1. Natural Selection
For thousands of years humans have controlled changes in different species.
The wide variety of breeds
comes from humans carefully
crossing dogs with desired
traits to make the traits more
distinct (easily seen).

2. Selective Breeding
Humans do the same kind of “selection” with plants such as corn. Cross pollinating only corn with nice big kernels.
The practice by which humans select plants or animals for breeding based on desired traits is called selective breeding.

3. Charles Darwin

4. Darwin’s Thinking
Darwin knew that all populations are limited by starvation, competition, disease, and predation.
Only a limited number of individuals live to reproduce. These individuals must have traits to help them survive.
Some of these traits, Darwin reasoned, would be passed on to their offspring.

5. Adaptation
The shapes of the different finch beaks were adapted to the way each finch gets food.

6. Darwin’s Explains Natural Section
Natural selection is the mechanism, or process, by which organisms that are better adapted to their environment survive and reproduce more successfully than less well adapted organisms do.
The process of natural selection has four steps.

7. 1. Overproduction All species tend to produce more offspring than can survive.
2. Inherited Variation Within a population are many individuals, each with a slightly unique set of traits.
Today we know that variation is due to genetic differences, and that these genes are passed from parent to offspring.

8. 3. Struggle to Survive There are limited amounts of resources for each individual, as well as diseases and predators.
4. Successful Reproduction Individuals with the best traits for their environment survive to have more offspring than individuals with less favorable traits.

9. Extinction
Extinction occurs when the adaptations of a species are insufficient for survival in a changing environment.

10. Quiz How have humans controlled the traits of animals and plants?
What determines the traits of organisms in the wild?

11. Quiz Cont. Who created the theory of natural selection?
What is natural selection?

12. Quiz Cont. What is an adaptation?
What are the 4 steps of natural selection?
What happens when the adaptations of a species are insufficient for survival in a changing environment?