Transcript Section 1 Change over Time

Bell Work
• In 3-5 sentences journal about the different adaptations that
these finches have and how do they help them survive?
Section 1
Change over Time
Objectives
• Identify two kinds of
evidence that show that
organisms have changed
over time.
• A characteristic that
helps an organism
survive and
reproduce in its
environment is called
an adaptation.
2 kinds of evidence
• Some adaptations are
physical, such as fur or
scales. Other adaptations
are behaviors that help an
organism find food, protect
itself, or reproduce.
• Individual organisms that share
the same characteristics might be
members of the same species.
• A species is a group of organisms
that can mate with one another to
produce fertile offspring.
• Groups of individuals of the same
species living in the same place
make up a population.
Do Species Change over Time?
• Since life first appeared,
many species have died
out, and many new
species have appeared.
• Scientists observe that
the inherited
characteristics in
populations change over
time. Scientists think
that as populations
change over time, new
species form.
Objectives
• Explain how comparing
organisms can provide
evidence that they have
ancestors in common.
Comparing Skeletal Structures
• The structure and order of
bones of a human arm are
similar to those of the front
limbs of a cat, a dolphin, and
a bat.
• These similarities suggest that
cats, dolphins, bats, and
humans had a common
ancestor.
Comparing DNA
Molecules
• Scientists also compare
organisms at the molecular level.
• Species that have more DNA in
common are more closely related
and have shared a common
ancestor more recently.
• The fact that all existing
species have DNA
supports the theory that
all species share a
common ancestor.
Section 2
•How Do Population
Changes Happen?
Objective
• Describe the four parts
of Charles Darwin’s
process of natural
selection.
• Natural selection is the
process by which
organisms that are better
adapted to their
environment survive and
reproduce more
successfully than less well
adapted organisms do.
Darwin’s Theory of Natural
Selection
• In 1859, Darwin published a
famous book called On the Origin
of Species by Means of Natural
Selection. In his book, Darwin
proposed the theory that change
in populations happens through
natural selection.
• Section 3
Natural Selection in
Action
Objectives
• Give two examples of
how natural selection can
result in an adaptation
that helps an organism
survive.
Changes in Populations
• The theory of natural
selection explains how a
population changes in
response to its
environment. Well-adapted
individuals will likely
survive and reproduce.
• Examples:Scientists think that
hunting in Uganda is affecting
elephant population. Because
ivory is very valuable, elephants
are hunted for their tusks. So,
fewer tusked elephants survive to
reproduce, and more tuskless
elephants survive. Tuskless
elephants pass the tuskless trait to
their offspring.
• Examples:An insecticide
kills all but a few insects in
a population. The
survivors have a gene that
makes them immune. They
pass it to their offspring
and after a few generations,
the population is mostly all
immune.
Forming a New Species
• Sometimes, drastic changes that
can form a new species takes
place. A new species may form
after a group becomes separated
from the original population.
The formation of a new species
as a result of change over time is
called speciation.
Objectives
• Outline the process of
speciation.
• Speciation often begins when a part
of a population becomes separated
from the rest. Populations constantly
undergo natural selection. After two
groups have separated, natural
selection continues to act on the
groups. If the environmental
conditions for each group differ, the
groups’ adaptations will differ.
• Over generations, two separated
groups of a population may become
very different through natural
selection due to the division. Even if
a geological barrier is removed and
the groups are reunited, they may no
longer be able to interbreed. If they
cannot interbreed, the two groups
are no longer the same species.