Evolution Notes: Natural Selection Types

Announcement : Quiz on WEDNESDAY!!! Covers:  Darwin  Processes (embryology, vestigial, mimicry, etc)  Selection Types (directional, stabilizing, etc.)

Stabilizing Selection Natural selection where the “average” individuals have a better chance of survival Different sized spiders  Big spiders get eaten  Small spiders can’t find food Students  Not serious students get demoted  Really smart students transfer The Average Wins

Directional Selection Natural selection where “extreme” individuals have a better chance of survival Woodpecker  Bugs are deep in a tree  Woodpeckers with longer beaks can reach them to eat Basketball  The basketball rim is pretty high  The tall players can score more points The ones with extreme traits win

Disruptive Selection Natural selection where extreme characteristics have a better chance for survival, but at the same time the average is harmed Snails  Snails come in three shades: dark, medium, light  On light and dark rocks the “extreme” snails survive, allowing the medium snails to get eaten The extreme wins while the medium loses

Natural Selection and Evolution If given enough time (millions of years) each type of selection can lead to the evolution of a species  For example: Birds with really long beaks to eat bugs in the tree! New species of snails that can camouflage in light and dark colored rocks!

Selection Types 5 Q’s What 3 things need to occur for Natural Selection? (hint: survival…..) What type of structure suggests that snakes used to have legs? (homologous, analogous, vestigial) Which type of selection favors the middle (average) trait? Which type of selection favors the extreme and harms the middle? Which type of selection favors the extreme?