossilize well for that reason.
• Organisms may not live near areas where sediments typically form.
• Those fossils that are formed can be destroyed by common geologic
processes such as erosion and extreme heat or pressure.
• Fossils are hard to find.
It takes a unique set
of circumstances to
form and preserve
fossils, and for fossils
to be discovered.
Fossils Reveal That Whales Are Closely
Related to a Group of Hoofed Mammals
•
Whales have a relatively complete
fossil record, which enables scientists
to observe many transitional forms
that document their evolutionary past.
•
Whales show the greatest DNA
similarity to artiodactyls, which are
even-toed, hoofed land mammals
(such as hippos, camels, and giraffes).
The History of Life on Earth: Single-Celled Life
Appeared by 3.5 Billion Years Ago
• The oldest known rocks on Earth (3.8
billion years old) contain carbon
deposits that hint at life.
• Cell-like structures have been found
in stromatolites that formed
3.5 billion years ago.
• DNA analysis also supports the idea
that life had appeared on Earth by
3.5 billion years ago.
Stromatolites are sediment mounds
containing fossilized microorganisms.
• The first life-forms were prokaryotes.
• Eukaryotes are first seen in the fossil
record at about 2.1 billion years ago.
The Evolution of Oxygen-Producing Photosynthesis Was One
of the Most Important Events in the History of Life on Earth
• Earth’s atmosphere initially
contained almost no oxygen.
• Roughly 2.8 billion years ago, a
group of bacteria evolved a type of
photosynthesis that releases oxygen
as a by-product.
• As a result, oxygen began to
accumulate in the atmosphere.
• Eukaryotes, with their larger cells
and therefore greater energy needs,
evolved when oxygen reached at
least 2–3 percent of present-day
levels.
• Multicellular life, with their even
greater energy demands, evolved
when oxygen levels reached presentday levels.
Multicellular Life Evolved about 650 Million Years Ago
•
The first multicellular organisms—soft-bodied animals—evolved in the shallow seas that
covered the Earth during the Precambrian period, about 650 mya.
The Cambrian Period Witnessed Multiple
Adaptive Radiations of Animal Life
•
•
Starting in the early to middle Cambrian period, 530 mya, there was a dramatic increase in the diversity
of animal life, known as the Cambrian explosion, which lasted only 5–10 million years.
The presence of new predators is thought to have sped up the evolution of Cambrian herbivores.
Colonization of Land Followed the
Cambrian Explosion
•
•
•
•
Green algae were the first organisms to colonize land, about 500 mya.
Plants covered Earth by the end of the Devonian period, 360 mya.
Fungi appeared on land at about the same time as plants; the two groups developed mutualisms.
The first definite fossils of terrestrial animals are of spiders and millipedes and date from about 410 mya.
Waterproofing, Efficient Transport Mechanisms, and
Roots Helped Land Plants Acquire and Conserve Water
Land plants evolved key innovations to
deal with the challenges of terrestrial life:
- Waterproof cuticle
- Vascular systems for transport of water
and nutrients
- Structural support tissues (wood)
-Leaves and roots of various kinds
- Seeds
- Tree growth forms
- Specialized reproductive structures
Amphibians, the First Vertebrates to Colonize Land,
Are Thought to Have Descended from Lobe-Finned
Fishes
Reptiles Evolved from Amphibians and Were the First to
Evolve the Amniotic Egg, a Major Event in the History of Life
• Mammals, the dominant vertebrate group on land currently, evolved from reptiles roughly
220 mya.
The Effects of Plate Tectonics
•
•
•
•
Continents “float” on Earth’s mantle, a hot layer of semisolid rock.
The slow movement of the continents over time relative to one another is called plate
tectonics.
Plate tectonics can be caused by spreading of the sea floor or the collision and subsequent
sinking of one plate into the mantle under the other plate.
Patterns of plate tectonics have had dramatic effects on the history of life through its effects
on climate and biogeographical isolation leading to speciation.
Mass Extinctions: Worldwide Losses of Species
•
At several points in Earth’s history, the extinction rate has soared.
