Download The Environment and Change Over Time

The Environment and Change
Over Time
Chapter 6
6-1
Fossil Evidence
of Evolution
The Fossil Record
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The fossil record is made up of all the fossils ever
discovered on Earth.
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The fossil record provides evidence that species
have changed over time.
● Based on fossil evidence,
scientists can recreate
the physical appearance
of species that are no
longer alive on Earth.
How do fossils form?
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Usually only the hard parts of an animal remain
such as bones, teeth or shells
In plants, leaves, stems, roots, or seeds can leave
behind fossils.
Fossils rarely occur, and most form when an
organism dies and becomes buried in sediment.
Fossil Formation cont’
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The impression (imprint)
of an organism found in a
rock is called a mold
when it hardens.
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A cast is a fossil copy of
an organism in a rock
Trace Fossils- the preserved
evidence of the activity of an
organism.
Determining a Fossils age
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Instead of dating fossils
directly, scientists date the
rocks the fossils are
embedded inside.
If the age of the igneous
layers is known, it
is possible to estimate the
age of the sedimentary
layers—and the fossils
they contain—between
them.
Deeper fossils look less
like present day organisms
Fossils Over Time
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The geologic time scale is a chart that
divides Earth’s history into different time
units.
Extinctions
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Extinctions occur when the last
individual organism of a species dies.
A mass extinction occurs when many
species become extinct within a few
million years or less.
Extinctions can occur when
environments change and organisms
can’t adapt quickly enough
Extinctions cont’
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The fossil record contains evidence that
five mass extinction events have
occurred during the Phanerozoic eon.
Extinctions cont’
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The fossil record contains evidence of
the appearance of many new species
over time.
Biological evolution is the change
over time in populations of related
organisms
Biological evolution
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The fossil record
shows evidence
that horses
descended from
organisms for
which only fossils
exist today.
6-2
Theory of Evolution by
Natural Selection
In December 1831, the British naval ship
HMS Beagle set sail from England for a 5
year long trip around the world.
Charles Darwin
•Charles Darwin, a British
Naturalist was on board.
•A naturalist is a person who
studies plants and animals by
observing them.
•His job was to learn as much
as he could about the living
things he saw on the voyage.
Darwin’s Observations
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During the voyage, he observed many plants
and animals that he had never seen before.
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He wondered why there were so different
than the plants and animals in England.
In 1835, the Beagle
reached the
Galapagos Islands
- a group of small
islands in the Pacific
Ocean off the west
coast of South
America
Were there differences
between the Islands?
●Darwin
studied many animals on the islands &
noticed differences & similarities between them
Giant Galapagos Tortoises
For example, the tortoises on one
island had dome shaped shells and
on another island had saddle-shaped
shells.
Why?
Darwin found that each island in the
Galápagos had a different environment, and
tortoises looked different depending on
which island environment they inhabited.
Blue-footed booby
Red-footed booby
Land and Marine Iguanas
The Iguanas
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The Iguanas on the Islands
had large claws and the
Iguanas on the mainland had
smaller claws.
Why?
Large claws allowed the
Iguanas to hold on to the
slippery rocks to feed on
seaweed.
Small claws allowed the
Iguanas to climb trees where
they ate leaves.
Cormorants (large sea birds) were able
to fly on the mainland but could not fly
on the Islands.
Flightless Cormorant
Mainland Cormorant
Similarities and Differences
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Darwin observed that many of the
species on the Galapagos Islands were
similar to those on the mainland.
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Why?
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Where did they come from?
How did they get there?
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Darwin inferred that some of the
animals from mainland Ecuador came
over to the Islands
They might have been blown out to sea
during a storm or drifted on a log
millions of years ago
Darwin’s Finches
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Finches on the Galapagos Islands
differed slightly from the finches in
Ecuador too
The finches on each of the Galapagos
Islands were also different from each
other
Mainly the shape of their beaks and the
food they ate were different depending
what was available on their island
The finches had to adapt to life on their
island or they would die
Darwin’s Finches of the Galapagos
Darwin’s Theory
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Darwin realized the Galapagos animals came
from common ancestors, but had changed over
time & now had slight differences or variations.
– A variation is a slight difference in an inherited trait
of individual members of a species.
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Variations arise naturally in populations,
occurring in offspring as a result of sexual
reproduction.
– The #1 source of variations are genetic mutations,
which are changes in a gene
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Peppered Moths
Before 1850, black
peppered moths were rare
and white were more
common.
Natural Selection in action
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Several species of birds
eat the peppered moths.
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White moths blended
into their surroundings
and black moths were
eaten more frequently.
After the 1850’s…
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Soot and smoke from industrial
areas blackened nearby trees
Black moths became less visible
and white moths stood out and
became easy prey
More black moths survived and
produced more black moth
offspring
Population changed from mostly
light-colored moths to mostly
dark-colored moths
Darwin’s Theory
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Darwin believed these variations occurred
through the process of Natural Selection
Natural Selection is the process by which
organisms with favorable traits that help
them survive in their environments live
longer, compete better, and reproduce more
than those that do not have the better trait.
