The Theory of Natural Selection

Artificial Selection Humans created diversity choosing specific traits to breed Dogs, Crops, Livestock Humans selected (not naturally) traits thought to be advantageous Only inheritable traits can be passed down Importance: Shows life can change over a period of time

Dog traits have been selected by breeders for centuries to produce various breeds.

Natural Selection With adaptation Without adaptation Four factors: Overpopulation: more offspring are born than can survive Variation: individuals of a population have differences. Some variations allow a better chance of survival (Adaptations) 3)Struggle for Survival: Because of limited resources, organisms compete against each other for survival. 4) Descent w/ modification: Those with advantages will reproduce and make more of the population

The Myth

Which rabbit is best adapted to this environment? Over time, those not adapted most likely die…that’s natural selection!

Which rabbit is best adapted? Do the dark rabbits turn white? No! They get eaten.

Struggle for Survival Populations do not grow unchecked Limiting Factors: food, water, shelter, disease, predators Fitness: measure of the ability to survive & produce more offspring

New environments are continally created New environments are continally created. Life adapts with the changing conditions.

Changing Environments Evidence of a changing Earth Marine fossils atop mountains Dry valleys with ocean fossils Rivers create canyons As environments changed… Those with adaptation: more likely to survive & reproduce Those without adaptation: more likely to perish

Natural Selection in Action: The Peppered Moth Analysis Before the industrial revolution, the trees in the forest around Manchester, England were a light grey/green due to the color of lichens (fungus) on their trunks. Peppered moths, or Biston betularia, which lived in the area, were mostly lightly colored with dark spots. However, there was some color variation between the moths. The most common moth color was light with dark spots and the least common were dark with light spots. Because there were not enough resources to support the entire population, the members of this species had to compete for survival. Their coloring, when against a similar background, served as camouflage against predators such as birds and lizards, thus increasing chances of survival.

Natural Selection in Action: The Peppered Moth Analysis As the Industrial Revolution progressed, the trees became covered with sulfur dioxide, turning the trunks dark.

Review Quiz What is artificial selection? What is natural selection? How does natural selection lead to population changes? Explain why scientists believe the Earth’s environments have been changing for millions of years. Why don’t populations (such as deer) continue to grow unchecked?