Fun fact: Your body releases odorless hormones called pheromones that can lead to sexual arousal, aggression and marking of territory.

Catalyst What are things that you find attractive in others (both physical and emotional)?

Symmetry

Natural Selection Types of selection: Sexual Directional Stabilizing Disruptive

Sexual Selection Organisms with traits that increase a chance of mating and passing down genes to offspring are more likely to survive.

Sexual Selection

Graph a “NORMAL” population.

Scenario 1: Leaves towards the bottom of trees are disappearing. Some giraffes can reach leaves higher up, while others’ necks are not long enough? Which giraffes will thrive? Which giraffes will die out? What will future generations look like?

Scenario 2: A certain species of rabbits in a dense forest come in brown and white fur colors. Hawks, soaring overhead, often eat the rabbits. Which rabbits will be easier to spot? Which color trait will more likely be passed on to future generations?

Directional Selection Individuals that display an “extreme” trait are selected for. Other individuals are selected against. Population shifts toward this trait, away from the opposite.

Scenario 3: Lizards range in size from tiny to very large. Small lizards generally run very slowly while large lizards are usually the easiest for predators to see? What size lizard stands the best chance of survival?

Scenario 4: Human babies of very low birth weight are often more prone to disease. Babies of very large weights are difficult for mothers to safely deliver. What size babies stand the best chance of survival?

Stabilizing Selection Individuals that display an average trait are selected for. Individuals that display extreme traits are selected against. Population shifts towards the average trait, and those with extreme forms die off.

Scenario 5: Limpets are marine animals that attach to rocks. Their color varies from pure white to dark brown. White-shelled that are on rocks covered with goose barnacles (also white) are at an advantage. On bare, dark-colored rocks, brown limpets are at an advantage. What “advantage” is being referred to above? If you were a dark limpet, where would you live? A white limpet? What color would have the hardest time surviving?

Disruptive Selection Individuals that display either extreme are selected for. “Average” individuals are selected against. Population shifts towards away from the average trait, towards BOTH extremes.

Assignment: Design an example situation (1 paragraph each) representing a type of selection we covered. Include the following: 1. Description of the animals involved and their traits 2. How is nature selecting for/against certain animals 3. Which trait will be come more common/less common and why? 4. Name the type of selection.