Transcript Unit7PP

Unit 7 Big Idea
Evolution provides a scientific explanation for
the history of life on Earth.
Unit 7 Core Concepts
The millions of different species of plants, animals, and
micro-organisms that live on Earth today are related by
descent from common ancestors.
Evolution of species is, in part, the result of the
process of natural selection.
Genetic variation is preserved or eliminated from a
population through the process of natural selection.
Before we begin...
Isn't evolution JUST a theory?
Theory in science?
Theory in everyday language?
Click here for an explanation!
Biological evolution is not simply a matter of change over
time. Lots of things change over time: trees lose their
leaves, mountain ranges rise and erode, but they aren't
examples of biological evolution because they don't
involve descent through genetic inheritance.
The central idea of biological evolution is that all
life on Earth shares a common ancestor, just as
you and your cousins share a common
grandmother.
Through the process of descent with
modification, the common ancestor of life on
Earth gave rise to the fantastic diversity that we
see documented in the fossil record and around
us today. Evolution means that we're all distant
cousins: humans and oak trees, hummingbirds
and whales.
Evolution – A brief overview
Fill in the table in your notes. Use what you
learned from the video “What Darwin Didn’t Know”
that we have watched the past two days.
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B5.2a Describe species as reproductively
distinct groups of organisms that can be
classified based on morphological, behavioral,
and molecular structures.
B2.4A Explain that living things can be
classified based on structural, embryological,
and molecular (relatedness of DNA sequence)
evidence.
B5.2b Explain that the degree of kinship
between organisms or species can be
estimated from similarity of their DNA and
protein sequences.
Charles Darwin & the HMS Beagle
If you’d met young Charles Darwin, you
probably wouldn’t have guessed that his
ideas would change the way we look at the
world. As a boy, Darwin wasn’t a star
student. Yet Charles would one day come up
with one of the most important scientific
theories of all time!
Fun Fact: Charles Darwin was born
in England on February 12, 1809.
The same day as Abraham Lincoln!
Darwin’s Epic Journey
Charles Darwin grew up at a time when the scientific view of the
natural world was shifting dramatically.
Geologists were suggesting that Earth was ancient and had changed
over time, and biologists were suggesting that life on Earth had also
changed.
Descent through genetic inheritance is called evolution.
As Darwin sailed and made observations, he developed a scientific
theory of biological evolution that explains how modern organisms
evolved over long periods of time through descent from common
ancestors.
Sound familiar?? Check your Unit 7 Core Concepts!
Darwin’s Epic Journey
Darwin was invited to sail on the HMS Beagle’s five-year
voyage mapping the coastline of South America. Darwin
planned to collect specimens of plants and animals on the
voyage. No one knew it at the time, but this would be one of
the most important scientific voyages in history.
Observations Aboard the Beagle
BTW: The HMS Beagle is a ship! (In case you didn't catch that!)
Darwin filled his notebooks with observations about the
characteristics and habitats of the different species he
saw. Darwin wanted to explain the biological diversity he
observed in a scientific way. He looked for larger patterns
into which his observations might fit.
As he traveled, Darwin noticed three distinctive patterns of
biological diversity: (1) Species vary globally, (2) species
vary locally, and (3) species vary over time.
Charles Darwin & Species
Charles Darwin observed many different species
while on his trip. Scientifically, a species is defined
as reproductively distinct groups of organisms that
can be classified based on morphological,
behavioral, and molecular structures.
Do I have to know the definition of a species?
YES!
B5.2a Describe species as reproductively distinct groups of
organisms that can be classified based on morphological,
behavioral, and molecular structures.
Species Vary Globally
Darwin noticed that different, yet ecologically similar, animal species inhabited
separated, but ecologically similar, habitats around the globe.
IN OTHER WORDS: He found similar species in similar habitats around the
world, but they all had adaptations specific to their environment.
For example, Darwin found flightless, ground-dwelling birds called rheas living
in the grasslands of South America. Rheas look and act a lot like ostriches. Yet
rheas live only in South America, and ostriches live only in Africa. When
Darwin visited Australia’s grasslands, he found another large flightless bird, the
emu.
