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EVOLUTION!
Summing it all up!
What is Scientific Theory?
•In science, theories are
statements or models that
have been tested and
confirmed many times.
In science, the term "Theory" does not
express doubt.
•They explain a wide variety of data
and observations
They can be used to make
predictions
They are not absolute, can be
changed as new evidence is found
•
•
The theory of evolution is considered a
UNIFYING THEORY of Biology, because it
answers many questions and offers an
explanation for observations
History of Evolution
•Charles Darwin
developed the
THEORY OF
EVOLUTION BY
NATURAL SELECTION
•explained how
organisms changed
over time (ADAPTED)
Acquired Characteristics
•Lamarke's Theory of
Acquired
Characteristics
Some thought that
you would gain or lose
features if you
overused or didn't use
them,
PROVEN TO BE
WRONG!
•
•
Macroevolution:
Evolution of a
New Species
Levels of Evolutionary Study
• Microevolution: examines changes to the genes
(alleles) within populations
– Population Genetics: studies the changes in the
numbers & types of alleles in a population
• Examines evolution within a species.
• Small changes that do not lead to new species, but can
lead to new variations.
• Macroevolution: examines the evolutionary
changes that create new species
– Speciation: the formation of new species over time
Macroevolution
• Species: a group of organisms that can
interbreed and produce fertile offspring
• Speciation: the evolution of new speices
(by genetic change or change in form)
–Occurs when members of a similar
populations can no longer interbreed!
Methods of Speciation
• Geographic Isolation: physical barriers divide
a population and prevent interbreeding
Beetles in Grassland
Become Green
Beetles in Woody Habitat
Become Brown
Methods of Speciation
• Reproductive Isolation--occurs when formerly interbreeding
organisms can no longer mate & produce fertile offspring
– Genetic: genetic differences are too great to breed
successfully
– Behavioral: mating behaviors or mating seasons don’t
allow for mating
• Chromosome Numbers
– Polyploidy: any species with extra sets of chromosomes.
Common in plants.
• Can interbreed or self-fertilize, forming separate
species
– Hybridization: when two closely related species attempt to
mate
• Usually results in sterile offspring
• Ex: donkey + horse = mule
Speed of Speciation
• Gradualism
– Idea that species originate thru a slow, gradual
change of adaptations over long periods of time
• Punctuated Equilibrium
– Idea that species can remain stable for long
periods of time until environmental changes
cause many new species to appear
• Speciation occurs in less than 10,000 years!
Patterns of Macroevolution:
Divergent Evolution
• Species diverge or
become increasingly
distinct from one
ancestral species
• Ex: Darwin’s finches
• Also called adaptive
radiation
Patterns of Macroevolution:
Convergent Evolution
• Process by which unrelated species become
similar as they adapt to similar environments
Ostrich
Emu
Australia
Africa
Rhea
South
America
Patterns of Macroevolution:
Coevolution
• When species who live in close contact
evolve adaptations to one another’s
existence.
Extinction!
• When all the members of a species die off or
fail to reproduce
– Estimated that 99% of all species that ever lived
have become extinct
– Most extinctions are the
result of environmental
change, can cause well
adapted species to become
poorly adapted!
– If the environment changes
faster than a species can adapt,
extinction can result!
Microevolution
Processes of Microevolution
• Microevolution examines the processes
by which inherited traits change over
time in a population
–Natural Selection
–Migration
–Mate Choice
–Mutation
–Genetic Drift
Processes of Microevolution
• Natural Selection: changes in environmental
pressures can cause an increase or decrease in
certain alleles (traits) in a population
– Favorable alleles stay in population (selected for)
– Unfavorable alleles are eliminated (selected against)
• Migration: as organisms move from one population
to another, their genes move with them
– Causes the numbers and types of alleles within each
population to change.
