1. Populations Change Over Time through Natural Selection
Individuals in a population vary each generation.
Some of these variations are genetic, or inherited.
More individuals are produced to live than grow and reproduce.
Individuals with some genes are more likely to survive and reproduce than individuals with other genes.

2. Darwin and His Theory of Evolution by Natural Selection
Evolution- changes in the characteristics of groups of organisms over time
Charles Darwin was the first to propose a feasible mechanism for evolution. It is called natural selection. *

3. Evolution by Natural Selection is a theory. What is a scientific theory?
Scientific Theory- an idea that is strongly supported by evidence. It is generally accepted and used to explain many observations.
*Remember: The word “theory” in everyday language and in scientific language mean very different things.
In everyday language, people use the word theory to mean a hypothesis or an educated guess.

4. Natural Selection- differential success in survival and reproduction of individuals with different phenotypes (physical characteristics) resulting from interactions with their environments

5. Conditions Needed for Natural Selection: VISTA
Variation
There are a variety of forms of traits or phenotypes. *

6. Conditions Needed for Natural Selection: VISTA
2. Inheritance
Only traits that are determined by an organism’s genes will be passed to the next generation. *

7. What causes genetic variation?
1) Mutations- changes in the DNA sequence can result in new traits
 2) Sexual Reproduction- New combinations of traits can be created in gametes during meiosis.
The wide variety of gametes created will join together to make diverse offspring.

8. Conditions Needed for Natural Selection: VISTA
4. Survival and Reproduction
Individuals compete for limited resources, such as food, shelter, and mates.
Individuals with traits best adapted for the environment are able to out compete other individuals for resources, allowing them to survive and reproduce more. *

9. “Survival of the Fittest”
Evolutionary fitness isn’t a measure of physical fitness but of reproductive fitness.
Fitness- Relative ability to survive and produce offspring in an environment *

10. Conditions Needed for Natural Selection: VISTA
4) Time
Evolution occurs over generations.

11. Conditions Needed for Natural Selection: VISTA
5) Adaptations- an inherited characteristic that increases an organism’s chance of surviving and reproducing
Over time, natural selections causes adaptations to become more common in a population. *