1. KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.

2. Several key insights led to Darwin’s idea for natural selection.
Darwin noticed a lot of variation in domesticated plants and animals.
Artificial selection is the process by which humans select traits through breeding.
neck feathers
crop
tail feathers

3. Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.
Heritability is the ability of a trait to be passed down.
There is a struggle for survival due to overpopulation and limited resources.
Fitness is a measure of the ability to survive and produce more offspring than fellow population members.
Darwin proposed that adaptations arose over many generations.

4. Natural selection explains how evolution can occur.
There are four main principles to the theory of natural selection.
variation
overproduction
adaptation
descent with modification
ADAPTATION
OVERPRODUCTION
DESCENT with MODIFICATION
VARIATION

5. Variation
The heritable differences that exist in every population are the basis for natural selection.

6. Overproduction
Having many offspring increases the chances for survival but also may cause competition for resources.

7. ADAPTATION
A certain variation that allows an individual to survive better than other individuals it competes against.

8. Descent with modification
Heritability of adaptations. More individuals will have the trait in every following generation as long as environmental conditions remain favorable for that trait.

9. Natural selection acts on existing variation.
Natural selection can act only on traits that already exist.
Structures take on new functions in addition to their original function.
wrist bone
five digits