Darwin also noticed that rabbits and other species living in European
grasslands were missing from the grasslands of South America and Australia.
Australia’s grasslands were home to kangaroos and other animals that were
found nowhere else.
What did these patterns of geographic distribution mean?
Species Vary Over Time
Darwin also collected fossils, which are the
preserved remains or traces of ancient
organisms.
Darwin noticed that some fossils of extinct
animals were similar to living species.
One set of fossils unearthed by Darwin
belonged to the long-extinct glyptodont, a
giant armored animal similar to the armadillo.
Darwin wondered if the armadillo might be
related to the ancient glyptodont.
Why had glyptodonts disappeared? And why
did they resemble armadillos?
Darwin put it all together
On the voyage home, Darwin thought about the patterns he’d seen.
Darwin sent plant and animal specimens to experts for identification.
The Galápagos mockingbirds turned out to belong to three separate
species found nowhere else.
The little brown birds were actually all species of finches, also found
nowhere else, though they resembled a South American finch
species.
The same was true of Galápagos tortoises, marine iguanas, and
many plants that Darwin had collected on the islands.
Darwin put it all together
Darwin began to wonder whether different Galápagos species
might have evolved from South American ancestors.
He spent years actively researching and filling notebooks with ideas
about species and evolution.
The evidence suggested that species are not fixed and that they
could change by some natural process.
How do we classify living things?
Standard B2.4A
Explain that living things can be classified based on
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Structural (bones),
Embryology (embryo during development), &
Molecular (DNA sequence) evidence.
Homologous Structures
Homologous bones, as shown by color-coding,
support the differently-shaped front limbs of
modern vertebrates.
Homologous Structures
These limbs evolved, with modifications, from the front limbs
of a common ancestor whose bones resembled those of an
ancient fish.
Similarities and differences among homologous structures
help determine how recently species shared a common
ancestor.
For example, the front limbs of reptiles and birds are more
similar to each other than either is to the front limb of an
amphibian or mammal. This similarity—among many
others—indicates that the common ancestor of reptiles and
birds lived more recently than the common ancestor of
reptiles, birds, and mammals.
Embryology
Researchers noticed a long time ago that
the early developmental stages of many
animals with backbones (called
vertebrates) look very similar. Recent
observations make clear that the same
groups of embryonic cells develop in the
same order and in similar patterns to
produce many homologous tissues and
organs in vertebrates.
Similar patterns of embryological
development provide further evidence that
organisms have descended from a
common ancestor. Evolutionary theory
offers the most logical explanation for
these similarities in patterns of
development.
Life’s Common Genetic Code
All living cells use information coded in DNA and RNA to carry information
from one generation to the next and to direct protein synthesis. This genetic
code is nearly identical in almost all organisms, including bacteria, yeasts,
plants, fungi, and animals.
This compares a small portion of the DNA for the same gene in three
animals—a mouse, a whale, and a chicken. This similarity in genetic code is
powerful evidence that all organisms evolved from common ancestors.
Genes as Derived Characters
In general, the more derived genetic characters two
species share, the more recently they shared a common
ancestor and the more closely they are related in
evolutionary terms.
All organisms carry genetic information in their DNA
passed on from earlier generations.
A wide range of organisms share a number of genes
and show important homologies that can be used to
determine evolutionary relationships.
More about DNA & Evolution
All DNA (base sequences) in living things is very similar.
Remembering back a few units, WHAT DOES DNA
CODE FOR? Proteins
Proteins are a chain of amino acids that has been folded
and shaped a certain way. Each protein has a specific
function. Some make our bodies look the way they do,
some allow substances to pass in and out of our cells,
and some help chemical reactions in our bodies take
place. Basically, PROTEINS DO IT ALL!
More about DNA & Evolution
If DNA codes for Proteins, and the DNA of living
things is basically the same, that means all living
things mostly have the same proteins.
Therefore, the more similar the DNA and Protein
sequences, the more closely two organisms are
related.
Do you get it? Let's check!
