|Principle|Description|Example| |---|---|---| |Variation|Individuals within a population have many heritable variations.|The peppered moth comes in both light and dark colored variations.| |Inheritance|Many variations can be passed on from parents to offspring.|The dark color of the peppered moth is a heritable trait.| |Struggle for Existence|Organisms compete for resources.|Peppered moths compete for food and avoid predators.| |Differential Survival and Reproduction|Traits that enhance survival and reproduction are more likely to be passed on.|Dark colored peppered moths were better at surviving and reproducing in a polluted environment.| |Mode of Selection|Description|Example| |---|---|---| |Directional Selection|Favors one extreme of a trait.|Over time, the peppered moth population shifted towards dark colored moths.| |Stabilizing Selection|Favors the middle range of a trait.|Human birth weight tends to be around the middleweight range for better survival.| |Disruptive Selection|Favors extreme traits at both ends of the spectrum.|In a lake full of daphnia, some became smaller and less susceptible to parasites while others became larger but more susceptible.| |Sexual Selection|Selection based on traits that increase mating success.|The peacock's tail is a classic example of sexual selection.| |Type of Selection|Description|Example| |---|---|---| |Artificial Selection|Humans select for desired traits in plants and animals.|Breeders selected for specific traits in dogs, resulting in many different breeds.|