Transcript chapter 7 modx

Chapter
7
Darwinian Evolution
Lecture Presentation
by Wendy Kuntz
© 2015 Pearson Education, Inc.
Chapter 7 Darwinian Evolution:
Unit Hyperlinks
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7.1 Darwin’s influences
7.2 Natural selection
7.3 Fossil record
7.4 Evidence for evolution
7.5 Populations are the units
7.6 Evolutionary mechanisms
7.7 Macroevolution
7.8 Geological record
7.9 Reproductive barriers
7.10 Speciation
7.11 Taxonomy
7.12 Phylogenetic trees
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7.1 Opening Questions: How to explain the
unity and diversity of living things?
• The Earth is filled with a wide diversity of
organisms.
List at least three examples of how living
things can differ.
• Yet there is also great unity among living
things
List at least three traits or processes that
all living things have in common.
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7.1 November 24, 1859, is a landmark date
in the history of biology
• In 1859, British naturalist
Charles Darwin published
On the Origin of Species
by Means of Natural
Selection.
• In the Origin of Species
Darwin introduced the
concepts of evolution
and natural selection.
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7.1 Until the 1800s most scientists had a
different view of life and species
• In early history, most
thought a young Earth
held unrelated and
unchanging species.
• The discovery of fossils
(1700s) first suggested
that the Earth was very
old and that species
could change over time.
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Aristotle believed
species were immutable.
Darwinius
masillae
fossil
7.1 By the 1800s new views about species
and the history of Earth had emerged
• Jean Batiste de Lamarck, a
French biologist was one of
the first to suggest that
species change over time
(evolution).
• Charles Lyell, an English
geologist and friend of
Charles Darwin suggested
that an old Earth had
gradually changed through
slow, accumulating
processes.
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7.1 Darwin’s influences and experiences
led him to his theory of evolution
• As a youth, Darwin spent
time observing nature.
– He first studied beatles
– After graduated from
college, he travels
around the world on the
HMS Beagle (18311836)
• Darwin's travels allowed
him to compare species
from different regions.
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The voyage of the Beagle:
1831–1836
7.1 Darwin began an in-depth study of
change over time (evolution)
• Darwin spent decades
reading, analyzing his
specimens, and discussing
ideas with colleagues.
• Darwin was the first to
propose a mechanism to
explain how species could
evolve: natural selection.
Darwin’s beetle collection
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7.2 Opening Questions: Observations on
the natural world: True or false?
If the answer is false, explain why:
• True or false: Populations tend to be
stable in size.
• True or false: Resources are unlimited.
• True or false: All individuals of a
particular species in a population are
exactly alike.
• True or false: Traits can be inherited.
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7.2 In The Origin of Species Darwin made
two important points
• First, modern species have
descended from common
ancestors (evolution).
• Second, natural selection is
the mechanism of evolution.
Darwin arrived at the idea of evolution by
natural selection through several
important observations and conclusions.
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7.2 Darwin first observed that populations
produce more individuals than can survive
• Observation: Overproduction
– More individuals are born
than can be supported by
the environment.
• Observation: Limited resources
– The amount of resources
(such as food, water,
shelter, sunlight) stays
relatively constant.
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7.2 Darwin concluded that competition was
a factor for all living things
• Conclusion: Competition
– More offspring are born than
can be supported by limited
resources; not all individuals
survive and reproduce.
(differential reproductive
success)
• Observation: Variation
– Darwin also observed that
no two individuals are alike.
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7.2 Darwin concluded that favorable
variations will be naturally selected
• Conclusion: Natural selection
– Those individuals with variations that make
them best suited to their environment will,
on average, be more
likely to survive and
reproduce.
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7.2 Darwin concluded that natural selection
can lead to evolution
• Observation: Heritability
– The traits of an organism
are likely to be passed to
the next generation.
• Conclusion: Evolution
– Because traits are passed from one
generation to the next, and because certain
members are more likely to survive and
reproduce, a population will change over time,
becoming better suited to its environment.
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7.2 Important points about evolution
• Individuals don’t evolve.
– Natural selection acts on
individuals, but only
populations evolve.
• Natural selection works
with heritable traits.
– Only genetically coded traits are subject to
natural selection.
• Evolution does not have a goal.
