Natural Selection A Big Idea! (new handout is page 27 ½)

Resources: stuff that is in the environment that is needed for survival often limited (can be used up)

environment air food mate shelter organism

Competition: The effort of 2 or more organisms acting independently to get resources that are in short supply.

Variation: Differences in shape, structure, or function Caused by sexual reproduction or mutation Dangling earlobeAttached earlobe

Adaptation: A useful trait that helps an organism to survive, and which gives it an advantage in its environment. camouflage

Overpopulation: Too many organisms in one environment Can lead to competition

Overpopulation can lead to competition. 1

Due to competition, some organisms (with useful traits) will live on… 2...but others will die. Also called “survival of the fittest”

The usefulness of a trait depends on the resources and environment. brighter stripes (+) attracting a mate? (-) more visible to predators? skinny body (+) hide or live in small holes? (-) not so strong for defense? Speedy swimmer (+) fast escapes (-) needs lots of energy (food!)

Organisms that have useful traits (adaptations) will survive and then reproduce. They pass the traits on to their offspring. 3

END RESULT: The environment now has a lot more organisms that have certain traits. This is NATURAL SELECTION. (Nature chooses the traits that will increase in the population. 4

HOMEWORK Page 31 – read and answer questions (Theory of Evolution)