There are four types of natural selection: 1) Directional selection which favors an extreme variation of a trait, 2) Stabilizing selection which favors the average phenotype, 3) Disruptive selection which favors extreme traits while the average declines, and 4) Sexual selection which favors traits that increase success in finding a mate and reproducing. Examples are given for each type of selection.

1. Types of Natural Selection

2. Think. Pair. Share.
What are the driving
factors for the evolution
of a beetle from small and
brown to larger, red, and
spotted?

3. Types of Natural Selection

4. Types of Natural Selection

5. Types of Natural Selection

6. Types of Natural Selection

7. Types of Natural Selection

8. Types of Natural Selection

9. Types of Natural Selection
In some environments, a species may face one or
many selective pressures.

10. Types of Natural Selection
A selective pressure may increase or decrease the
survival and reproduction rate of certain traits.
Weed killer is a selective pressure.

11. Types of Natural Selection
New population
Why do they not die?

12. Types of Natural Selection
Evolution

13. Types of Natural Selection
Examples include climate, food availability, and
predators.

14. Types of Natural Selection
There are 4 types of Natural Selection:
1) Directional Selection
2) Stabilizing Selection
3) Disruptive Selection
4) Sexual Selection

15. Types of Natural Selection
Suppose a certain mouse population has a range
of fur colours, from light brown to dark brown.

16. Directional Selection
1) Directional selection occurs when a selective
pressure favours an extreme variation of a trait.

17. Directional Selection
For example, the surrounding woody environment may
provide better camouflage for darker mice, thus most
of the lighter colour mice may be easily hunted.

18. Stabilizing Selection
2) Stabilizing selection occurs when a selective
pressure favours the average phenotype.

19. Stabilizing Selection
For example, a new predator may only be able to see
vivid colours (like white and dark brown), allowing the
dull brown mouse to avoid detection and escape.

20. Disruptive Selection
3) Disruptive selection favours extreme traits for
survival while the average phenotype declines.

21. Disruptive Selection
For example, predators may not eat the vividly
coloured mice in the area because the other white and
dark brown creatures in the area are toxic.

22. Sexual Selection
4) Sexual selection favours traits that increase the
success for an organism to find a mate and reproduce.

23. Sexual Selection
Usually involves (female) mate choice or (male versus
male) competition.
Examples:
Peacock
Satyr tragopan (video)
Bighorn rams (video)

24. Sexual Selection
Sexual Dimorphism is the difference of phenotypes
between males and females of the same species.
These are the traits often used in sexual selection.
Examples include:
- Colour
- Height
- Size of a particular feature
(such as horns or tusks)

25. Sexual Selection
The satyr tragopan displays its blue horns and wattle
to attract females.