Download Evolution #1

Evolution #1
Mrs. Cabak & Mrs. Osakwe
Campbell Middle School
Life Science - 7th Grade
Bell Ringer – Monday April 10, 2017
•How do fossils provide evidence
of change over time (which is
the definition of evolution?
Fossil
Trilobite
Seed Ferns
The remains or imprints of once-living organisms found in layers of rock are
called fossils. Fossils can be complete organisms, parts of organisms, or just a
set of footprints. Fossils usually form when a dead organism is covered by a
layer of sediment. Over time, more sediment settles on top of the organism.
Minerals in the sediment may seep into the organisms and gradually replace
the organism with stone. Fossils provide evidence of change.
Adaptation
• A characteristic that helps an organism
survive and reproduce in its environment
is called an adaptation. Adaptations may
be physical, such as a long neck or
striped fur. Or adaptations may be
behaviors that help an organism find
food, protect itself, or reproduce. An
alteration or adjustment in structure or
habits, often hereditary, by which a
species or individual improves its
condition in relationship to its
environment.
Bright colors =
poisonous
Brown colors=
camouflage
Ancestor
An ancestor is the actual or
hypothetical organism from
which later organisms evolved.
The fossil record provides evidence
about the order in which species
have existed. Scientists think that all
living species descended from
common ancestors. Evidence of
common
ancestors can be found in fossils
and in living organisms.
Evolution
Scientists observe that species have changed
over time. They also observe that the inherited
characteristics in populations change over time.
Scientists think that as populations change over
time, new species form. Thus, newer species
descend from older species. The process in
which populations gradually change over time is
called evolution as a result of natural selection
acting on the genetic variation among
individuals, and resulting in the development of
new species.
Extinction
Extinction occurs as a result of the dying out of species or population.
Some of the important divisions in the geologic time scale mark times
when rapid n changes happened on Earth. During these times, many
species died out completely, or became extinct. When a species is
extinct, it does not reappear.
Mass Extinction
At certain points in the Earth’s history, a large number of species disappeared
from the fossil record. These periods when many species suddenly become
extinct are called mass extinctions leading to a relatively sudden, global
decrease in the diversity of life-forms on Earth.
Scientists are not sure what caused each of the mass extinctions. Most
scientists think that the extinction of the dinosaurs happened because of
extreme changes in the climate on Earth. These changes could have resulted
from a giant meteorite hitting the Earth, or, forces within the Earth could have
caused many volcanoes and earthquakes.
Mutation
Mutations: Substitutions can accidentally happen in
DNA. Changes in the number, type, or order of bases on
a piece of DNA are known as mutations.
Do Mutations Matter? There are three possible
consequences to changes in DNA: an improved trait, no
change, or a harmful trait. Fortunately, cells make some
proteins that can detect errors in DNA. When an error is
found, it is usually fixed. But occasionally the repairs are
not accurate, and the mistakes become part of the
genetic message. If the mutation occurs in the sex cells,
the changed gene can be passed from one generation to
the next.
The original base
sequence on the top
has been changed to
illustrate
(a) a substitution,
(b) an insertion, and
(c) a deletion.
How Do Mutations Happen?
Mutations happen regularly because of random
errors when DNA is copied. In addition, damage to
DNA can be caused by abnormal things that happen
to cells. Any physical or chemical agent that can
cause a mutation in DNA is called a mutagen.
Examples of mutagens include high-energy
radiation from X rays and ultraviolet radiation.
Ultraviolet radiation is one type of energy in
sunlight. It is responsible for suntans and sunburns.
Other mutagens include asbestos and the chemicals
in cigarette smoke.
Acquired Trait
An acquired trait is a change in an individual organism's
structure or function that occurs during the lifetime of the
organism, caused by injury, disease, or environmental
factors, and that is not inherited by future generations. It is
not coded in the organism's DNA and is a product of the
environment's influence on the organism.
These traits can strongly influence the survival of an
organism. Acquired traits can cause an organism with a
genetic disadvantage to out-compete another. An example
of an acquired trait is a bodybuilder's large muscles. They
were acquired by lots of exercise and not genetics, so the
offspring of the body builder are no more likely to have
large muscles than other offspring. Since acquired traits
cannot be passed on to offspring, they do not increase the
fitness of a population, and natural selection does not
influence them.
Analogous structure
• Comparing Skeletal Structures: What do your arm, the front leg of a cat, the
front flipper of a dolphin, and the wing of a bat have in common? You might
notice that these structures do not look alike and are not used in the same way. –
they are analogous structures. But under the surface, they have similarities. 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. Over millions of years, changes
occurred in the limb bones. Eventually, the bones performed different functions
in each type of animal.
Mold
•A mold is a hollow area
formed when a fossilized
organisms that was
buried in sediment
dissolves.
Cast
Fossils sometimes form when a dead organism
is covered by a layer of sediment. The
sediment may later be pressed together to
form sedimentary rock. Fossils can form in
sedimentary rock. The most common way is
when an organism dies and becomes buried in
sediment. The organism gradually
decomposes and leaves a hollow impression,
or mold, in the sediment. Over time, the mold
fills with sediment which forms a cast of the
organism. A cast is a fossil that is a copy of the
organisms shape.
CLOSING:
Think-Pair-Share
Tell your partner:
3 new things you learned today
2 things you knew before
1 question you still have about evolution