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Changes Over Time
Table of Contents
Darwin’s Theory
Evidence of Evolution
The Fossil Record
Changes Over Time
What is Evolution?
-Evolution is the change in the hereditary features
of a species over time.
*A species is a group of similar organisms that
can mate with each other and produce fertile
offspring. Today, we have identified more than
1.7 million species.
*How do species change over time?
Changes Over Time
Lamarck’s Theory
-Jean Baptiste de Lamarck (1809):
*Proposed the “Theory of
Acquired Characteristics”
which states that species
change over time by keeping
traits that their parents
developed during their lifetime.
*This theory was rejected once
we understood genetics.
Changes Over Time
Darwin’s Theory
-Charles Darwin (1859):
*Proposed the “Theory of
Natural Selection”.
*This theory states that
organisms with traits best
suited to their environment
are more likely to survive
and therefore pass on
these favorable traits.
Changes Over Time - Darwin’s Theory
*Darwin was a naturalist on the
HMS Beagle.
*In Dec. 1831, he began a 5 year
voyage to collect and study plants
and animals from all over the world.
Changes Over Time
*One stop on the
voyage was The
Galapagos Islands
(a group of 19 small
islands off the coast
of Ecuador).
Changes Over Time
*Much of Darwin’s Theories were
developed after studying the
unique plants and animals of
the Galapagos Islands.
Changes Over Time
*Darwin spent over 20 years collecting
his thoughts and writing a book.
*He presented his book, “On the Origin
of Species by Means of Natural
Selection”, in 1859.
Changes Over Time - Darwin’s Theory
Four Basic Points of Natural Selection
-Overproduction—organisms produce more offspring than
can possibly survive.
-Variation—many differences are found among individuals
of a species due to meiosis and genetic inheritance.
Changes Over Time - Darwin’s Theory
-Competition—some variations allow members of a
population to survive and reproduce better than others.
-Selection—over time, offspring of individuals with helpful
variations make up more and more of a population.
Changes Over Time
Variations and Adaptations
-A variation is any difference
between individuals of the
same species.
-An adaptation is any trait
that helps an organism
survive and reproduce.
*Examples: webbed feet on
a duck: gills on a fish
Changes Over Time
-If enough variations occur in a
population over time, a new species
could result.
-The movement of individuals into or out
of a population helps to bring about
more variations.
Changes Over Time
What Brings About Change?
A sudden change in the
climate or environment can
bring about evolutionary
change by suddenly
favoring one variation over
Example: Peppered moths
of England. Eventually, a
new species could form if the
environmental change is
drastic enough.
Changes Over Time - Evidence of Evolution
Geographic isolation can
also bring about
evolutionary change.
Example: Kaibab and
Abert’s Squirrels.
These two kinds of
squirrels have been
isolated from one another
for a long time. Eventually
this isolation may result in
two different species.
Changes Over Time
Evidence for Evolution
-Similarities in Early
*All vertebrate embryos
resemble each other early
in development.
These similarities show an
evolutionary relationship
among all vertebrates.
Changes Over Time - Evidence of Evolution
-Homologous Structures—similar structures that
related species have inherited from a common
ancestor. Example: the bones in a dolphin’s
flipper, a bird’s wing, and a dog’s leg
Changes Over Time
-Vestigial structures—body parts that are
reduced in size and do not appear to have a
Examples: human appendix, hip bones in
whales and snakes.
Scientists believe these once functioned in
an ancestor.
Changes Over Time
-DNA and Protein
organisms that are close
relatives have similar
Example: The DNA of
humans and chimps differs
by less than 1%.
This supports the idea that
primates all evolved from a
common ancestor.
Changes Over Time
-Development of chemical resistance—
organisms that have genes that make
them resistant to a particular chemical will
be the only ones to survive in the
presence of that chemical to pass on their
traits. Examples:
*Antibiotic resistant bacteria
*Pesticide resistant insects
Changes Over Time
-Fossil Evidence
*A fossil is the preserved remains of an
organism that lived in the past.
*Fossils show that many organisms from
the past are very different than
organisms alive today.
*Types of fossils:
Changes Over Time - The Fossil Record
Click the Video button to watch a movie about fossils.
Changes Over Time
Petrified Fossils
Rock imprints or molds
Stone Casts
Preserved remains in amber or ice
Changes Over Time - The Fossil Record
How Do Fossils Form?
Most fossils form when organisms that die
become buried in sediments.
Changes Over Time - The Fossil Record
Fossil Formation Activity
Click the Active Art button to open a browser window and
access Active Art about fossil formation.
Changes Over Time
Dating Fossils
Two methods for dating fossils:
Relative dating —fossils are dated
according to the layer of rock in which they
are found. This is just an estimate.
Radioactive dating —fossils are dated by
measuring the amount of radioactive
material present. This is more accurate.
Changes Over Time - The Fossil Record
Radioactive Decay
The half life of potassium-40, a
radioactive element, is 1.3 billion
years. This means that half of
the potassium-40 in a sample
will break down into argon-40
every 1.3 billion years. The
graph shows the breakdown of a
1-gram sample of potassium-40
into argon-40 over billions of
Changes Over Time - The Fossil Record
Radioactive Decay
Reading Graphs:
What does the red line
represent? What does the
blue line represent?
