Transcript naturally selected

EVOLUTION
UNIT
15-1 NOTES: ADAPTATIONS
AND NATURAL SELECTION
ADAPTATIONS
A hereditary characteristic that helps an organism survive
and reproduce in its environment.
FITNESS
Measure of ability to survive and produce more offspring relative
to other members of a population
ANIMAL
OBSERVATION
SO HOW DID THESE 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 the
environment is the selective
agent
• Mechanism by which evolution
occurs
Darwin said that in nature,
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
--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 organism to survive at 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 good traits down to their offspring
Natural Selection acts on phenotypes not genotypes
As environment changes, different traits will become beneficial.
EXAMPLES OF
NATURAL SELECTION
INSECTS BECOME
RESISTANT TO
INSECTICIDES.
Insecticide kills off most insects.
Those insects that survive have a gene that makes them resistant.
Resistant insects reproduce with other resistant insects.
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.
There were more dark moths
(on light trees) after 1850.