1. Aim: How does evolution occur by natural selection?

2. How Does Evolution Occur?
EVOLUTION is a slow change in a species over time.
Evolution occurs by a process called NATURAL SELECTION.
Read this cartoon, what do you think NATURAL SELECTION is?

3. Considered the “father” of evolution.
Darwin
Considered the “father” of evolution.
Charles Darwin traveled to the Galapagos island, an uninhabited environment, where he studied evolution (Darwin’s Finches)

4. Darwin’s Theory of Evolution
Natural Selection:
Individuals with favorable traits are able to survive and reproduce.
Nature controls which traits are favorable.

5. Natural Selection NATURAL SELECTION is the KEY to Darwin’s theory.
According to this theory, evolution is controlled by NATURE.
Only the organisms that are able to SURVIVE and REPRODUCE will pass on their genes.

6. Natural Selection vs. Artificial Selection
Environment selects the desirable traits
that will appear in
the offspring.
People select the desirable traits that will appear in the
offspring.

7. Mechanisms of Evolution:
Overproduction
Variation
Natural Selection:
Struggle For Survival
Best Adapted To Survive
Darwin did NOT have knowledge of the genetic basis of inheritance

8. Overproduction More offspring are produced than can survive.
Overproduction leads to “Struggle for Existence” or Competition.
Compete for limited resources (food, water and shelter).
Only certain individuals are able to survive and reproduce.

9. Overproduction leads to
More offspring are produced than can survive (most die young).
Overproduction leads to
COMPETITION!!
Organisms such as bacteria, fish, insects, and rabbits have high repro-ductive rates because the chance that their young will survive is minimal.

10. Variation
Variation: Individuals of the same species have differences in their appearance, structure, or genes.
Increases the chance that some members of a species will survive an environmental change.

11. Sources of Variation - Sexual Reproduction (sperm + egg)=
- Meiosis (Independent Assortment. & Crossing Over)
- Mutation (Change in DNA)

12. Mutations change the base sequence of DNA Therefore Protein is changed
Most mutations are HARMFUL, but some can help the organism SURVIVE.

13. Adaptive Value
Adaptive Value: a change that produces a trait that helps an organism survive.
Ex: Camouflage
If all the members of a species were the same then an environmental change could wipe out the entire species.
VARIATION increases the chance that some members of a species will survive.

14. Best Adapted To Survive
Natural Selection
The ENVIRONMENT ‘chooses’ which traits have adaptive value.
Organisms with favorable traits in a certain environment will live to reproduce and pass on those traits, others will die out.

15. Struggle For Survival “Survival of the fittest”
“Only those BEST suited will survive because of competition for finite (limited) resources (oxygen, water, food, and shelter)

16. Conditions that lead to Evolution:
Using what you have learned:
Summarize evolution using the words:
Overproduction, Variation, Natural Selection, adapt to environment

17. Patterns Of Change
Species with SHORT reproductive cycles that produce MANY offspring tend to evolve more quickly than species with LONG life spans and FEW offspring.
Types:
Gradualism – evolution occurs steadily through time (Slow & Continuous) .
Punctuated Equilibrium- species stay the same for long periods of time and then change rapidly.
No Change
No Change
No Change

18. Extinction The disappearance of an entire species (ex. Dinosaurs)
It can be caused by temperature changes, pollution, or landscape changes.