The red line represents the
amount of potassium-40. The
blue line represents the
amount of argon-40.
Changes Over Time - The Fossil Record
Radioactive Decay
Reading Graphs:
At 2.6 billion years ago, how
much of the sample consisted
of potassium-40? How much
of the sample consisted of
Potassium-40–100%; argon40–0%
Changes Over Time - The Fossil Record
Radioactive Decay
Reading Graphs:
At what point in time do the
two graph lines cross?
About 1.3 billion years
Changes Over Time - The Fossil Record
Radioactive Decay
Interpreting Data:
At the point where the graph
lines cross, how much of the
sample consisted of
potassium-40? How much
consisted of argon-40?
Explain why this is the case.
50% of each; the half-life of
potassium-40 is 1.3 billion
years, which means that half
will break down into argon-40
every 1.3 billion years.
Changes Over Time
Fossil Record and Geologic Time Scale
Geologic Time Scale —a calendar of Earth’s
Using the fossil record (all the fossils
scientists have collected) and fossil
dating techniques, scientists have
developed the Geologic Time Scale.
Changes Over Time - The Fossil Record
Earth’s History as a Clock
Fossils found in rock layers tell the history of life on Earth.
The history of life can be compared to 12 hours on a clock.
Changes Over Time - The Fossil Record
Precambrian Time and the Paleozoic Era
Changes Over Time - The Fossil Record
Mesozoic and Cenozoic Eras
Changes Over Time
Combining Evidence
-DNA evidence is a newer source of evidence.
-In most cases, evidence from DNA and protein
structure has confirmed conclusions based on
fossils, embryos, and body structure.
-In some cases, scientists have had to change
their hypothesis.
-Scientists can use the combined evidence of
species relationships to draw
branching trees —diagrams that show how
different groups of organisms are related.
Changes Over Time - Evidence of Evolution
A Branching Tree
This branching tree shows how scientists now think that
raccoons, lesser pandas, giant pandas, and bears are
Changes Over Time
How Fast Does Evolution Occur? Two Theories
-Gradualism—very slow
change from one species
to another.
*Involves intermediate
*Supported by some
fossil records (like the
horse) but not all.
Changes Over Time
-Punctuated Equilibrium —more rapid
evolution of a species brought about by
the mutation of just a few genes.
*Supported by some fossil records and
bacteria experiments.
-Today, scientists think both probably
Changes Over Time
Extinction and Evolution
-Extinction is the dying out of a species.
*Occurs naturally because the
environment is always changing.
Through natural selection, species
which are unable to adapt to a
changing world are removed.
*Earth’s history shows at least 4 mass
extinctions followed by rapid explosion
of new species.
Changes Over Time
Human’s role in extinction of species
-Human overpopulation and human
activities are contributing to the rapid
extinction of thousands of species.
*This led to the passage of the
Endangered Species Act of 1973. As
a result, many captive breeding
programs were established. They are
expensive and for some species, they
may be too late.
Changes Over Time - Darwin’s Theory
Relating Cause and Effect
In a graphic organizer, identify factors that cause natural
Overproduction: More offspring are
produced than can survive.
Variations: Members of the same species
Competition: Offspring compete for
Selection: Some variations make
individuals better fit for survival.
Environmental Change: Changes can
affect an individual’s survival.
Genes: Genes that help determine survival
are passed from parent to offspring.
Natural Selection
Changes Over Time - Darwin’s Theory
Links on Charles Darwin
Click the SciLinks button for links on Charles Darwin.
Changes Over Time
End of Section:
Darwin’s Theory
Changes Over Time - Evidence of Evolution
Identifying Supporting Evidence
Evidence consists of facts that can be confirmed by testing or
observation. As you read, identify the evidence that supports
the theory of evolution. Write the evidence in a graphic
organizer like the one below.
Fossils show that organisms that
lived in the past were very different
from organisms alive today.
Patterns of early development
show that some different
organisms look similar during their
early stages.
Similar body
structures in different species
show that the organisms shared
a common ancestor.
Changes Over Time - Evidence of Evolution
Links on Evolution
Click the SciLinks button for links on evolution.
Changes Over Time
End of Section:
Evidence of
Changes Over Time - The Fossil Record
Building Vocabulary
After you read the section, write a definition of each Key
Term in your own words.
Key Terms:
petrified fossil
fossil record
relative dating
gradualism dating
by minerals
are found
near contain
the fossil
record.which are unstable elements
that decay, or break down, into different elements.
A hollow space in the sediment in the shape of an
of a of
is the
time it
or part
an organism
is called
a mold.
takes for half of the atoms in a sample to decay.
A cast is a copy of the shape of the organism that
a mold.of fossils that scientists have collected are
called the fossil record.
Scientists use relative dating to determine which of
older. if no members of that species are
still alive.
technique called
allowsslowly but
that evolution
steadily. to determine the actual age of fossils.
Changes Over Time
End of Section:
The Fossil
Changes Over Time
Graphic Organizer
Fossil Formation
An organism dies in water.
The organism is buried under sediment.
Over millions of years, the sediments harden and become rock, and the
hard parts of the organism are replaced by minerals.
The fossil becomes exposed on the surface of a rock.
Changes Over Time
End of Section:
Graphic Organizer