Life Science 7A
Notes Chapter 4-1
What is Evolution?
Evolution- is a changing in organisms over time.
 Fossils show that the original life on earth was very simple one-celled
organisms.
 New species evolve from previous organisms.
Adaptations are traits in an organism that allow it to survive in its environment.
 Ex. Heavy fur on a polar bear, modified leaves.
If a change occurs in an organism’s genes a mutation may appear.
 Most mutations cause death like cancer.
 Some mutations become helpful in survival and become adaptations.
Life Science 7A
Notes 4-2
What are Fossils?
Scientists are very interested in how an animal becomes extinct, or no longer
found on earth.
Some extinct organisms leave imprints or remains behind, that scientists can study
to learn about them.
 These are fossils.
 Fossils give scientists a look at organisms from long ago.
Types of Fossils:
A) Organisms in ice
B) Amber is tree sap that has hardened to stone sometimes having an
organism in it.
C) Sedimentary rocks can have fossils if the remains of an organism are
quickly covered over by sediment before they can decay.
a. Pressure from sediments on top of the sediment eventually
change the sediments to rock.
Life Science 7A
Notes 4-3
What is the Evidence That Supports Evolution?
Scientists use the fossil record to trace adaptations in organisms that have lead to
evolution.
Dinosaurs underwent a mass extinction- many species dying in a short period of
time.
 This allowed the mammals, which were better-adapted animal for the
earth’s colder climate, to become the dominant animal on earth.
 Scientists have traced the modern day horse back to an animal that
was somewhat dog-like called Eohippus.
Scientists often look at similar body structures called homologous structures.
- The more similar the structures the more closely related the
organisms.
- Ex. Bat’s wing, Human hand
Scientists can get more accurate ages of fossils by using radioactive dating.
 This is a way of measuring radioactive decay of an element to
determine age.
 The more decay the older it must be.
 C-14 or carbon 14 is commonly used for this.
Life Science 7A
Notes 4-4
What is Natural Selection?
Jean Baptiste de Lamarck was one of the first scientists to develop a theory of
evolution.
- He believe organisms develop new characteristics to help them
adapt to their surroundings.
- He believed that giraffes probably had short necks at one time.
- His theory was proven wrong since he had little evidence to
support it.
Charles Darwin was a famous evolutionist who had the theory of why new species
develop.
He called this Natural Selection.
 This means that offspring will favorable traits are more likely to
survive and pass on those traits.
 This is also known as survival of the fittest.
Ideas to natural selection:
1)
2)
3)
4)
5)
Overproduction of offspring- the weaker offspring don’t survive.
Competition is the struggle for resources such as food, water and
sunlight.
Variation is a slight difference in organism’s traits. The big variations
are from mutations and may become adaptations.
Survival of the Fittest this is when only the best organisms live and
reproduce
Evolution of New Species favorable variations can be passed on to
form new and different species.
Life Science 7A
Notes 4-5
How does the environment affect natural selection?
All organisms have a certain amount of living space needed for them to survive.
- They must get the needs of life (water, food, mates) from their
living space.
- Members of a community compete for living space and
sometimes organisms don’t survive.
- Stronger animals will prey on weaker animals.
Humans can dramatically change organism’s living space.
- Some organisms have become extinct because of over hunting,
or building on their living space.
o Most of Florida was swamp marsh that was drained and
changed so man could live their.
-
Some organisms have learned to cope with humans.
o Ex. Black Bears and dumps
Pollution from humans has also caused changes in organisms.
- The industrial revolution in the early 1900’s produced so much
smoke and ash that white barked trees turned to grey.
- The Peppered moth changed to a grey color since they used to
hide on the white bark.
Extinction is the disappearance of members of a species.
- Dodos, Carrier Pigeons
- Endangered organisms are close to being extinct.
- There are many laws to protect endangered species such as the
grizzly bear and bald eagle.
Over fishing of the earth’s oceans has caused a great decline in the amount of fish.
- Netting fish can take too many out of the population.
- Fish catches around the world have been dropping due to the
overfishing.
Life Science 7A
Notes 4-6
How have humans changed over time?
In 1974, the oldest human-like fossil ever discovered was called Lucy.
- She was about 3.5 million years old.
- She was only 1meter tall, but walked upright.
Modern humans have not always been around on earth.
- Man evolved to later live in caves, make tools, and build fire.
The name of the modern human is Homo sapien.
- This is name means wise human due to the large brain.
- Neanderthals and Cro-Magnons lived before modern humans.
Anthropology is the study of human beings and their origins.