Describe the following standards IN YOUR OWN WORDS
using complete sentences:
B5.2a Describe species as reproductively distinct groups of
organisms that can be classified based on morphological,
behavioral, and molecular structures.
B2.4A Explain that living things can be classified based on
structural, embryological, and molecular (relatedness of DNA
sequence) evidence.
B5.2b Explain that the degree of kinship between
organisms or species can be estimated from similarity of their
DNA and protein sequences.
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B5.1f Explain, using examples, how the fossil
record, comparative anatomy, and other
evidence supports the theory of evolution.
B2.4d Analyze the relationships among
organisms based on their shared physical,
biochemical, genetic, and cellular
characteristics and functional processes.
B5.1c Summarize the relationships
between present-day organisms and those
that inhabited the Earth in the past (e.g.,
use fossil record, embryonic stages,
homologous structures, chemical basis).
The Age of Earth and Fossils
How do fossils help to document the descent of
modern species from ancient ancestors?
Many recently discovered fossils form series that
trace the evolution of modern species from extinct
ancestors.
The Age of Earth
Evolution takes a long time. If life has evolved, then
Earth must be very old.
In Darwin's lifetime, scientists argued that Earth was
indeed very old, but technology in their day couldn’t
determine just how old.
Geologists now use radioactivity to establish the age of
certain rocks and fossils. Radioactive dating indicates
that Earth is about 4.5 billion years old—plenty of time
for evolution by natural selection to take place.
Click here for an explanation.
Recent Fossil Finds
Darwin’s study of fossils had convinced him and other
scientists that life evolved, but paleontologists in 1859
hadn’t found enough fossils of intermediate forms of life
to document the evolution of modern species from their
ancestors.
Since Darwin, paleontologists have discovered
hundreds of fossils that document intermediate stages
in the evolution of many different groups of modern
species.
Recent Fossil Finds
One recently discovered fossil series documents the
evolution of whales from ancient land mammals. The
exceptions to the reconstructions are the modern
Mysticete and Odontocete.
Recent Fossil Finds
The limb structure of
Ambulocetus (“walking
whale”) suggests that
these animals could both
swim in shallow water
and walk on land.
Recent Fossil Finds
The hind limbs of
Rodhocetus were short
and probably not able to
bear much weight.
Paleontologists think
that these animals spent
most of their time in the
water.
Recent Fossil Finds
Basilosarus had a
streamlined body and
reduced hind limbs.
These skeletal features
suggest that Basilosarus
spent its entire life
swimming in the ocean.
Recent Fossil Finds
Modern whales retain
reduced pelvic bones and,
in some cases, upper and
lower limb bones. However,
these structures no longer
play a role in locomotion.
Recent Fossil Finds
Other recent fossil finds connect the dots
between dinosaurs and birds, and between fish
and four-legged land animals.
All historical records are incomplete, and the
history of life is no exception. The evidence we
do have, however, tells an unmistakable story of
evolutionary change.
Comparing Anatomy and
Embryology
What do homologous structures and similarities in
embryonic development suggest about the process
of evolutionary change?
Evolutionary theory explains the existence of
homologous structures adapted to different
purposes as the result of descent with modification
from a common ancestor.
Comparing Anatomy and
Embryology
By Darwin’s time, scientists had noted that all
vertebrate limbs had the same basic bone
structure. For example, the front limbs of
amphibians, reptiles, birds, and mammals contain
the same basic bones.
Evolutionary Classification
What is the goal of evolutionary classification?
The goal of phylogenetic systematics, or
evolutionary classification, is to group species into
larger categories that reflect lines of evolutionary
descent, rather than overall similarities and
differences.
Clades
A clade is a group of species that includes a
single common ancestor and all descendants of
that ancestor—living and extinct.
A clade must must include all species that are
descended from a common ancestor, and cannot
include any species that are not descended from
that common ancestor.
Tracking lineage Using
Cladograms
Each node represents the last point at which the new
lineages shared a common ancestor. The bottom, or
“root,” of the tree represents the common ancestor
shared by all organisms on the cladogram.
