1. Evolution: Natural Selection

2. Natural Selection: The Mechanism for Evolution
Definition: Process by which organisms that are best suited to their environment survive and reproduce most effectively
A mechanism that works in nature as artificial selection works with the aid of humans
What is artificial selection?
How are they similar? Different?

3. Natural Selection: How Does it Work?
1. Organisms produce more offspring than their environment can support
Struggle for existence
Many individuals die due to: disease, starvation, predation, etc.
Only some individuals survive to reproduce
Examples??

4. Natural Selection: How Does it Work?
2. There is variation within populations
Many variations are inherited
Some variations are favorable
Adaptation: a heritable characteristic that increases the ability of an organism to survive and reproduce
Examples??
Camouflage
Antibiotic or pesticide resistance
Mimicry
Behavioral

5. Natural Selection: How Does it Work?
3. Fitness: those individuals with favorable variations survive and reproduce
These variations are inherited (and passed on to offspring)
Therefore, offspring will also have these variations
??What could happen if the environmental conditions that favor these traits were to change??
4. Over long periods of time, genetic changes can accumulate
Evolution: The change in genetic frequencies in a population over time
Punctuated Equilibrium theory (Steven Jay Gould)
Doesn’t always take as long as Darwin originally thought (examples??)

6. EXAMPLES OF ADAPTATIONS

7. Types of Natural Selection
1. Directional Selection: Population moves to one extreme
2. Stabilizing Selection: Population moves to the middle
3. Disruptive Selection: Moves away from middle to both extremes