Download 8-5 Notes: Natural Selection

8-5 Notes:
Natural Selection
SO HOW DID ORGANISMS BECOME
SO WELL ADAPTED TO THEIR
ENVIRONMENT?
DARWIN’S EXPLANATION
Darwin proposed that animals
evolved to fit their
environments.
EVOLUTION
The change in a population of organisms over
time
DARWIN’S EXPLANATION
• Darwin realized that animals have many
offspring and some don’t survive.
• The survivors are better suited to their
environment.
HE CALLED THIS
PROCESS….
NATURAL SELECTION
• Mechanism by which
EVOLUTION occurs
• The environment is
the selective agent
Darwin said that in nature,
the environment creates
selective pressure
STEPS OF NATURAL SELECTION
1. Overproduction
-organisms have many offspring, but not
all will survive.
STEPS OF NATURAL SELECTION
2. Genetic Variation
• Individuals vary within a
population
STEPS OF NATURAL SELECTION
2. Genetic Variation
• Individuals vary within a
population
• New traits appear due to
genetic mutations
STEPS OF NATURAL SELECTION
3. Struggle to Survive
• Organisms compete for resources (food, water,
shelter, and mates)
• Organisms have to get away from predators
STEPS OF NATURAL SELECTION
3. Struggle to Survive
• Some adaptations allow organisms to survive
at a higher rate and individuals are “naturally
selected” to survive and produce offspring
STEPS OF NATURAL SELECTION
4. Descent with Modification
•
Organisms with the best adaptations will
survive and reproduce passing these beneficial
traits down to their offspring
NATURAL SELECTION
• Natural Selection acts on PHENOTYPES
(traits) not genotypes
NATURAL SELECTION
• Natural Selection acts on PHENOTYPES
(traits) not genotypes
• As environment changes, different traits will
become beneficial.
EXAMPLES OF
NATURAL SELECTION
INSECTS BECOME
RESISTANT TO
INSECTICIDES.
1. Insecticide kills off most insects.
2. Those insects that survive have a gene that
makes them resistant.
3. Resistant insects reproduce with other
resistant insects.
4. Their offspring have the resistant gene.
Insecticides don’t work very well over time!
OTHER EXAMPLES OF
EVOLUTION:
• Bacteria become
resistant to antibiotics
• Don’t take antibiotics
unless you have a
bacteria infection!
OTHER EXAMPLES OF
NATURAL SELECTION:
• Peppered Moths in England
• There were more light moths (on
light trees) before 1850.
OTHER EXAMPLES OF
NATURAL SELECTION:
• Peppered Moths in England
• There were more dark moths (on dark trees) after
1850.
ARTIFICIAL
SELECTION
Humans breed for specific traits causing
differences in species (i.e. dog breeding)