Tracking lineage
A cladogram’s branching patterns indicate degrees of
relatedness among organisms.
Because lineages 3 and 4 share a common ancestor
more recently with each other than they do with lineage 2,
you know that lineages 3 and 4 are more closely related
to each other than they are with lineage 2.
Tracking lineage
Likewise, lineages 2, 3, and 4 are more closely
related, in terms on ancestry, with each other
than any of them is to lineage 1.
Tracking lineage
This cladogram represents current hypotheses about
evolutionary relationships among vertebrates.
Note that in terms of ancestry, amphibians are more
closely related to mammals than they are to rayfinned fish!
Reading Cladograms
This cladogram shows a simplified phylogeny of
the cat family.
Reading Cladograms
The lowest node represents the last common
ancestor of all four-limbed animals—members of
the clade Tetrapoda.
Reading Cladograms
The forks show the order in which various groups
branched off over the course of evolution.
Reading Cladograms
The trait of four limbs appeared before the trait of
hair in the history of the cat’s lineage.
IN YOUR NOTES:
Using the cladogram below, describe how closely the
following groups are related to MAMMALS using
complete sentences: Sharks, Snakes, and Crocodiles
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B5.3e Explain how changes at the gene level
are the foundation for changes in populations
and eventually the formation of a new species.
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B5.2c Trace the relationship between
environmental changes and changes in the
gene pool, such as genetic drift and isolation
of subpopulations.
Lesson Overview
Genes and Variation
Evolution & Genes
Darwin developed his theory of evolution
without knowing how heritable traits passed
from one generation to the next or where
heritable variation came from.
Lesson Overview
Genes and Variation
Genetics Joins Evolutionary Theory
How is evolution defined in genetic terms?
In genetic terms, evolution is any change in the relative
frequency of alleles in the gene pool of a population over time.
Researchers discovered that heritable traits are controlled by
genes. Changes in genes and chromosomes generate variation.
For example, all of these children received their genes from the
same parents, but they all look different.
Lesson Overview
Genes and Variation
Genotype and Phenotype in Evolution
QUICK REVIEW
An organism’s genotype is the particular combination of alleles
it carries. Such as AA or Aa.
An individual’s genotype, together with environmental
conditions, produces its phenotype.
Phenotype includes all physical, physiological, and behavioral
characteristics of an organism. Such as wide spaced eyes.
Lesson Overview
Genes and Variation
Genotype and Phenotype in Evolution
Natural selection (The process by which organisms with
variations most suited to their local environment survive and
leave more offspring) acts directly on phenotype, not
genotype.
Remember, phenotype is controlled by genes and by
environmental conditions.
Some individuals have phenotypes that are better suited to
their environment than others. These individuals produce
more offspring and pass on more copies of their genes to the
next generation.
Lesson Overview
Genes and Variation
Populations and Gene Pools
A population is a group of individuals of the same species that
mate and produce offspring.
A gene pool consists of all the genes, including all the different
alleles for each gene that are present in a population.
Researchers study gene pools by examining the relative
frequency of an allele. The relative frequency of an allele is the
number of times a particular allele occurs in a gene pool,
compared with the number of times other alleles for the same
gene occur.
Lesson Overview
Genes and Variation
For example, this diagram shows the gene pool for fur color in
a population of mice.
Lesson Overview
Genes and Variation
Populations and Gene Pools
Evolution is any change in the relative frequency of
alleles in the gene pool of a population over time.
Natural selection operates on individuals, but
resulting changes in allele frequencies show up in
populations. Populations, rather than individuals,
evolve.
B5.3e Explain how changes at the gene level are the foundation for changes in
populations and eventually the formation of a new species.
Lesson Overview
Genes and Variation
Describe the following standard IN YOUR
OWN WORDS using complete
sentences:
B5.3e Explain how changes at the gene
level are the foundation for changes in
populations and eventually the formation
of a new species.
Genes and Variation
Lesson Overview
Genetic Drift
What is genetic drift?
In small populations, individuals that carry a particular allele
may leave more descendants than other individuals, just by
chance. Over time, a series of chance occurrences can cause an
allele to become more or less common in a population.
