Final Portion of
Evolution Notes:
• Darwin explained the
theory of evolution by
Natural Selection.
• Natural selection favors
adaptations within a
population.
Summary of Darwin’s Theory
1. Variation occurs naturally among members of
the same species.
2. More organisms are produced than can survive.
3. Competition exists between members of the same
species competing for limited resources.
4. Due to uniqueness, some have advantages while
others have disadvantages for their surroundings.
5. Individuals with the best traits for their environment
survive and produce the most offspring.
6. Species change over time. Due to natural
selection, there are characteristic changes in a
population in size and form. New species arise,
other species disappear.
7. Species alive today have descended with
modifications from species alive in the past.
8. All organisms on Earth are united into a single
tree of life by common descent.
Mass extinctions
• More than 99% of all species that ever
lived are now extinct
• Mass extinctions wiped out food webs
& ecosystems
• Example: Dinosaurs- asteroid could be
the cause but it could have been many
factors (such as volcanoes and
continents drifting)
Adaptive Radiation
• A species or group of species evolves into
many new species
Convergent Evolution
• Unrelated organisms come to resemble one another
bird
mammal
Coevolution
• 2 species evolve in response to changes in each
other over time
Central American Swollen-Thorn Acacias
Acacia ants and acacia trees
Acacias are small, Central American trees in the
Leguminosae. They have large, hollow thorns. The
acacia ants live in the thorns. On the tips of its
leaflets, the plant makes a substance used by the ants
as food. The ants defend the tree from herbivores by
attacking/stinging any animal that even accidentally
brushes up against the plant. The ants also prune off
seedlings of any other plants that sprout under
“their” tree
Punctuated Equilibrium
• Rapid evolution after long periods of equilibrium
(balance)
• Why? Migration, mass extinctions, isolation
Evidence for Evolution
The fossil record gave
us:
1. Descent with
modification
2. Homologous
Structures
3. Transitional
Fossils
Descent with Modification
• All living organisms are related to one another-
common descent
• Speciation- formation of a new species
Homologous Structures
• structures in different species that may
perform different functions but are similar
in structure because of their common
ancestry
• Examples: bat wing,
whale flipper, cat claw,
human hand
Vestigial Organs
– structures of no
apparent function to
an organism; leftover
from ancestry
– Examples: snakes
have leg and pelvis
bones; whale hae rear
limbs
Examples of Evolution
• Antibiotic Resistance: natural
selection has occurred within
populations of bacteria
• Mutations cause bacteria to change
their structure…antibiotics cannot
bind to cell surface
• Acquiring new genes…bacteria
have new enzymes that can
deactivate or destroy antibiotic
• Ex:Tuberculosis bacteria, lawyer
in Atlanta 2008
Examples of Evolution
• Darwin’s Finches: Natural selection has
occurred in beak size
Examples of Evolution
• Speciation: begins as a population adapts to its
environment.