•
The fossil record shows that there have been five mass extinctions, periods of time during
which great numbers of species went extinct throughout most of Earth.
Each Mass Extinction Has Left a Permanent
Mark on the History of Life
Reconstruction of the
head of a Mapusaurus.
This dinosaur may have
been the largest carnivore
ever to walk the Earth.
• The mass extinctions are thought to have been caused by such
things as climate change, massive volcanic eruptions, and asteroid
impacts.
The Extinction of One or More Groups of Organisms Can Provide New
Ecological and Evolutionary Opportunities for Other Groups of Organisms
Allosaurus skeleton
Effect of mass extinctions on the diversity of life:
- First, entire groups of organisms perish, changing the history of life forever.
- Second, mass extinctions enable surviving species to experience adaptive
radiation, as the extinction of dominant groups of organisms provides new
ecological and evolutionary opportunities for groups of organisms that
previously were of relatively minor importance, dramatically altering the
course of evolution.
Rapid Macroevolution through Differential Gene
Expression
Altering how and when a
homeotic gene is expressed
in the developing embryo can
radically change the body plan
of an animal.
• Dramatic macroevolutionary changes can occur over geological timescales because of its
immense magnitude and also because geologic processes can alter the position of
continents, cause shifts in atmospheric composition, and produce large-scale extinction
events.
• However, the relatively new field of evo-devo (evolutionary developmental biology) has
demonstrated that changes in patterns of gene expression can also bring about dramatic
changes in form.
Macroevolution Does Not Necessarily Require Vast
Timescales in Order to Produce Large Changes
This legless lizard lacks legs
because a homeotic gene
for limb development is
suppressed during its
embryonic development.
• A small alteration in the expression of a single homeotic gene can
rapidly lead to a significant phenotypic change and introduce a
completely novel vertebrate body plan.
Differences in Patterns of Gene Expression Explain
Many of the Differences between Chimps and Humans
• Human and chimpanzee genomes are approximately 98 percent similar.
• Humans have the same genes for hair growth that a chimpanzee has, but these
genes are expressed only in certain areas of the body.
• The same genes responsible for facial elongation during growth are found in
both species, but they are expressed for a longer period of time in chimps than
in humans, leading to their relatively longer faces.
Atavistic Traits and Vestigial Traits Provide
Evidence That Many Existing Body Plans Are the
Product of Developmental Changes
• An atavistic trait is one that represents a reversion to an ancestral state.
• Being descended from organisms with tails, humans are sometimes born with tails
because we possess the genes for tail development within our genomes.
• Similarly, horses are occasionally born with three toes instead of one because ancestral
horses had multiple toes.
Similarities between Organisms Can Be Used to
Infer Their Evolutionary Histories
• Organizing and classifying the
tremendous diversity of life on Earth is
the focus of a discipline called taxonomy.
• Scientists classify organisms into groups
based on morphological or genetic
similarities.
• An evolutionary tree illustrates the
evolutionary history of groups of
organisms.
• The goal of phylogenetics is to construct
evolutionary trees that illustrate the
patterns of species evolution.
An Evolutionary Tree Maps the Relationship between
Ancestral Groups and Their Descendants
•
Living things have diversified
into many lines of descent, or
lineages, that have evolved into
many different types of
organisms, some of them now
extinct.
•
The node represents the most
recent common ancestor of the
two lineages in question—that
is, the most immediate ancestor
that both lineages share.
•
A given ancestor and all its
descendants make up a clade,
or branch, on an evolutionary
tree.
An evolutionary tree clusters the groups that
are most closely related on
neighboring branches.
Shared Derived Traits Are Evolutionary Novelties That
Reveal Relatedness among Species
• The most useful characteristics
for discerning evolutionary
relationships are unique features
that are found in a group’s most
recent common ancestor.
• Shared derived traits are
evolutionary novelties shared by
an ancestor and its descendants
but not seen in groups that are
not direct descendants of that
ancestor.
The Linnaean System of Biological Classification
• The Linnaean hierarchy is a system of
biological classification devised by a
Swedish naturalist named Carolus
Linnaeus.
• The species is the smallest unit (lowest
level) of classification in the Linnaean
hierarchy.
• Closely related species are grouped
together to form a genus (plural,
genera).
• Using these two categories in the
hierarchy, each type of organism is given
a unique, two-word Latin name, called
its scientific name.
In the Linnaean Hierarchy, Each Species Is Placed in Successively
Larger and More Inclusive Categories Beyond the Genus
• Closely related genera
are grouped together
into a family.
• Closely related
families are grouped
together into an
order.
• Closely related orders
are grouped together
into a class.
• Closely related classes are grouped
together into a phylum.
•
Closely related phylum are grouped
together into a kingdom.
BIOLOGY MATTERS: IS MASS EXTINCTION UNDER WAY?
• The Red List produced by the International
Union for Conservation of Nature (IUCN)
identifies the world’s threatened species. To be
defined as such, a species must face a high to
extremely high risk of extinction in the wild.
•
About 30 percent of the species evaluated by
the IUCN are threatened.
• The IUCN evaluates only about 4 percent of the
world’s 1.7 million described species.
• Some experts believe that current species loss is
approaching rates seen in some of the previous
mass extinctions.
The Iberian lynx (Lynx pardinus) is the
most critically endangered feline in the
world. About 100 individuals survive in
small populations in Spain.
Number of Species at Risk of Extinction in Some Major Groups of Organisms
NOTE: Based on the IUCN Red List, 2013.
MAMMALS
BIRDS
REPTILES
AMPHIBIANS
FISHES
MOLLUSKS
OTHER
PLANTS
TOTAL
Canada
11
16
5
1
36
5
10
2
86
United States
36
78
37
56
236
301
265
270
1,279
APPLYING WHAT WE LEARNED:
WHEN ANTARCTICA WAS GREEN
• Antarctic fossils include
Cambrian marine organisms,
land plants, birds, and
mammals, revealing that great
changes have occurred over
vast stretches of time.
• About 40 million years ago,
Antarctica broke away from the
other continental masses and
started drifting toward the
South Pole.
•
•
A circumpolar cold current contributed to the formation of the Antarctic ice cap, and the
last of the alpine flowers died out, along with nearly all other life-forms, about 14 million
years ago.
The same continental movements that brought destruction to terrestrial life in Antarctica
sowed the seeds of evolutionary diversity elsewhere.
List of Key Terms: Chapter 16
atavistic trait (p. 370)
Cambrian explosion (p. 364)
class (p. 372)
Cretaceous extinction (p. 368)
domain (p. 372)
evo-devo (p. 369)
family (p. 372)
genus (p. 372)
geologic time (p. 359)
homeotic gene (p. 369)
kingdom (p. 372)
lineage (p. 371)
Linnaean hierarchy (p. 372)
macroevolution (p. 359)
mantle (p. 365)
mass extinction (p. 366)
most recent common ancestor (p. 371)
node (p. 371)
order (p. 372)
Permian extinction (p. 366)
phylogenetics (p. 371)
phylum (p. 372)
plate tectonics (p. 365)
radioisotope (p. 359)
scientific name (p. 372)
shared derived trait (p. 372)
species (p. 372)
supercontinent (p. 365)
taxon (p. 373)
taxonomy (p. 371)
The coelocanth, a living fossil
Class Quiz, Part 1
What was the first significant source of the
oxygen that began to accumulate in Earth’s
atmosphere?
A. Anaerobic bacteria
B. Photosynthesizing prokaryotes
C. Minerals in Earth’s mantle
D. Land plants
Class Quiz, Part 2
Which of the following were present on
Earth 3.0 billion years ago?
A.
B.
C.
D.
Prokaryotes
Eukaryotes
Multicellular organisms
Mammals
Class
Quiz,
Part 3
We can infer from this evolutionary tree that
A. black bears do not belong on the clade that includes the walrus, the elephant
seal, and the giant panda.
B. walruses are the most advanced among these mammals.
C. the most recent common ancestor of the gray wolf and domestic dogs
evolved more recently than the most recent common ancestor of the coyote
and the gray wolf.
Class Quiz, Part 4
The figure shows the Linnaean
hierarchy for the Chinese rose,
Rosa chinensis. Which of the
statements that follow is
true?
A. The genus that this rose belongs to
is “chinensis.”
B. All roses belong to the genus Rosaceae.
C. The order in which roses are placed is “Rosa.”
D. The order in which roses are placed is “Rosales.”
The Linnaean Hierarchy for Rosa
Chinensis
Relevant Art from Other
Chapters
All art files from the book are available in
JPEG and PPT formats online
Milestones in the History
of Life on Earth, Part 1
Milestones in the History of Life on
Earth, Part 2
Milestones in the History of Life on
Earth, Part 3
16.1 Concept Check, Part 1
1. What is macroevolution?
ANSWER: Macroevolution is large-scale evolution in
which the effect of natural selection is seen as radical
changes in body plan, not simply a change in allele
frequencies.
16.1 Concept Check, Part 2
2. Why is the concept of geologic time so
important to our understanding of
macroevolution?
ANSWER: A short timescale would make it difficult to
argue convincingly that natural selection could shape
the entire biodiversity seen on Earth.
16.2 Concept Check, Part 1
1. What is a fossil?
ANSWER: A fossil is the preserved traces of an
organism. Fossils may include petrified bone,
impressions cast in stone, or any other remnant of a
once-living organism.
16.2 Concept Check, Part 2
2. Why is the fossil record so incomplete?
ANSWER: The conditions for fossil preservation are
relatively rare. Some organisms are more likely to be
fossilized than others (for example, bony versus softbodied animals).
16.3 Concept Check, Part 1
1. Why was it significant that early bacteria
evolved the ability to carry out
photosynthesis?
ANSWER: Oxygen is a by-product of photosynthesis,
and increasing oxygen in the atmosphere set the stage
for the evolution of eukaryotes, a group that includes all
multicellular life.
16.3 Concept Check, Part 2
2. How did the Cambrian explosion change life
on Earth?
ANSWER: The Cambrian explosion marks the
appearance of most of the major living animal phyla,
many of which were the world’s first predators.
16.4 Concept Check, Part 1
1. Why is the age of Earth a key factor in
discussions of plate tectonics?
ANSWER: Because the continents move so slowly, the
effects of plate tectonics are apparent only over long
timescales
16.4 Concept Check, Part 2
2. What are two ways that plate tectonics can
affect biodiversity?
ANSWER: The movement of continents can
geographically isolate populations, leading to allopatric
speciation (see Section 15.2). It can also alter climate
by changing ocean currents.
16.5 Concept Check, Part 1
1. Given the long history of Earth, why have so
few mass extinctions been recorded?
ANSWER: The causes of mass extinctions are global in
scale and catastrophic in magnitude. Such events are
inherently rare.
16.5 Concept Check, Part 2
2. What is the impact of mass extinction
events on biodiversity?
ANSWER: Many species are lost in mass extinction
events, but their loss opens up ecological niches
permitting the adaptive radiation of successor species.
16.6 Concept Check, Part 1
1. What is a homeotic gene?
ANSWER: A homeotic gene controls the embryological
development of a body structure.
16.6 Concept Check, Part 2
2. Explain why the discovery of homeotic
genes had a significant impact on evolutionary
thought.
ANSWER: Prior to the discovery of homeotic genes,
macroevolutionary change was thought to occur solely
over long periods of time. Changes in homeotic gene
expression, however, have shown that significant
alterations in body plans can occur in a single
generation.
16.7 Concept Check, Part 1
1. In evolutionary terms, what happens at a
node?
ANSWER: A node represents a speciation event in
which one lineage splits into two.
16.7 Concept Check, Part 2
2. List the eight taxonomic tiers of Linnaean
classification, beginning with the most
inclusive.
ANSWER: Domain, kingdom, phylum, class, order,
family, genus, species