B5.2c Trace the relationship between environmental
changes and changes in the gene pool, such as
genetic drift and isolation of subpopulations.
Lesson Overview
Genes and Variation
Genetic Drift
Genetic drift occurs in small populations
when an allele becomes more or less
common simply by chance. Genetic drift is a
random change in allele frequency.
Lesson Overview
Genes and Variation
An example of Genetic Drift
The founder effect occurs when allele frequencies change as a result of the
migration of a small subgroup of a population.
Two groups from a large, diverse population could produce new populations
that differ from the original group.
Lesson Overview
Genes and Variation
Factors such as natural selection and genetic drift can change the relative
frequencies of alleles in a population, but this alone does not lead to development
of a new species.
How does one species become two?
Lesson Overview
Genes and Variation
Isolating Mechanisms
Factors such as natural selection and genetic drift can change
the relative frequencies of alleles in a population, but this alone
does not lead to development of a new species.
How does one species become two? What types of isolation
lead to the formation of new species?
When populations become reproductively isolated, they can
evolve into two separate species. Reproductive isolation can
develop in a variety of ways, including behavioral isolation,
geographic isolation, and temporal isolation.
Lesson Overview
Genes and Variation
Making two species from one
Reproductive isolation occurs when a population splits into
two groups and the two populations no longer interbreed. When
populations become reproductively isolated, they can evolve
into two separate species. Speciation is the formation of a new
species. A species is a population whose members can
interbreed and produce fertile offspring.
Lesson Overview
Genes and Variation
Making two species from one
Behavioral isolation occurs when two populations that are capable
of interbreeding develop differences in courtship rituals or other
behaviors.
Geographic isolation occurs when two populations are separated
by geographic barriers such as rivers, mountains, or bodies of water.
For example, the Kaibab squirrel is a subspecies of the Abert’s
squirrel that formed when a small population became isolated on
the north rim of the Grand Canyon. Separate gene pools formed,
and genetic changes in one group were not passed on to the other.
Lesson Overview
Genes and Variation
Making two species from one
Temporal isolation happens when two or more species reproduce
at different times.
For example, three species of orchid live in the same rain forest.
Each species has flowers that last only one day and must be
pollinated on that day to produce seeds. Because the species bloom
on different days, they cannot pollinate each other.
Lesson Overview
Genes and Variation
Galapagos Finches & Geographic Isolation
Darwin hypothesized that the Galápagos finches had descended from a
common ancestor.
He proposed that natural selection shaped the beaks of different bird
populations as they became adapted to eat different foods.
Lesson Overview
Genes and Variation
Speciation in Darwin’s Finches
What is a current hypothesis about Galápagos finch
speciation?
In this hypothesis, speciation in Galápagos finches occurred by
founding of a new population, geographic isolation, changes in
the new population’s gene pool, behavioral isolation, and
ecological competition.
Lesson Overview
Genes and Variation
IN YOUR NOTES:
Answer the following IN YOUR OWN WORDS using complete
sentences (Use the following slides):
Explain how the species in the picture could have evolved from just
one species. Begin with the Founder effect & Geographic Isolation.
Lesson Overview
Genes and Variation
Founders Arrive
Many years ago, a few finches from
South America—species M—arrived
on one of the Galápagos islands, as
shown in the figure.
Because of the founder effect, the
allele frequencies of this founding
finch population could have differed
from those in the South American
population.
Lesson Overview
Genes and Variation
Changes in Gene Pools
Over time, populations on each
island adapted to local
environments.
Natural selection could have
caused two distinct populations to
evolve (A and B), each
characterized by a new
phenotype.
Lesson Overview
Genes and Variation
Competition and Continued Evolution
Birds that are most different from
each other have the highest
fitness. More specialized birds
have less competition for food.
Over time, species evolve in a way
that increases the differences
between them, and new species
may evolve (C, D, and E).
Click here:
http://science.discovery.com/videos/100-greatestdiscoveries-shorts-natural-selection.html
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B5.3C Give examples of ways in which genetic
variation and environmental factors are causes
of evolution and the diversity of organisms.
