Evolution Notes
Biology 102A
Fall 2008
• Darwin explained the
theory of evolution by
Natural Selection.
• “Survival of the Fittest”
means organisms that
adapt to their
environment survive,
while organisms that do
not adapt disappear.
• Natural selection leads
to adaptations within a
population.
Types of Evolution
• Microevolution- the change of allele frequencies
within a population
• Macroevolution- large-scale evolutionary changes
: 5 patterns
l. Mass extinctions
2. Adaptive Radiation
3. Convergent Evolution
4. Coevolution
5. Punctuated Equilibrium
Mass extinctions
• More than 99% of all species that ever
lived are now extinct
• Mass extinctions wiped out food webs
& ecosystems
• Example: Dinosaurs- asteroid but
could have been many factors
(volcanoes & 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
fish
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-new species can arise
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 & pelvis
bones; whale 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
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.