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Theories of Evolution
Jean Baptiste Lamarck
• similar species
descended from a common ancestor
• stated acquired traits were passed to
offspring (traits not determined by genes,
they are the result of an organism's
experience) – “Lamarckism”
– The environment made a structure useful or
useless, which in turn, caused the structure
to change
Theories of Evolution
Darwin & Wallace
• species were modified by natural
selection
– organisms best fit to survive in their
environment survive to reproduce
– “Survival of the Fittest”
• Fitness is how well an organism survives
and reproduces
Darwin
Wallace
Charles Darwin • Charles Darwin was the
naturalist on the HMS
Beagle. While on the ship,
he gathered the
observations that lead to the
theory of evolution through
natural selection. His ideas
were published in the book,
“On the Origin of Species by
Natural Selection.”
• Darwin stated: Over a long
time, nature determines
what traits/adaptations are
the most beneficial for a
species.
Darwin's Theories
• Descent with modification- newer
forms appearing in the fossil record are
actually the modified descendents of
older species
• Modification by natural selection-
Natural Selection vs. Artificial
Selection
– Natural: organisms with helpful traits
survive and reproduce to pass their
traits on. “Nature chooses”
– Artificial: organisms with specific
traits are selected and bred. “Man
chooses”
Adaptations Adaptations-
- Any heritable characteristic that
increases an organism’s ability to
survive and reproduce
- structural
- physiological
- behaviorial
Adaptations Structural Adaptation
Example: Camouflage
-Pepper Moths were once whitish with
black spots to blend with trees and
hide from predators. The Industrial
Revolution gave off so much pollution
that the trees turned black with soot.
A “mutated” blackish Pepper Moth that
would have been eaten on a white tree
survived to pass on its genes. Pepper
Moths are now blackish in color.
Adaptations Physiological Adaptations
– Venom in snakes
– Ink in sea hares
– Adaptations involving water
conservation in desert animals
Behavioral Adaptations
– Honey bee dances
– Mating rituals
Evidence of Evolution 1. Fossils- (there are holes in the record)
– Fossil- any trace of a long dead organism
usually found in sedimentary rock
– Fossil types
• mold- an imprint in rock in the shape of
an organism
• cast- a rocklike model of the organism
Law of Superposition- the oldest stratum is
the lowest and the youngest stratum is the
top layer
Biogeography- the study of the geographical
distribution of fossils & living organisms
Evidence of Evolution 2. Anatomy-
– homologous structures- looking for parts that are
similar in structure or function (from common
ancestry)
– analogous structures- parts that are alike in
function (NOT from common ancestry)
– vestigial structures- a structure that has no function
in today’s organism, but had a function in its
ancestors.
Evidence of Evolution 3. Embryology- comparison of embryos
Chicken
Fish
Turtle
Salamander
Pig Cow Rabbit Human
Evidence of
Evolution 4. Biochemistry-
comparison
of similarities
in DNA, RNA,
and
biochemical
functions
PATTERNS OF EVOLUTION 1. Divergent Evolution- species that were once
similar become increasingly
different
Adaptive Radiation- when an
ancestral species develops
an array of species
(Darwin’s Finches)
• This is a type of
divergent evolution
PATTERNS OF EVOLUTION 2. Convergent Evolution- species
that were once different
become increasingly similar
PATTERNS OF EVOLUTION
• Coevolution- the change of 2 or
more species in close association
with each other
Allele Frequencies Populations evolve, NOT INDIVIDUALS!
• Population- all members of a species
that live in an area.
• All alleles of a population are known as
the gene pool.
• The percentage of any specific allele is
the allelic frequency.
• If allelic frequencies do not change,
the population is in genetic
equilibrium.
Mechanisms That Change Genetic Equilibrium
1. Mutation
- chance (when DNA is copied)
- environmental factors (radiation, chemicals, etc.)
2. Genetic Drift
- chance events divide a population (volcanoes,
earthquakes, etc.) – this results in geographic isolation
- immigration & emigration resulting in gene flow
Mechanisms That Change Genetic Equilibrium
3. Small Population Size
- Bottleneck Effect – a change in allele
frequency following a dramatic reduction in the
size of a population
Mechanisms That Change Genetic Equilibrium
3. Small Population Size
- Founders Effect – allele frequencies change as
a result of the migration of a small subgroup of
a population
Mechanisms That Change Genetic Equilibrium
4. Non-random Mating
- sexual selection – organisms select mates for
size, color or another specific trait
Mechanisms That Change Genetic Equilibrium
5. Natural Selection
• There are 3 types of natural selection.
a. Stabilizing Selection- average individuals are favored
b. Directional Selection- one extreme variation of a trait is
favored
c. Disruptive Selection- individuals with extreme variations
of a trait are favored
Hardy Weinberg Principle
Hardy Weinberg Principle
Allele Frequencies in a population should remain
constant
p2 + 2pq + q
2 = 1 AND
frequency A + frequency a = 100
frequency AA + frequency Aa + frequency aa = 100
Speciation • Speciation- the evolution of a new
species
• Species- a population of organisms
that can successfully interbreed to
produce fertile offspring
Causes of Speciation
1. Geographic Isolation
2. Reproductive Isolation
- Temporal Isolation
3. Polyploidy
4. Behavioral Isolation