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B5.3B Describe the role of geographic
isolation in speciation.
Just a reminder...
Geographic isolation occurs when two
populations are separated by geographic
barriers such as rivers, mountains, or bodies of
water.
Click here for an animated tutorial about
geographic isolation: http://life9e.sinauer.com/life9e/pages/23/232001.html
The Kaibab
squirrel (Sciurus
aberti
kaibabensis )
(left) is only
found on the
Kaibab Plateau
north of the
Grand Canyon,
while the related
Abert’s squirrel
(Sciurus aberti
aberti ) (right) is
found on the
south rim of the
Grand Canyon.
Kaibab squirrel (left) and Abert’s squirrel (right).
Kaibab & Abert's Squirrels –
Geographic Isolation
When two populations are separated by geographic barriers
such as rivers, mountains, or bodies of water, geographic
isolation occurs. The Abert's squirrel in the previous slide , for
example, lives in the Southwest. About 10,000 years ago, a
small population of Abert's squirrels became isolated on the
north rim of the Grand Canyon. Separate gene pools formed.
Genetic changes that appeared in one group were not
passed to the other. Natural selection and genetic drift
worked separately on each group and led to the formation of
a distinct subspecies, the Kaibab squirrel. The Abert's and
Kaibab squirrels are very similar, indicating that they are
closely related. However the Kaibab squirrel differs from the
Abert's squirrel in significant ways, such as fur coloring.
The populations of Tamarin monkeys are separated on the sides of
the Amazon River. Where the river tributary is wide and individuals
on opposite banks do not interbreed, the populations are diverging
toward separate species. Where the river tributary is narrow, the
individuals still interbreed.
B5.3B Describe the role of geographic isolation in speciation.
So can you....
...describe the role of geographic isolation in
speciation?
Geographic isolation is when a part of a
population becomes isolated (cut off) due to a
geographic barrier (rivers, mountains, bodies of
water). The isolated organisms develop a
separate gene pool as they adapt to their local
environment over time. As a result of the
geographic isolation, the isolated organisms
evolve separately from the original population and
a new species is formed (speciation).
B5.3C Give examples of ways in which genetic variation and environmental
factors are causes of evolution and the diversity of organisms.
There are three primary sources of genetic variation, all of
which can cause evolution to occur.
Mutations are changes in the DNA. A single mutation can
have a large effect, but in many cases, evolutionary change is
based on the accumulation of many mutations.
Gene flow is any movement of genes from one population to
another and is an important source of genetic variation.
Sex can introduce new gene combinations into a population.
This genetic shuffling is another important source of genetic
variation.
Quick refresher on Mutations
What is a Mutation?
Mutation is a change in DNA, the hereditary material of life. An organism’s
DNA affects how it looks, how it behaves, and its physiology—all aspects of
its life. So a change in an organism’s DNA can cause changes in all
aspects of its life.
Mutations are random.
Mutations can be beneficial, neutral, or harmful for the organism, but
mutations do not “try” to supply what the organism “needs.” In this respect,
mutations are random—whether a particular mutation happens or not is
unrelated to how useful that mutation would be.
Not all mutations matter to evolution.
Since all cells in our body contain DNA, there are lots of places for
mutations to occur; however, not all mutations matter for evolution. Some
mutations occur in non-reproductive cells and won’t be passed onto
offspring.
Click here: http://dsc.discovery.com/videos/assignment-discovery-shorts-darwinmutation.html
Adapt (Mutate) or Die!
Environmental change and isolation of groups of organisms play
an important role in evolution.
Environmental change is any change in an environment to which
an organism must adapt or die.
Change can be gradual, such as when mountains or deserts
form, other species die out, or new species evolve. These things
can take millions of years. Change to an environment can also be
quick, such as floods, volcanoes, or earthquakes. It can also be
caused not by change to the environment itself, but by the
organism's movement to a different environment.
Adapt (Mutate) or Die!
