Natural SelectionA 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

mateshelter

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 earlobe Attached 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.

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Due to competition, some organisms (with useful traits) will live on…

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...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.

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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.

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HOMEWORK

• Page 31 – read and answer questions

(Theory of Evolution)