Processes of Microevolution
• Mate Choice: if parents are selective (picky) or
limited in their choice of mates, only a limited set of
traits will be passed on
• Mutation: can add a new allele to a population
– Mutations are rare, and must occur in egg or sperm to be
passed on
• Genetic Drift: population sizes affect the change in
alleles (traits) in a population
– Large populations experience slower changes in alleles
– Smaller populations can change more quickly
Microevolution:
Changes within Populations
 Populations evolve NOT individuals evolve
Natural selection works on the phenotypes within a
population
Individuals cannot evolve within their lifetime,
because they cannot evolve a new phenotype due to a
change in the environment
Evolution is brought about by breeding that occurs
between organisms within a population. Natural
selection maintains favorable (useful) genotypes, and
eliminates unfavorable (not useful) genotypes.
Natural Selection
- Explains how organisms change over time
1. Over Production: Most organisms produce more
offspring than will survive
2. Variation: Members of the population have
variations
3. Selection: Certain variations will increase the
likelihood of survival
4. Adaptation: Over-time organisms with that
variation make up most of the population and
may look different than their ancestors
Patterns of Natural Selection
Stabilizing
selection:
Directional
selection:
Favors average
individuals; reduces
variation
Favors EXTREME
variations;
evolution is fast
Disruptive selection:
Favors two
extreme variations;
no intermediate
and eventually two
species.
Stabilizing Selection
• “Average” individuals are better able to survive
• Alleles for the “extreme” are eliminated
• A narrow range of
phenotypes is favored
resulting in a narrow
bell shaped curve
Directional Selection
• ONE extreme is favorable, but other is not
• Alleles for other extreme and normal phenotypes
become less common in the population
• Results in FAST
evolution!
• Bell curve is shifted
off of center
Disruptive Selection
• BOTH extremes are favorable!
• Results in increasingly distinct phenotypes,
the “normal” phenotype is selected against
• Bell curve is
‘disrupted’ and
pushed apart
into two peaks
Evidence for Evolution
Evidence for Evolution
• Fossils
– provide a record of
early life &
evolutionary history
– Currently, the fossil
record is incomplete
(like a jigsaw puzzle w/
missing pieces)
– The more fossils
discovered, the clearer
the evolutionary
picture becomes!
Evidence for Evolution
• Biogeography
–The study of the locations of organisms
around the world
–Organisms in similar
environments have
similar adaptations
despite being on
completely different
continents.
•Ex: Large, flightless birds
Evidence for Evolution
• Anatomy
–the way an organism is put together
–Homologous structures
–Analogous Structures
–Vestigial Structures
Homologous Structures
• Parts with a common evolutionary history
– Ex: Organisms that have the same basic skeleton, bones
are just modified for different functions
– It would be unlikely
for so many animals
to have similar
structures if each
species arose
individually!
Analogous Structures
• Body parts that are similar in function, but
not evolutionary origin
• Ex: Wings of a butterfly & wings of a bird
Vestigial Structures
• Body structure that has no function in
present day organisms, but was probably
useful to an ancestor
• Ex: Eyes on Naked Mole Rats, Appendix in
humans, Wings on ostrich
Evidence for Evolution
• Adaptations: Structural
– Develop over many
generations (ex: claw length,
fur color, etc)
•Mimicry: enables one
species to resemble
another species.
Monarchs and Viceroys
•Camouflage: enables
species to blend in with
their surroundings
Monarch
TOXIC!
Viceroy
TASTY!
Evidence for Evolution
• Adaptations: Physiological
– Changes in an organisms
metabolic processes (occurs
more rapidly)
• Bacteria’s resistance to
antibiotics
• Insects / weeds
resistance to
certain
pesticides
Evidence for Evolution
• Embryological
– similarities between young embryos suggest
evolution from a distant common ancestor
Evidence for Evolution
• Biochemical
– Provides info about
relationships between
individuals and species
– Uses RNA & DNA
sequences to construct
cladograms
(evolutionary
diagrams)