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Think about it…
Open your manuals to page 112.
Describe the fossil record of your own life that might
be found 65 million years from now.
What items, or artifacts, might be likely to survive?
What kinds of things would decay and disappear?
Do you think your fossil record would produce an
accurate picture of your life?
What might be missing?
Change over Time and how
Population Changes Happen
State Standard:
SPI 5.3- Analyze data on levels of variation
within a population to make predictions about
survival under particular environmental
conditions.
Changes over time
● For thousands of years, people have
observed change in living things over
time.
● The fossil record shows organisms
developing new traits & losing others.
● Therefore - as populations change over
time, new species may form. Thus,
newer species descend from older
species
Fossils
● Fossils are the imprints or remains of
once-living things often preserved in
sedimentary rocks.
● They help us unravel the past
● Fossils can suggest the
climate of a region at
the time of the fossil.
● Different fossils will be found in
different sediment layers and/or
different regions.
Older fossils will
be in the bottom
layers.
Fossil
Fossil
Fossil
The Fossil Record
● By studying fossils, scientists have
made a timeline of life known as
the fossil record.
● The fossil record organizes fossils
by their estimated ages and
physical similarities.
● Comparing organisms in the fossil
record can reveal how organisms
have changed over time.
Evidence of Ancestry
● Evidence of common ancestors can be
found in fossils and in living organisms.
Many species have common physical
features.
● The human arm, whale flipper, horse
leg and bird wing all have the same bone
shape, suggesting a common ancestor.
● This is called a homologous structure.
● Embryo’s (organisms at an early stage of
development) also support the idea of
common ancestry because of a similar
look.
• Evidence that groups of organisms
have common ancestry can be found
by comparing the groups' DNA.
African wild
dog
Dhole
Ethiopian
wolf
Coyote
Gray
wolf
Dog
Golden
jackal
Black-backed
jackal
Side-striped
jackal
Which two species are most closely related?
2 answers possible.
Fig. 23-6, p. 491
Charles Darwin’s Theory
• As the naturalist–a scientist who
studies nature–on board the
British ship HMS Beagle, Darwin
made several observations that
shaped his theory.
● One noted observation was that all the
finches on the Galapagos island looked
about the same except for the shape of
their beak.
●This lead to a conclusion that all
the finches were descendants of
the same original population.
●The shape of the beaks were
adaptations for eating a particular
type of food (Ex. long beaks were
used for eating insects, short for
seeds)
● Darwin realized organisms best
matched to their environments are
more likely to survive & reproduce.
● Hence – Natural Selection
Genetics and Inherited Traits
● Darwin knew that organisms inherited
traits, but not how they inherit traits.
● He knew there was
great variation among organisms,
but not how that variation occurs.
● Today, we know that variation happens as a
result of the exchange of genetic
information as it is passed from parent to
offspring.
● The process called selection happens
when only organisms that carry these
genes can survive
to reproduce.
●A trait is a form of a
hereditary
characteristic.
● The practice by which humans select
plants or animals for breeding based on
desired traits is selective breeding.
Changes in Population
● Changes in population can occur when a
new force affects the survival of
individuals in the population.
● Darwin realized that any species can
produce many offspring. He also knew
that the populations of all species are
limited by starvation, disease,
competition, and predation.
● Only a limited number of individuals live
long enough to reproduce. Thus, the
survivors are special.
● Therefore - Darwin reasoned that the
offspring of the survivors inherit traits
that help the offspring survive in their
environment.
Example-Insecticide Resistance
Forming a New Species
● Sometimes, drastic changes can form a
new species.
● In the animal kingdom, a species is a
group of organisms that can mate with
each other to produce fertile offspring.
● A new species may form after a group
becomes separated from the original
population. This group forms a new
population.
● Over time, the new population
adapts to its new environment.
● the new population & the original
population differ so greatly that
they can no longer mate
successfully. The new population
may then be considered a new
species.
● The formation of a new species as a
result of change over time is called
speciation
Putting it together. . .
Complete the following skill sheet
to reinforce these concepts.