1. Darwin & Natural Selection
Evolution Unit

2. Learning Goals 1. Define "Evolution" & "Natural Selection".
2. Describe the 4 steps of Natural Selection, giving an example of each.
3. Explain the importance of "Variation".
4. Explain how environmental changes can trigger evolution

3. Theory of Evolution Evolution: The process of change over time
Specifically, a change in the frequency of a gene or allele in a population over time (it’s all about the DNA!)

4. Evolution vs. Natural Selection
They are not the same thing!
Evolution – is the “what” (organisms changing over time)
Natural Selection is the “how” (the mechanism that causes the changes)

5. Charles Darwin Father of Evolution
Darwin went on a 5-year trip around the world on the ship, the HMS Beagle
As the ship’s naturalist, he made observations of organisms in South America and the Galapagos Islands

6. What did Darwin’s travels reveal?
The diversity of living species was far greater than anyone had previously known!!
Species separated on different islands, while similar, had different traits

7. How did tortoises and birds differ among the islands of the Galapagos?
Each island had its own type of tortoises and birds that were clearly different from other islands

8. Galapagos
Tortoises

9. Darwin’s Travels
These observations led him to develop the theory of evolution!!
He proposed that natural selection was the mechanism for evolution
He wrote a book called “The Origin of Species”

10. Natural Selection
Organisms that inherit advantageous traits will reproduce more successfully

11. 4 Steps of Natural Selection
Darwin’s Theory of Natural Selection occurs in four steps:
Overproduction
Genetic Variation
Competition
Selection

12. 1. Overproduction
Each species produces more offspring than can survive
Only some will survive to grow up and reproduce (passing on their genes)

13. 2. Genetic Variation
Each individual has a unique combination of inherited traits (in the DNA/genes).
If an organism has a trait that helps it survive and reproduce, we call it an adaptation

14. What adaptations do you see?

15. What adaptations do you see?

16. Why is Variation Important?
Because the environment changes.
The more variation within a species, the more likely the species will survive
If everyone is the same, they are ALL vulnerable to the same environmental changes or diseases
Organisms that cannot evolve to adapt to a changing environment, will become extinct.

17. 3. Competition Individuals COMPETE for limited resources:
Food, water, space, mates
Natural selection occurs through “Survival of the Fittest”
Fitness: the ability to survive and reproduce
Not all individuals survive to adulthood
Starvation, sickness, eaten by predators

18. “Survival of the Fittest”
It’s not always the biggest, or the strongest, or the fastest, or the smartest!
It’s simply the one that is best able to survive in the environment

19. 4. Selection
The individuals with the best traits / adaptations will survive and have the opportunity to pass on their traits to offspring.
Those traits will increase in the population

20. 4. Selection
The individuals that do not survive will not pass on their traits.
Those traits will decline (go down) or disappear in the population

21. Selection
Individuals with traits that are not well suited to their environment either die or have fewer offspring.
Evolution occurs when successful traits build up in a population over many generations and unsuccessful traits are eliminated by the death of the individuals.
The successful traits have been “selected” ✔ ✗

22. Gene Pool
The gene pool is all of the different traits in the population

23. Gene Pool
The gene pool will change as some traits are added (through mutation), successful traits increase, and unsuccessful traits decrease

24. What natural selection is NOT
It is NOT a change during an organism’s lifetime
It is caused by the traits that an organism is born with…found in the genes/DNA
It is NOT a conscious act
Organisms do not “try” to adapt. They only try to survive and reproduce!
It is NOT random chance
There are traits that are more likely to get passed on, because they are the best fit for the environment

25. Peppered Moths
A famous example of an environmental change causing evolution
Click here to watch a Youtube clip:

26. Peppered Moth A
Which moth will the bird catch? B

27. Learning Goals 1. Define "Evolution" & "Natural Selection".
2. Describe the 4 steps of Natural Selection, giving an example of each.
3. Explain the importance of "Variation".
4. Explain how environmental changes can cause evolution