Download Chapter 2 Lesson 3 Change Over Time

Change Over Time
Dramatic changes have occurred
on Earth over time
Climates have changed, forests have
become deserts, and seas have dried up.
These changes affect the organisms within
these environments. Organisms must
respond to changes in order to survive.
Charles Darwin
In the 1800s, Charles Darwin
developed a theory about how
organisms change over time.
He studied different
populations of organisms.
Population
A population is all of the members of a
single species living in the same
geographic area.
Darwin
Charles Darwin studied different
populations of organisms.
Darwin noticed variations within the
populations.
He did not understand how these variations
occur.
Today, scientists know that variations result
from changes in an organism’s genetic
material.
Variations
Variations are differences among
members of the same species.
Natural Selection
Natural Selection is Darwin’s theory.
It states that an organism with favorable
variations is well suited to its environment.
It is more likely to survive and reproduce
than other organisms. These variations will
be passed on to the next generation. Over
time, the offspring of individuals with
favorable variations make up a greater
percentage of a population.
Natural Selection
Darwin’s theory is sometimes known
as “survival of the fittest” because the
organisms with the most favorable
traits survive.
What causes variations?
Changes in an organism’s
genetic makeup.
An organism that has changed
over time…
 Horses have changed over time. Ancestors of
horses walked on several spread-out toes that
probably helped the animals move through
swamps and mud.
 Once land dried, the horses also changed. They
developed single hooves that better suited the
horses to run on hard ground. This helped them be
able to run fast and escape predators.
Extinct
An extinct species no longer exists
anywhere on Earth.
Species become extinct because they
cannot adapt.
How does natural selection explain
how organisms change over time?
Organisms with the favorable variations are
better suited for survival and are more likely
to reproduce and pass on those traits to
their offspring. Over time, the organisms
with the favorable variation make up a
greater percentage of the population,
possibly resulting in a new species.
A few bacteria in a population are
resistant to an antibiotic. Explain how
this bacteria population might change
over time.
The bacteria that are resistant to the
antibiotic will reproduce and pass on this
resistant trait to their offspring. Eventually
the population of bacteria will consist of the
antibiotic resistant bacteria.
What are fossils?
Fossils are the remains, traces, or
imprints of organisms that lived long
ago.
Fossils
Organisms generally decay quickly after they
die.
Sediment can sometimes quickly cover an
organism soon after it dies and the hard parts
(skull, bones, teeth, shell, etc…) of the
organism will be preserved.
These hard parts can become fossils.
Minerals in the sediment replace the hard body
parts and the surrounding sediment along with
the body harden into rock.
A fossil forms.
Fossils
Insects can become trapped in tree
sap.
The tree sap will harden into amber
and this preserves the insect creating
a fossil.
Fossil Formation
Imprints, like an animals footprint, are
made when animals walk across wet
soil. If a footprint is covered quickly by
sediment, the footprint can be
preserved.