Natural selection explains how populations
change as their environments change.
Natural Selection (4 steps)
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1859 Darwin wrote
– The Origin of the Species
– In it, he says that evolution occurs by natural
selection
– Individuals that are better adapted to their
environment are more likely to survive and
reproduce
– “survival of the fittest”
1. Reproduction
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Most species naturally produces more
offspring than will survive to maturity
Starvation, disease, predators affect the size
of their population
Limited number survive to reproduction age
Offspring of the strongest organisms inherit
traits that help them survive in their
environment
2. Genetic Variation
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Offspring have slightly different traits
from one another
Some traits increase the chances of
survival and reproduction, others
decrease the chances of survival
These variations are inherited
3. Competition
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Natural environments do not have
enough food, water, and other
resources
Offspring fight for food, water, and other
resources
Some become prey for predators
Only the fittest (strongest) survive to
adulthood
4. Selection
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Offspring that are better adapted to the
environment will be naturally “selected”
to survive & reproduce to keep the
species going
Natural Selection in 4 steps
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1. Reproduction
Species produces more offspring than will survive
2. Genetic Variation
Offspring have different traits
Some traits increase chances of survival
3. Competition
Offspring fight for food, water, and other resources
Some become prey
The fittest survive to adulthood
4. Selection
Offspring better adapted to environment are more
likely to reproduce
Adaptations
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Through natural selection, a helpful variation
in one individual can spread to all members
of a population.
An adaptation is an inherited trait that
increases an organism’s chance of surviving
and reproducing in its environment.
Adaptations can be structural or behavioral
– Example: structures and behaviors for finding
food, for protection, and for moving from place to
place
Adaptations to Habitat
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Arctic hare– white fur in winter
provides
camouflage from
predators
• (structural adaptation)
Adaptations to Habitat
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Monkey– Grasping tail acts as
an extra hand to aid
movement through
trees
• (structural adaptation)
Adaptations to Habitat
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Cactus
– Waxy skin reduces water
loss from evaporation
• (structural adaptation)
Adaptations to Habitat
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Black Bear
– Hibernates to adapt to
seasonal changes
• (behavioral adaptation)
Artificial Selection
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The breeding of organisms for desired
characteristics is called selective
breeding
Darwin realized that changes caused
by selective breeding were much like
changes caused by natural selection,
but done by humans.
Humans can choose to breed
individuals with desired traits
– Farmers can choose to breed only corn
with plump corn kernels
– Dog breeders choose which dogs to
breed by selecting traits
What is a Species?
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A species is a group of similar
organisms that can mate with each
other and produce fertile offspring.
Species evolve so they can survive in
their changing environment.
Not all members of a species are strong
enough to evolve and survive.
How do new species form?
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Isolation or complete separation occurs
Over time new traits are developed
Formation of a new species can happen
in 3 steps:
1. Separation
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A portion of a population
becomes isolated from the
rest of the population by:
– newly formed canyon,
mountain range, lake
2. Adaptation
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If the population is divided, the
environment may also change and so
may the population that lives there
The separated groups may adapt to
better fit their environments
3. Division
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2 groups may become so different that
they can no longer interbreed
They are no longer the same species
Darwin’s Finches may have
evolved this way:
1.
2.
3.
4.
5.
6.
Some finches left the mainland and reached one of
the islands (separation)
The finches reproduced and adapted to the
environment (adaptation)
Some finches flew to a second island (separation)
The finches reproduced and adapted to a different
environment (adaptation)
Some finches flew back to the first island but could
no longer interbreed with those finches (division)
This process may have occurred over and over
again as the finches flew to the other islands
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1.Separation
– Portion of a population becomes isolated from the rest of the
population by:
• Newly formed canyon
• Mountain range
• Lake
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2.Adaptation
– As environment changes, separated groups adapt to their
new environment
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3.Division
– Groups of a population become so different they can no
longer interbreed
• Different species form
6-3
Biological Evidence of
Evolution
Evidence for Evolution
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Evolution is the process by
which populations accumulate
inherited changes over time
– Because of evolution, scientists
think that all living things share a
common ancestor
Evidence for common ancestry
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Homologous structures
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Homologous
structures are
body parts of
organisms that
are similar in
structure and
position but
different in
function.
Suggests a
common ancestor
Evidence for common ancestry
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Body parts that
perform a similar
function but
differ
in structure are
analogous
structures
Evidence for common ancestry
Remnants of hind-limb
bones are embedded inside
the whale’s body
●“Leftovers”
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Vestigial Structures
are body parts that
have lost their original
function through
evolution.
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Examples:
– Human Tail Bone
– Appendix
– Tonsils
– Wisdom teeth
Comparing DNA
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Looking at similarities
in DNA
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Human and
chimpanzee DNA 99%
identical
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Suggests common
ancestor
How are these species alike?
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Turtle
Chicken
Rat
Early development
Turtle
Chicken
Rat
Early development
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All have a tail
All have gill slits
They share a common ancestor
Comparing
Embryos
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Similar appearance
early in embryonic
development
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The science of the
development of
embryos from
fertilization to birth is
called embryology
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Suggest common
ancestor