– Evolution occurs in response to local
environmental conditions, not future ones.
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7.3 Opening Questions: How are Darwin’s
observations and conclusions connected?
• Replicate the figure below on a full page in your
notes. Identify Darwin’s observations and
conclusions. Draw connections between the ideas.
For each connecting line write an explanation.
Limited
resources
Overproduction
Competition
Natural
selection
Variation
Heritability
Evolution
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7.3 The fossil record provides important
evidence for evolution
• Fossils form when organisms die, fall into
accumulating sediment, and are
compressed into rock.
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7.3 Fossils provide a glimpse into the past
• Fossils can be dated using
their geological position
and/or through radiometric
dating.
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7.3 Carbon 14
•
•
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•
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Carbon 14 nitrogen 14
for specimens younger than
50,000 years
The half life of C14 is about
5600 years
So if a sample has 1/2 of
the original sample, than
the sample is 5600 years
old
If only ¼ of the original
sample is present, than 2
half-lives have passed so
the sample is 11,200 years
old
An approximations can be
determined by this
age of fossil= ½ life x
number of half life's
passed
So if one multiply by 2 if ¼
of the sample is left, if 12.5
% is left than that would be
3 half life’s
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Radiometric dating
• Is the most common method for dating fossils.
• Has helped establish the geologic time scale.
• Different isotopes have different ½ life's
• For example C14 has a half- life of about 5600 years
• Radiometric dating method relies on radioactive dating
techniques.
– All radioactive isotopes have a particular half-life.
• Length of time it takes for half of the radioactive isotope to change into
another stable elements
•
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•
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– Compare radioactivity of a fossil to that of a modern sample of organic
matter.
Radiometric dating involves measuring content of radioactive
isotopes such as
Carbon 14 nitrogen 14 for specimens younger than 50,000 years
K40argon 40 for specimens that are million years old such as
dinosaur bones
Rb87St87 for Paleozoic rocks
• Decay of uranium can also be used. Its half life is
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7.3 How does the fossil record provide
evidence of evolution?
• The fossil record reveals an ordered
appearance of life on Earth, from
prokaryotes to today’s life forms.
• Transitional forms provide evidence of
change within lineages.
Fossil whales with rear
legs are examples of
transitional forms.
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7.4 Opening Questions: Can we predict
evolution?
Write a short answer to the question below:
• What characteristics must be present in
a population and the environment in
order for natural selection to occur in a
population?
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7.4 The geographic distribution of species
provides much evidence of evolution
• Biogeography is the study
of the geographic
distribution of species.
• For example, the geographic
isolation of Australia
accounts for the dominance
of marsupial mammals.
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7.4 The geographic distribution of species
provides much evidence of evolution
• A. Wallace and Biogeography
– On the Tendency of Varieties to Depart
Indefinitely From the Original Type
• Alfred Wallace also came up with natural
selection after his journey around the
world as a mechanism by which
populations evolve
• He studied the affects of geography on the
biological distribution and diversity Biogeography
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7.4 Comparative anatomy provides much
evidence of evolution
• Comparisons of the body structures of
modern organisms is called comparative
anatomy.
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7.4 Comparative anatomy can provide
insight into evolutionary history
• Examination of animal forelimbs shows they
are all constructed from similar bones.
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7.4 DNA and bioinformatics provide much
evidence of evolution
• All life uses DNA
for genetic code.
• Closely related
species will have
similar DNA and
protein sequences.
– Such as in primates
• Bioinformatics employs computational
tools to process genetic data.
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7.5 Opening Questions: What exactly is a
population?
• Populations are the smallest unit that can
evolve. But what is a population?
Answer the following questions:
1. How would you define a population?
• Is your class a population?
• Is your country a population?
• Is the entire human species a population?
2. How might biologists define a
population? Explain.
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7.5 Populations are the units of evolution
• Natural selection
acts on individuals.
• However, evolution
is defined only in
terms of changes in
a population over
time.
A population is a group of individuals of the
same species living in the same place at the
same time.
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7.5 Members of a population are capable
of meeting and mating
Birds: Same
population
Fish: Same
population
Squirrels:
Different
population
Squirrels
don’t swim!
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7.5 The members of a population may carry
different gene versions
• The gene pool consists
of all versions of all the
genes carried by all the
individuals in a population.
