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The Environment and Change
Over Time
Chapter 6
Fossil Evidence
of Evolution
The Fossil Record
The fossil record is made up of all the fossils ever
discovered on Earth.
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?
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’
 The
impression of an
organism found in a rock
is called a mold
cast is a fossil copy of
an organism in a rock
Trace Fossils- the preserved
evidence of the activity of an
Evidence that life has changed over time
 Oldest fossils are very simple
Determining a Fossils age
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
 Deeper fossils look less
like present day organisms
Fossils Over Time
 The
geologic time scale is a chart that
divides Earth’s history into different time
 Extinction
occurs 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’
 The
fossil record contains evidence that
five mass extinction events have
occurred during the Phanerozoic eon.
Extinctions cont’
 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
Biological evolution
 The
fossil record
shows evidence
that horses
descended from
organisms for
which only fossils
exist today.
Theory of Evolution by
Natural Selection
In December 1831, the British naval ship
HMS Beagle set sail in 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
During the voyage, he observed many plants
and animals that he had never seen before
 He wondered why there were so different
than the plants and animals in England.
 What do you think?
 This led him to his theory of Evolution by
Natural Selection.
In 1835, the Beagle
reached the
Galapagos Islands
- a group of small
islands in the Pacific
Ocean off the west
coast of South
Were there differences
between the Islands?
Darwin studied many animals on the islands
& noticed differences & similarities between
 For example, the tortoises on one island had
dome shaped shells and on another island
had saddle-shaped shells.
 The finches on each island had different size
and shaped beaks.
 Why?
 They had to adapt to their environment.
Giant Galapagos Tortoises
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
The Iguanas on the Islands had large claws
and the Iguanas on the mainland had smaller
 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.
Land Iguanas
Marine Iguanas
Marine Iguana
Mainland Iguana
 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
 Darwin
observed that many of the
species on the Galapagos Islands were
similar to those on the mainland.
 Why?
 Where
did they come from?
How did they get there?
 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
 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
 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 perish
Darwin’s Finches of the Galapagos
Darwin’s Theory
 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.
 Variations
arise naturally in populations,
occurring in offspring as a result of sexual
– The #1 source of variations are genetic mutations,
which are changes in a gene
 Genetic
changes to phenotype can be passed
on to future generations.
Darwin’s Theory
 Darwin
believed these variations occurred
through the process of Natural Selection
 Natural Selection is the process by which
organisms with favorable variations that help
them survive in their environments live
longer, compete better, and reproduce more
than those that do not have the variations.
 Natural selection explains how populations
change as their environments change.
Natural Selection (4 steps)
1858 Alfred Russell Wallace proposed a
theory of evolution
 1859 Darwin wrote
– The Origin of the Species
– In it, he says that evolution occurs by natural
– Individuals that are better adapted to their
environment are more likely to survive and
– “survival of the fittest”
1. Reproduction
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
2. Genetic Variation
 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
 Natural
environments do not have
enough food, water, and other
 Offspring fight for food, water, and other
 Some become prey for predators
 Only the fittest (strongest) survive to
4. Selection
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
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
Natural Selection in action
 Peppered
 Before 1850, dark
peppered moths were rare
and pale were more
 After 1850’s, dark
peppered moths became
more abundant in heavily
industrialized areas.
What caused the change?
Several species of birds
eat the peppered moths.
Pale moths blended into
their surroundings and
dark moths were eaten
more frequently.
After the 1850’s…
Soot and smoke from industrial
areas blackened nearby trees
 Dark moths became less visible
and pale moths stood out and
became easy prey
 More dark moths survived and
produced more dark offspring
 Population changed from mostly
light-colored moths to mostly
dark-colored moths
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
Adaptations to Habitat
 Arctic
– white fur in winter
camouflage from
• (structural adaptation)
Adaptations to Habitat
 Monkey-
– Grasping tail acts as
an extra hand to aid
movement through
• (structural adaptation)
Adaptations to Habitat
 Cactus
– Waxy skin reduces water
loss from evaporation
• (structural adaptation)
Adaptations to Habitat
 Black
– Hibernates to adapt to
seasonal changes
• (behavioral adaptation)
Artificial Selection
The breeding of organisms for desired
characteristics is called selective
 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?
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?
 Isolation
or complete separation occurs
 Over time new traits are developed
 Formation
in 3 steps:
of a new species can happen
1. Separation
portion of a population
becomes isolated from the
rest of the population by:
– newly formed canyon,
mountain range, lake
2. Adaptation
 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
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:
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
– Portion of a population becomes isolated from the rest of the
population by:
• Newly formed canyon
• Mountain range
• Lake
– As environment changes, separated groups adapt to their
new environment
– Groups of a population become so different they can no
longer interbreed
• Different species form
Biological Evidence of
Evidence for Evolution
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
 Homologous
Homologous structures
structures are
body parts of
organisms that
are similar in
structure and
position but
different in
 Suggests a
common ancestor
Evidence for common ancestry
 Body
parts that
perform a similar
function but
in structure are
Evidence for common ancestry
Remnants of hind-limb
bones are embedded inside
the whale’s body
Vestigial Structures
are body parts that
have lost their original
function through
– Human Tail Bone
– Appendix
– Tonsils
– Wisdom teeth
Comparing DNA
 Looking
at similarities
in DNA
 Human
chimpanzee DNA 99%
 Suggests
How are these species alike?
 Turtle
 Chicken
 Rat
Early development
Early development
 All
have a tail
 All have gill slits
 They share a common ancestor
Similar appearance
early in embryonic
The science of the
development of
embryos from
fertilization to birth is
called embryology
Suggest common