What has caused SUPERBUGS (antibiotic resistant bacteria) like MRSA? 8-5 Notes: Natural Selection What has caused SUPERBUGS (antibiotic resistant bacteria) like MRSA?

how did organisms become so well adapted to their environment? What has caused the great diversity of life?

DARWIN’S EXPLANATION Darwin proposed that animals evolved to fit their environments.

Darwin realized that animals have many offspring and some don’t survive. The survivors are better suited to their environment.

HE CALLED THIS PROCESS…. Natural Selection

Darwin said that in nature, the environment creates selective pressure Natural Selection Mechanism by which EVOLUTION occurs The environment is the selective agent Darwin said that in nature, the environment creates selective pressure

Steps of Natural Selection Overproduction -organisms have many offspring, but not all will survive.

2. Genetic Variation Individuals vary within a population New traits appear due to genetic mutations

3. Struggle to Survive Organisms compete for resources (food, water, shelter, and mates) or get away from predators Some adaptations allow organisms to survive at a higher rate

4. Differential Reproduction (Descent with Modification) Organisms with the best adaptations will survive and reproduce passing these beneficial traits down to their offspring

Natural Selection Natural Selection acts on inherited traits or behaviors As environment changes, different traits will become beneficial.

Artificial Selection Humans breed for specific traits causing differences in species (i.e. dog breeding)

Insects become resistant to insecticides. Examples of Natural Selection Insects become resistant to insecticides. 1. Insecticide kills off most insects.

2. Those insects that survive have a gene that makes them resistant.

3. Resistant insects reproduce with other resistant insects.

4. Their offspring have the resistant gene 4. Their offspring have the resistant gene. Insecticides don’t work very well over time!

Other examples of evolution: Bacteria become resistant to antibiotics Don’t take antibiotics unless you have a bacteria infection!

MRSA

Peppered Moths in England There were more light moths (on light trees) before 1850. There were more dark moths (on dark trees) after 1850.

Pocket mice http://www.hhmi.org/biointeractive/making-fittest-natural- selection-and-adaptation