Natural Selectionand Evolution!

Why two types of clover?

• What advantages does the striped clover have? The plain?

• How does cyanide help/hurt these plants in different habitats?

Organisms have variation

• Same species (Trifolium repens), different characteristics

• Variation = differences among individuals of one species; different forms of same trait (ex: eye colors)

Variation helps organisms adapt

• Adaptation = inherited characteristic, increases an organism’s chance for survival

• Fitness = ability of an individual to survive and reproduce in its environment

•Which clover is more “fit?” Why?

Variation allows for Selection

• Humans and nature “choose” which organisms win and get to procreate

• Artificial selection = human select most useful variations, allow those to reproduce

• ex: race horses - what trait would be selected for?

• ex: broccoli and other veggie friends

The struggle for existence

• Resources are limited, so only some can survive

• Natural Selection = individuals better adapted to their environment survive, reproduce, and pass on their genes

• AKA “survival of the fittest”

• leads to change over time (EVOLUTION!)

Natural Selection - Ex: Darwin’s Finches

Beak size and shape vary - all descended from common ancestor but changed over time

Evolution by Natural Selection

• Descent with modification = over time, natural selection produces organisms with differences from their ancestors

• Different food sources, habitats, body parts, behaviors

• Implies that living things are all related, have a common ancestor (common descent)

Common Descent - one ancestor in the past

Phylogenetic tree - distance between organisms is directly related to differences in genes (short distance = few differences, long = many)