1. Mechanisms of Evolution What causes organisms to change over time?

2. What is Evolution? Biological Evolution is descent with modification. This definition includes: Small-scale evolution-changes in a population from one generation to the next. Large-scale evolution- descent of different species from a common ancestor over many generations.

3. What is evolution? Evolution is not just change over time, it must include the passing of genetic traits.

4. Mechanisms of Evolution There are four main processes that are considered the basic mechanisms of evolutionary change. 1. Mutation 2. Migration 3. Genetic Drift 4. Natural Selction

5. Mutation A mutation is a change in DNA sequence caused by an error in replication or repair Example: a mutation could cause parents with bright green coloration to have offspring with a gene for brown coloration. This would make the genes for brown beetles more frequent in the population.

6. Migration Migration is the movement of individuals from one population to another. Example: If some individuals from a population of brown beetles joined a population of green beetles, that would make the genes for brown beetles more frequent in the green beetle population.

7. Genetic Drift Genetic drift refers to chance changes in the genetic makeup of a population from one generation to the next. Example: Imagine that in one generation, two brown beetles happened to have four offspring that survived to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation – but just by chance.

8. Genetic Drift

9. Natural Selection Natural Selection is a process in which some individuals have genetically based traits that improve their chances to survive and reproduce, and thus have more offspring surviving to reproductive age.

10. Natural Selection Try to create your own scenario using our brown and green beetle populations that displays how natural selection works!

11. Natural Selection Let’s imagine Natural Selection taking place in our beetle population: 1. There must be variation in traits. For this example, some are green and some are brown. 2. There is differential reproduction. The environment cannot support unlimited population growth, so not all individuals can have offspring. In our example, green beetles tend to be eaten by birds and survive to reproduce less often than brown beetles.

12. Natural Selection 3. There is heredity. The surviving brown beetles have brown beetle babies because the trait is genetically determined. 4. In the end, the trait that allows more beetles to survive and reproduce ( in this case brown coloration) becomes more common in the population.

13. Natural Selection What will happen to the population if this process continues?

14. Image Credit All images obtained from: University of California Museum of Paleontology's Understanding Evolution (http://evolution.berkeley.edu).