Download Natural Selection

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