Erupting volcanoes cause sudden, drastic change in an area,
forcing organisms to evolve rapidly to adapt to the new
environment.
This penguin's ancestors looked much like other birds. As
their environment became colder and wetter (possibly
because of their migration), the birds evolved many traits to
help them survive in the changed environment. These traits
are called adaptations.
Adapt (Mutate) or Die!
Change in an organism's environment forces the organism to
adapt to fit the new environment, eventually causing it to evolve
into a new species. For example, if a species of animal is
mostly limited to eating one kind of leaf, and a change occurs: a
fungus attacks and kills most of that kind of plant, the animal
has to evolve either to fight the fungus or to eat something else.
Isolation means that organisms of the same species are
separated, and happens when there is something between the
organisms that they can't cross. Organisms become isolated as
a result of environmental change. The cause of isolation can be
gradual, like when mountains or deserts form, or continents
split apart. It can also be quick, such as organisms being blown
to different places by a storm or tsunami (tidal waves).
When organisms become isolated the two
groups are also not able to reproduce together,
so variations and mutations that occur in one
group are not necessarily found in the other
group. The longer the groups are isolated, the
more different they are. They eventually
become different species. Moreover, if there is
a change in the environment of one group it
does not necessarily occur in the environment
of the other. So they will evolve and adapt
differently.
The finches and other organisms that Darwin
found on the Galapagos Islands are examples
that demonstrate the effect that environmental
change and isolation can have on a species.
B5.3C Give examples of ways in which genetic variation and environmental
factors are causes of evolution and the diversity of organisms.
Rivers change course, mountains rise, continents
drift, organisms migrate, and what was once a
continuous population is divided into two or more
smaller populations in a process called
geographic isolation.

B5.1A Summarize the major concepts of
natural selection (differential survival and
reproduction of chance inherited variants,
depending on environmental conditions).

B5.1B Describe how natural selection
provides a mechanism for evolution.

B5.1d Explain how a new species or
variety originates through the evolutionary
process of natural selection
What is Natural Selection?
Click here: http://dsc.discovery.com/videos/assignment-discovery-shorts-naturalselection.html
Natural selection is one of the basic mechanisms of
evolution, along with mutation, migration, and genetic
drift. Darwin's grand idea of evolution by natural selection
is relatively simple but often misunderstood. To find out
how it works, imagine a population of beetles:
There is variation in traits.
For example, some beetles
are green and some are brown.
What is Natural Selection?
There is differential reproduction.
Since the environment can't support unlimited population
growth, not all individuals get to reproduce to their full
potential. In this example, green beetles tend to get
eaten by birds and survive to reproduce less often than
brown beetles do.
What is Natural Selection?
There is heredity.
The surviving brown beetles have brown baby beetles
because this trait has a genetic basis.
What is Natural Selection?
End result:
The more advantageous trait, brown coloration, which
allows the beetle to have more offspring, becomes more
common in the population. If this process continues,
eventually, all individuals in the population will be brown.
B5.1B Describe how natural selection provides a mechanism for evolution.
B5.1d Explain how a new species or variety originates through the evolutionary
process of natural selection.
What about fitness?
Biologists use the word fitness to describe how good a particular
genotype is at leaving offspring in the next generation relative to how
good other genotypes are at it. So if brown beetles consistently leave
more offspring than green beetles because of their color, you'd say
that the brown beetles had a higher fitness.
The brown beetles have a greater fitness relative to the green beetles.
Of course, fitness is a relative thing. A genotype's fitness depends on
the environment in which the organism lives. The fittest genotype
during an ice age, for example, is probably not the fittest genotype
once the ice age is over.
How does Evolution Really Work?
Take about 7 minutes to watch the PBS video,
“How does evolution really work?”
Downloaded on your computer
Misconceptions about Natural Selection
Because natural selection can produce amazing adaptations, it's tempting to
think of it as an all-powerful force, urging organisms on, constantly pushing
them in the direction of progress — but this is not what natural selection is
like at all.
