1. What is Evolution?
The change in DNA of a population over time.

2. Jean Lamarck's Theory Do you think this is really how it happened?
Long ago, giraffes had much shorter necks.
As food became scarce the giraffes would stretch their necks to reach leaves higher in the trees.
Over time, giraffes had longer necks from constant stretching.
Do you think this is really how it happened?

3. Charles Darwin Developed the theory of NATURAL SELECTION in 1838.
Father of evolution

4. What is Natural Selection?
It is the process by which individuals that are better suited to their environment survive and reproduce most successfully.
It is some times called survival of the fittest. Whoever “fits” the best into their environment is the one who will survive and reproduce.

5. Darwin's Theory
Just like people are all not the same height, not all giraffes were born with the same length neck. Some were born with longer necks.
As food became scarce, those with longer necks could reach food and survive, those with shorter necks starved and died.
Since only long neck giraffes were reproducing, eventually over time all giraffes came to have long necks.
Given enough change and time, new species could evolve.

6. Darwin's Theory
Over time, natural selection results in changes in the inherited characteristics of a population
His theory of natural selection includes:
1. Overproduction
2. Competition
3. Variation
4. Survival of the Fittest
5. Transmission of Favorable Variations
6. Evolution of Species

7. 3. Variation
Some individuals are better fitted to survive due to variations in their genes.
ie. Giraffe with long neck is better fitted that one with a short neck.

8. 4. Survival of the Fittest
Those individuals better fitted to their environment survive and are more likely to live long enough to reproduce.
Fitness is the ability to survive and reproduce in a given environment.

10. 5. Transmission of Favorable Variations
The offspring of the fittest individuals will inherit the favorable variations that enabled their parents to survive and reproduce.

11. 6. Evolution of Species
The accumulation of favorable variations will gradually lead to the appearance of new species better adapted to the environment.

12. Darwin’s only problem!!!
The only problem with Darwin’s Theory is that it did not explain how these “variations” arise.

13. Today’s Modern Theory of Evolution
The modern theory of evolution accepts the notion of natural selection and uses the present knowledge of genetics to explain how variations arise.

14. 1. Sources of Variation 1. Random Mutations 2. Crossing-over
(during meiosis)

15. Natural Selection
Traits that increase an organism’s chances of survival and reproduction are passed on and eventually increase in frequency.

17. Review What is natural selection? Explain variation.
What are 2 sources of variation?
What is the objective of natural selection?

18. Exit Ticket
On a blank sheet of paper, use what you learned in class to answer the following questions based on the cartoon to the right.
Explain Darwin’s theory
According to Darwin’s theory why did the Wainwrights not survive?
According to Darwin’s theory, why did Bobby’s family survive?