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)