Transcript Natural Selection

Natural Selection
and Evolution!
Why two types of
clover?
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What advantages does the striped clover have? The
plain?
How does cyanide help/hurt these plants in different
habitats?
Organisms have
variation
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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
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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
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Humans and nature “choose” which organisms win and get
to procreate
Artificial selection = human select most useful variations,
allow those to reproduce
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ex: race horses - what trait would
be selected for?
ex: broccoli and other veggie
friends
The struggle for
existence
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Resources are limited, so only some can
survive
Natural Selection = individuals better adapted
to their environment survive, reproduce, and
pass on their genes
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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
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Descent with modification = over time,
natural selection produces organisms with
differences from their ancestors
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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)