• Genetic variation in a
gene pool can arise
through mutation.
• Sexual reproduction
ensures that genes are
randomly mixed.
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7.5 Natural selection acts on the gene pool
• Traits that enhance
survival and reproduction
will be represented with
increasing frequency in
the gene pool.
• A generation-to-generation change in the
gene pool is called microevolution, which
is evolution occurring on its smallest scale.
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7.5 Microevolution is a generation-togeneration change in the gene pool
Taken over many generations, microevolution
can result in the gradual adaptation of species
to the local environment.
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7.6 Opening Questions: Can you breed a
Chihuahua?
• Imagine you have a pack of wolves.
• How could you turn your wolves into
Chihuahuas?
• Explain why your strategy would work.
Extra thought
question: Is body
size the only trait
that matters?
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7.6 Changes to the genetic makeup of a
population can arise via two mechanisms
1. Mutations: Random
changes to DNA which
can create new genes.
2. Sexual recombination:
During the formation of
sperm and eggs,
chromosomes can
exchange pieces of
DNA, shuffling genes.
Crossing over
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7.6 Natural selection and fitness
• Darwinian fitness is the contribution that
an individual makes to the gene pool of the
next generation in comparison to the
contributions from other individuals.
• The fittest individual is
not always the strongest.
There are many sorts
of adaptations that
can improve fitness.
Camouflage is an adaptive trait.
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7.6 Mechanisms of evolution
What can lead to
changes in a gene
pool over successive
generations?
Hint: We’ve already discussed one important
mechanism that can result in gene pool change.
Natural selection is the primary mechanism
that can lead to a change in a gene pool,
also known as evolution.
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7.6 Mechanisms of evolution
• In addition to natural selection, there are
other mechanisms that can also contribute
to evolution in gene pools.
– Genetic drift
– Bottleneck and founder effect
– Gene flow
– Sexual selection
In evolving populations,
some combination of all
the mechanisms operates.
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7.6 Genetic drift can lead to changes in a
gene pool over successive generations
• Genetic drift is a change in a gene pool
due to chance.
– For example, genes may be lost if a few
individuals die or migrate at random.
– This is important in small, or isolated,
populations.
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7.6 The bottleneck and founder effects can
change gene pools
• If a population is drastically reduced in
numbers, that is a bottleneck.
• If a few individuals migrate to a new
isolated habitat, that is a founder effect.
• In either case, by chance,
some genes will be lost
from the gene pool.
In the 1800s, cheetah
numbers were
drastically reduced.
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7.6 Gene flow tends to reduce differences
among gene pools
• Most populations are not isolated.
• Gene flow is the genetic exchange among
populations due to migration.
Drifting pollen may transfer
genes between distant
populations, causing them
to become more genetically
similar over time.
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7.6 Sexual selection can lead to changes in
a gene pool over successive generations
• Sexual selection is a form of natural
selection that depends on an individual’s
ability to obtain a mate.
• Females may choose
males for their traits.
• Males may compete
with each other for
access to mates.
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7.6 Review Questions: Survival of the
prettiest?
• While working on his
theory of natural
selection, Darwin was
quite troubled about
peacocks.
• A long tail makes them
vulnerable to predators.
Why might a peacock, with its long, beautiful
tail, initially have troubled Darwin?
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7.7 Opening Questions: Do only the strong
survive?
Do you agree or disagree with the following
statement? Explain your answer.
Only the strongest individuals in a
population will survive to reproduce.
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7.7 Macroevolution encompasses the major
changes in the history of life
• Macroevolution is
genetic change on a
large scale.
• Speciation is the
evolutionary formation
of new species.
Earth’s incredible diversity represents a long
history of evolution, as ancestral species gave
rise to one or more new species.
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7.7 Speciation may occur through two
different mechanisms
• In nonbranching
evolution, an
ancestral population
changes gradually.
• In branching
evolution, an
ancestral population
splits into two or
more populations.
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7.7 Novel features may spur large-scale
evolution
• Throughout the history of life on Earth,
novel features have evolved.
• The evolution of
feathers and flight in
birds is an example of
how structures that
serve one role can
gradually change to
serve another.
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7.7 Rapid species diversification follows
mass extinctions
• There have been five
mass extinctions in the
history of life.
