Unit 6 - Evolution

Evolution
 Simply said it means…

 “Descent with modification”
……. What does descent with modification mean?

change in the heritable characteristics of populations
over successive generations.
Two Opposing Views on
Evolution
DARWIN: LAMARK:
Believed traits
Father of Evolution were AQUIRED
Believed traits were “Use it or Lose it”

INHERITED
Darwin & Galapagos Islands
 Darwin’s Theory of Evolution was based on his studies in

the Galapagos Islands (off the northwest coast of South
America) during his voyage in the Beagle ship.
 He noticed that the animal and plant species in the
islands were similar but not the same.
Some Mechanisms of
Evolution
1. Natural Selection
2. Mutations
3. Artificial Selection
4. Sexual Selection
5. Genetic Drift
1. