CHAPTERS 15-17: EVOLUTION,
NATURAL SELECTION, AND THE
FOSSIL RECORD
EVOLUTION: the process by which
modern organisms have descended from
ancient organisms
Biological diversity: the variety of living
things found in a given area
Theory: well – supported testable explanation
of phenomena that have occurred in the
natural world
Charles Darwin
A naturalist who joined the
crew of the HMS Beagle and
sailed around the world made
numerous observations and
collected evidence that led
him to propose a revolutionary
hypothesis about the way life
changes over time.
Observations made by Darwin
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Enormous number of species inhabit the
Earth
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Many plants and animals well suited to their
environments
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Many different methods of reproduction
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Different organisms inhabit similar habitats
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Some fossils resemble living organism
whereas other fossils do not
Galapagos Islands

Small islands located 1000km west of
South America that influenced Darwin
the most
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Islands close together with very
different climates
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Characteristics of many animals and
plants varied noticeably among the
different islands

The shells of giant tortoises
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The beaks of different birds

What hypothesis did Darwin
form concerning the biological
diversity of the Galapagos
Islands?
The animals living on the
different islands had once been
members of the same species.
Ideas that shaped Darwin’s thinking
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James Hutton  Geologic Change
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geologic process and change occur very slowly
the Earth is much older than previously thought
Charles Lyell  Principles of Geology
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The geologic processes that affect the earth today
are the same that affected the earth in the ancient
past
Uniformitarianism: “The present is the key to the
past”
Earthquakes, volcanoes, erosion
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Jean – Baptiste Lamarck
 Evolution Hypothesis
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Recognize that living things
change over time
All species were descended from
other species
Organisms adapted to their environments
By selective use or disuse of organs,
organisms acquired or lost certain traits
during their lifetime.
 These traits then could be passed on to
their offspring.
 Over time, this process led to changes
in a species.
Summary of Lamarck's Ideas
a.) Tendency Toward Perfection
 proposed that all organisms have an innate tendency toward
complexity and perfection
 continually changing and acquiring features that help them live
more successfully in their environments
b.) Use and Disuse
 proposed that organisms could alter the size or shape of
particular organs by using their bodies in new ways
c.) Inheritance of Acquired Traits
 thought that acquired characteristics could be inherited
d.) Evaluating Lamarck’s Hypothesis
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INCORRECT Traits are inherited
Behavior has no effect on its heritable characteristics
First to develop a scientific hypothesis of evolution
Realized organisms are adapted to their environments
Thomas Malthus  Population Growth
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English economist
Reasoned if the human population
continued to grow unchecked, sooner
or later there would be insufficient living
space and food for everyone
Implications on Darwin’s ideas
 Applied even more strongly to
plants and animals
 Does not happen due to high
mortality rate of offspring
 Of those that reach adulthood
only a small portion reproduce
What was
the name of the
publication
of
Darwin’s research?

What did Darwin propose as a
mechanism for evolution in his
publication?
Natural Selection
What do plant and animal breeders use to
improve crops and livestock?
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Inheritable or genetic variation
Darwin termed this process artificial
selection
a.) Artificial selection: The process in which nature provides
variation and humans select the
variations they find useful
What is natural selection?
The process where nature provides both
the genetic variation and selective
processes to bring about speciation
Struggle for Existence
The members of one species compete regularly
to obtain food, living space, and other necessities
of life
Central to Darwin’s theory of evolution

Fitness

the ability of an individual to survive and reproduce in
its specific environment
 fitness is a result of adaptation

Adaptation

any inherited
characteristic that
increases an
organism’s chance
of survival
 anatomical,
structural,
behavioral,
physiological
Survival of the Fittest
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Key factor in the struggle for existence
Also called NATURAL SELECTION
 successful adaptations enable organism to become better suited
to their environments and thus better able to survive and
reproduce

Over time, natural selection…
 results in changes in the
inherited characteristics of a
population
NATURAL SELECTION…

CANNOT BE SEEN DIRECTLY IT CAN ONLY BE
OBSERVED AS CHANGES IN A POPULATION OVER
MANY SUCCESSIVE GENERATIONS
The Principle of Descent With
Modification

the principle that each living species
has descended, with changes, from
other species over time
a.) Darwin proposed that over long periods,
natural selection produces organisms that
have different structures, establish different
niches, or occupy different habitats
b.) Descent with modification also implies…
that all living organisms are related to one
another
The Principle of Common Descent
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all species (living and extinct) were
derived from common ancestors
Evidence of Evolution
a.) The Fossil Record

fossils are the remains of ancient life

by comparing fossils from older rock layers with fossils from
younger rock layers, scientist could document the changes in
life over time

discovery of transitional species document various
intermediate stages in the evolution of modern species from
organisms that are now extinct

gaps remain in the fossil record point out uncertainties in our
understanding of exactly how some species evolved
b.) Geographic Distribution of Living Species
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different species similar in appearance living on
different continents descended from different
ancestors
the similarity in appearance is due to the similar
selection pressures under which the organisms were
exposed
the similar natural selective pressures
existed because the ecological conditions were
similar
c.) Homologous Body Structures
Homologous structures are structures
that have different mature forms but
develop from the same embryonic
tissues
1.)
wings, fins, arms provide strong evidence that all four limbed
vertebrates have descended, with modifications, from common
ancestors
the similarities and differences help biologist group animals
according to how recently they last shared a common ancestor
2.) Vestigial Organs
organs that serve no useful function In an organism
 homologous structures: appendix, coccyx,
whale hind legs
d.) Similarities in Embryology

similarities of embryonic animals with backbones
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same group of embryonic cells develop in the same
order and in similar patterns to produce the tissues
and organs of all vertebrates  produce
homologous
structures
Summary of Darwin’s Theory
a.) Individual organisms differ, and…
some of this variation is heritable
b.) Organisms produce more offspring
than can survive, and many that do
survive do not reproduce
c.) Because more organisms are
produced than can survive, they
compete for limited resources
d.) Each unique organism has different
advantages and disadvantages in the
struggle for existence
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individuals best suited to their environment survive
and reproduce most successfully
these organisms pass their heritable traits to their
offspring
other individuals die or leave fewer offspring
this process of natural selection causes
species to change over time
e.) Species alive today…
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are descended with modification from ancestral
species that lived in the past
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this process, by which diverse species evolved from
common ancestors, unites all organisms on Earth
into a single tree of life
Strengths and Weaknesses of
Evolutionary Theory
a.) Strengths
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scientific advances in many fields of biology and
physics have confirmed and expanded most of
Darwin’s hypotheses
evolutionary theory offers vital insights to all
biological and biomedical sciences
evolution is the grand unifying theory of the life
sciences
b.) Weaknesses
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continues to change as new data are gathered and
new ways of thinking arise
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limited fossil record
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uncertainties of how new species arise and how
species become extinct
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uncertainty about how life began
THE PROCESS OF SPECIATION
1. Speciation is the formation of a new species.
2. Factors such as natural selection and chance
events can change the relative frequencies of
alleles in a population.
3. The gene pools of two populations must become
separated for them to become new species.
4. As new species evolve, populations become
reproductively isolated from one another.
5. Reproductive isolation has occurred when
members of two populations cannot interbreed
and produce fertile offspring
Mechanisms of Reproductive Isolation
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Behavioral isolation
Occurs when two populations are capable of interbreeding but have differences in
courtship rituals or other reproductive strategies that involve behavior
 Example: Eastern and Western Meadowlarks  use different songs to attract
mates
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Geographic isolation
Occurs when two populations are separated by geographic barriers such as rivers,
mountains, or bodies of water
 Example: Albert and Kaibab squirrels  separated by the Grand Canyon, with
the Kaibab squirrel on the North Rim and the Albert squirrel on the
South Rim
Geographic barriers do not guarantee the formation of a new species
 birds can fly over rivers
 periodic droughts in lake areas create land bridges
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Temporal isolation
Occurs when two or more species reproduce at different times
 Example: 3 similar species of orchid all live in the same rain forest
 Each species releases pollen only on a single day
 Since each species releases pollen on different days, they cannot pollinate one
another
FOSSIL RECORD
Fossils and Ancient Life
Paleontologists are scientists who collect and study fossils.
 They infer what past life forms were like and how they lived
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They group similar organisms together and arrange them in the
order in which they lived; from oldest to most recent.
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Together, all this information about past life is called the fossil
record.
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The fossil record provides
evidence about the history
of life on Earth.
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It also shows how different
groups of organisms,
including species, have
changed over time.
FOSSIL RECORD
The fossil record reveals a remarkable fact:
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Fossils occur in a particular order.
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Certain fossils appear only in older
rocks, and other fossils appear only
in more recent rocks.
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In other words, the fossil record
shows that life on Earth has changed
over time.
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In fact, more than 99 percent of all
species that have ever lived on Earth
have become extinct, which means
the species died out.
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Meanwhile, over billions of years, ancient unicellular organisms
have given rise to the modern bacteria, protists, fungi, plants,
and animals.
FOSSIL RECORD
Interpreting Fossil Evidence
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When a fossil is exposed, apaleontologist may happenalong at just the right
time and remove the fossil for
study.
Paleontologists occasionally
unearth the remains of an entire
organism.
More often, though, they must
reconstruct an extinct species from
a few fossil bits—remains of bone,
a shell, leaves, or pollen.
When paleontologists study a
fossil, they look for anatomical similarities—and differences—between the
fossil and living organisms.
Also, a fossil's age is extremely important.
Paleontologists determine the age of fossils using two techniques: relative
dating and absolute dating.
FOSSIL RECORD
Relative Dating of Fossils
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Relative dating: the age of a fossil is determined by comparing its
placement with that of fossils in other layers of rock.
Scientists also use index fossils to compare the relative ages of
fossils.
To be used as an index fossil, a species must be…
1. widespread
3. recognizable
2. abundant
4. short lived
FOSSIL RECORD
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As a result, it will be found in only a few layers of rock, but these
specific layers will be found in different geographic locations.
Relative dating allows paleontologists to estimate a fossil's age
compared with that of other fossils. However, it provides no
information about its absolute age, or age in years.
FOSSIL RECORD
Absolute dating of Fossils
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Absolute dating involves the use of radioactive isotopes to
identify the age of a fossil in years.
Radiometric dating involves measuring the amounts of
radioactive isotopes in a
sample to determine its
actual age.
Such measurements
enable scientists to
determine the absolute
age of rocks and the fossils they contain.
Isotopes of uranium,
carbon and potassium
are used to absolutely
date a fossil.
GEOLOGIC TIME LINE