Download Natural Selection - Hicksville Public Schools

Aim: How does evolution occur by
natural selection?
How Does Evolution Occur?
• EVOLUTION is a slow change in a
species over time.
• Evolution occurs by a process
called NATURAL SELECTION.
Read this cartoon, what do you think NATURAL SELECTION is?
Darwin
•Considered the
“father” of evolution.
Charles Darwin traveled to the
Galapagos island, an uninhabited
environment, where he studied
evolution (Darwin’s Finches)
Darwin’s Theory of Evolution
Natural Selection:
• Individuals with favorable traits
are able to survive and
reproduce.
• Nature controls which traits are
favorable.
Natural Selection
• NATURAL SELECTION is the KEY to
Darwin’s theory.
•According to this theory, evolution is
controlled by NATURE.
•Only the organisms that are able to
SURVIVE and REPRODUCE will pass on
their genes.
Natural Selection vs.
Artificial Selection
People select the Environment selects
desirable traits that the desirable traits
will appear in the that will appear in
the
offspring.
offspring.
Mechanisms of Evolution:
• Overproduction
• Variation
• Natural Selection:
–Struggle For Survival
–Best Adapted To Survive
•Darwin did NOT have knowledge of
the genetic basis of inheritance
Overproduction
• More offspring are produced than can
survive.
• Overproduction leads to “Struggle for
Existence” or Competition.
– Compete for limited resources (food, water
and shelter).
– Only certain individuals are able to survive
and reproduce.
Overproduction
• More offspring are produced than can
survive (most die young).
Overproduction
leadsfish,
• Organisms
such as bacteria,
to have high reproinsects, and rabbits
ductive rates
because the chance that
COMPETITION!!
their young will survive is minimal.
Variation
• Variation: Individuals of the same
species have differences in their
appearance, structure, or genes.
• Increases the chance that some
members of a species will survive
an environmental change.
Sources of Variation
- Sexual Reproduction (sperm + egg)
+
=
- Meiosis (Independent Assortment.
& Crossing Over)
- Mutation (Change in DNA)
Mutations
• Mutations change the base
sequence of DNA
• Therefore Protein is changed
• Most mutations are HARMFUL, but
some can help the organism
SURVIVE.
Adaptive Value
• Adaptive Value: a change that produces a
trait that helps an organism survive.
– Ex: Camouflage
• If all the members of a species were the
same then an environmental change could
wipe out the entire species.
• VARIATION increases the chance that
some members of a species will survive.
Natural
Selection
Best
Adapted
To Survive
• The ENVIRONMENT ‘chooses’
which traits have adaptive value.
Organisms with
favorable traits in a
certain environment
will live to reproduce
and pass on those
traits, others will die
out.
Struggle For Survival
• “Survival of the fittest”
“Only those BEST suited will survive
because of competition for finite
(limited) resources (oxygen, water,
food, and shelter)
Conditions that lead to Evolution:
Using what you
have learned:
Summarize
evolution using
the words:
Overproduction,
Variation, Natural
Selection, adapt
to environment
Patterns Of Change
•
Species with SHORT reproductive cycles that
produce MANY offspring tend to evolve more
quickly than species with LONG life spans and
FEW offspring.
•
Types:
1) Gradualism – evolution occurs steadily
through time (Slow & Continuous) .
2) Punctuated Equilibrium- species stay the
same for long periods of time and then change
rapidly.
No Change
-------------
No Change
-----------
No Change
-------------
Extinction
• The disappearance of an entire species
(ex. Dinosaurs)
• It can be caused by temperature changes,
pollution, or landscape changes.