• Following the mass
extinction of the
dinosaurs 65 mya,
mammals diversified.
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7.8 Opening Questions: Can you trust
Fred Flintstone?
• Did any of our human
ancestors ever ride a
dinosaur to work?
• Did they ever fry up a
dinosaur egg for breakfast?
• Or have a cute little “dino”
for a pet?
As fun as it is to imagine, what is wrong with
the above scenarios? Explain.
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7.8 The geological record ties together
the history of Earth and its life
• Geologists recognize four broad eras in
the history of Earth, each marked by the
appearance of distinctive life.
• Each era represents a distinct period in the
history of life.
Precambrian
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Paleozoic
Mesozoic
Cenozoic
7.8 Precambrian era: 4.6 bya to 541 mya
Highlights from the Precambrian:
• 4.6 bya: Earth forms
• 3.5 bya: Oldest known prokaryote
(primitive-celled) fossils
• 2.1 bya: Oldest known eukaryote
(modern-celled) fossils
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7.8 Paleozoic era: 541 to 251 mya
Highlights from the Paleozoic:
• 541 mya: Explosion in animal diversity
within the oceans
• 420 mya: Plant life begins on land
• 370 mya: Animals migrate to land
• 251 mya: Mass extinction event
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7.8 Mesozoic era: 251 to 65 mya
Highlights from the Mesozoic:
• 230 mya: First dinosaurs
• 100 mya: Flowering plants begin to
dominate the land
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7.8 Cenozoic era: 65 mya to today
Highlights from the Cenozoic:
• 65 mya: Extinction of dinosaurs and
diversification of mammals
• 200,000 years ago: Appearance of
anatomically modern humans
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7.8 Earth’s geology has had a profound
impact on the history of life
• The Earth’s crust is composed of large
tectonic plates floating atop a very hot
layer of rock called the mantle.
• Plate movement continuously rearranges
the geography of the continents.
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7.8 The Earth is a dynamic planet
• Geological upheavals can be catastrophic
in the short term and can alter the
evolution of life on Earth in the long term.
– Earthquakes, mountain building, volcanoes
Changes in the
Earth’s geology
over time have
intertwined with
the history of life
on Earth.
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7.9 Opening Questions: Lions and tigers!
Oh, my!
• Imagine you are visiting the zoo, and in
the Big Cats exhibit you see lions from
Africa and tigers from Asia.
• We consider lions and tigers different
species. Why?
In captivity, mating between lions and tigers
may lead to hybrid “ligers.” Are “ligers” a
species? Why or why not?
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7.9 What is a species?
• The word “species” is derived from a Latin
word meaning “appearance.”
• However, appearance alone cannot be
used to tell one species from another.
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7.9 What is a species?
• The most commonly
used definition of
species is a
population that is
capable of
interbreeding to
produce healthy,
fertile offspring.
What types of species might not fit the
definition above?
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7.9 What is a species?
• Our earlier definition focused
on interbreeding doesn’t work
for all species.
– Bacteria reproduce asexually.
– For extinct organisms, we can’t
know if they were capable of
mating.
• For some organisms, we have
to use appearance, or another
means, to determine species groups.
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7.9 Reproductive barriers maintain species
• For species that we can define as a group
of individuals capable of successfully
interbreeding, what keeps them separate?
• One or more reproductive barriers
prevent members of different species from
breeding.
What might prevent
Eastern and Western
meadowlarks from
interbreeding?
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7.9 Reproductive barriers maintain species
• Behavioral isolation:
Members of a species often
identify each other through
specific rituals.
• Mating time differences:
Many species are able to
reproduce only at specific
times.
• Habitat isolation:
If species live in slightly
different habitats, they may
never meet.
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7.9 Reproductive barriers maintain species
• Mechanical incompatibility:
Members of different species
often cannot mate because their
anatomies are incompatible.
• Gametic incompatibility:
The gametes (sperm and egg
of different species usually
cannot fertilize each other.
• Hybrid weakness:
Offspring of two species
may be unfit, or they may
be sterile.
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7.9 Review Questions: Lions and tigers!
Oh, my!
Lions and tigers can produce a hybrid
“liger” offspring.
Does this mean that lions and tigers
are the same species? Explain.
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7.10 Opening Questions: How do we get
new species?