First, natural selection is not all-powerful; it does not produce perfection. If
your genes are "good enough," you'll get some offspring into the next
generation — you don't have to be perfect. This should be pretty clear just by
looking at the populations around us: people may have genes for genetic
diseases, plants may not have the genes to survive a drought, a predator
may not be quite fast enough to catch her prey every time she is hungry. No
population or organism is perfectly adapted.
Second, it's more accurate to think of natural selection as a process rather
than as a guiding hand. Natural selection is the simple result of variation,
differential reproduction, and heredity — it is mindless and mechanistic. It has
no goals; it's not striving to produce "progress" or a balanced ecosystem.
Misconceptions about Natural Selection
Evolution does not work this
way! This is why "need," "try,"
and "want" are not very
accurate words when it comes
to explaining evolution. The
population or individual does
not "want" or "try" to evolve,
and natural selection cannot
try to supply what an organism
"needs." Natural selection just
selects among whatever
variations exist in the
population. The result is
evolution.
The Overall Mechanism
of Natural Selection
The individuals with the more advantageous traits
(the better phenotype) survive better and
therefore are able to reproduce more, increasing
the frequency of individuals with the
advantageous traits in the next generation.
Watch the video “Evolution Library: Tale of the
Peacock” to gain a quick reminder of how traits
are passed on.
Natural Selection & Mimicry
First, watch the video “Evolution Library: The
Evolution of Camouflage” saved on your
computer.
Now, we will complete an activity about Natural
Selection using M&Ms. But first, watch the
following narrated animation:
http://bcs.whfreeman.com/thelifewire/content/chp2
3/2302001.html
•
B5.1e Explain how natural selection leads to
organisms that are well-suited for the environment
(differential survival and reproduction of chance
inherited variants, depending upon environmental
conditions).
•
B2.4B Describe how various organisms have
developed different specializations to accomplish a
particular function and yet the end result is the same
(e.g., excreting nitrogenous wastes in animals,
obtaining oxygen for respiration).
•
B2.4C Explain how different organisms
accomplish the same result using different
structural specializations (gills vs. lungs vs.
membranes).
Homologies – new & review
Go to the following webpage, read the
information, and follow the instructions. There are
several questions in your notesheet that
correspond to the webpage.
http://evolution.berkeley.edu/evolibrary/article/0_0_0/similarity_hs_01
Stop the activity after it asks you about dolphins
and sharks (quiz question).
Then, watch this tetrapod video (4 min):
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_03.html
•
B5.3A Explain how natural selection acts on individuals, but it is
populations that evolve. Relate genetic mutations and genetic variety
produced by sexual reproduction to diversity within a given population.
•
B5.3d Explain how evolution through natural selection can result in changes in
biodiversity.
•
B5.1g Illustrate how genetic variation is preserved or eliminated from a
population through natural selection (evolution) resulting in biodiversity.
•
B3.4B Recognize and describe that a great diversity of species increases the
chance that at least some living organisms will survive in the face of
cataclysmic changes in the environment.
REPEAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! In case you haven't noticed,
the standards repeat themselves! Watch this 10 minute video
lecture to refresh your memory:
http://www.neok12.com/php/watch.php?v=zX600e7a54016d537f470e55&t=NaturalSelection
In your notes: answer the following by watching the
video lecture, using your notes, or looking in the
book:
•
•
•
•
•
•
What is NATURAL SELECTION?
Explain how Natural Selection can help cause the
evolution of a species.
How do genetic mutations and sexual
reproduction help cause the evolution of a
species?
What is biodiversity?
Does biodiversity increase or decrease because
of natural selection? Explain.
Why is a great diversity of species (caused by
sexual reproduction) beneficial?

B5.3f Demonstrate and explain how biotechnology can
improve a population and species.
Watch the following videos. In your notesheet, write HOW the
bioengineering (genetic engineering) can affect biodiversity.
Use complete sentences (2 per video).
http://www.teachersdomain.org/resource/tdc02.sci.life.gen.btc
orn/
http://www.teachersdomain.org/resource/tdc02.sci.life.gen.bre
eding/
http://www.pbs.org/wgbh/harvest/etc/video.html
The Last Standard!!!!