• Imagine that a small flock of forest
birds gets blown off course during a
hurricane. The flock lands on a
small, dry, and grassy island. You
locate this population 300,000 years
later.
• Do the current birds look the same or different
from the original colonists? Draw pictures of
your imagined birds.
• Do they have the same behaviors?
• Would you consider them the same species
or different from the original species? Explain.
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7.10 How do we get new species?
• Speciation occurs when
one ancestral species
evolves into one or more
new species.
• Some event separates a
population:
– Time, space, or genetics
Species
A
Species
B
Original
Population
• Populations then diverge along their own
evolutionary path.
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7.10 New species may form over long
periods of time
• In the graduated model, a species
acquires small adaptations to its
environment over millions of years.
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7.10 New species may form relatively rapidly
• In the punctuated equilibrium model,
there are periods of stasis interrupted by
occasional bursts of speciation.
530 million years ago during
a period called the Cambrian
explosion, the rate of
evolution was an order of
magnitude higher than the
normal rate. (It still required
millions of years.)
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7.10 New species may form after geographic
isolation
• Allopatric speciation may occur when a
physical barrier isolates populations.
The formation of the
Grand Canyon produced
two isolated habitats.
One species of squirrel is
now found exclusively on
each side of the canyon.
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7.10 New species may form within a parent
species
• Sympatric speciation may occur quite
suddenly due to large-scale genetic
changes. (There is no physical barrier.)
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7.11 Opening Questions: What do we know
about evolution anyway?
Write a short response to the following question:
• What are at least three things you know
that provide supporting evidence for
evolution?
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7.11 Taxonomy is the classification of life
• Taxonomy is the identification, naming,
and classification of species.
• All life is classified into one of three large
groups called domains based on cell type.
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7.11 Where does a tiger fit in the taxonomic
hierarchy?
• Starting with a domain,
every organism can be
placed into the
taxonomic hierarchy,
an ordered series of
progressively smaller
categories.
• The hierarchy ends
with the species name.
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Panthera tigris
7.11 Where does a tiger fit in the taxonomic
hierarchy?
•
•
•
•
•
•
•
•
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
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7.11 Where does a tiger fit in the taxonomic
hierarchy?
• Species are identified using the last two
groups in the hierarchy: Genus species.
• This binomial (two-part) is sometimes
called a “scientific name.”
Panthera tigris
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7.12 Opening Questions: How can we map
our ancestry?
• Sketch out a quick family lineage for your
immediate family.
– How far back can you go? Your grandparents?
Great-grandparents? Great-great-grandparents?
What shape best describes your family sketch?
Explain.
• We often refer to our “family tree” when
discussing our ancestry.
Why might trees be a useful term to represent
relationships?
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7.12 Evolutionary relationships may be
represented by branching trees
• Phylogenetic trees
are one way to reflect
the evolutionary
history of organisms.
• Phylogenetic trees
present a hypothesis
about the evolutionary
history of related
species.
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Species
A
Species
B
Species
C
EVOLUTION:
BIOLOGY’S UNIFYING THEME
– Life evolves.
•
•
Each species is one twig
of a branching tree of life
extending back in time
through ancestral species
more and more remote.
Species that are very
similar, such as the brown
bear and polar bear,
share a more recent
common ancestor.
– Reading the table:
•
•
10 million years ago how
many species of bear
existed (answer: 2)
Presently how many
species of bear exist?
–
•
Answer: 8
Of the bears that exist
today which two are most
closely related?
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Pearson
Education,
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Pearson
Education,
Inc. Inc.
phylogeny n : the sequence of events involved in the
evolutionary development of a species or taxonomic group of
organisms
7.12 Bear
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• The Polar bear
and the Brown
bear are closely
related
– They share so
many genes
they are able
to form
hybrids
• Which two bears
species are most
closely related
after these two?
7.12 Clades can be thought of representing
a branch on the tree of life
• A clade is a any group of species that
consists of an ancestral species and all its
descendants.
• The analysis of clades is called cladistics.
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7.12 Reading phylogenetic trees can provide
insights into the interrelationships of life
• The tips of the tree
represent groups of
the most recently
evolved species.
• To determine how
closely related two
species are, find their
most recent common
ancestor.
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Species
A
Species
B
Species
C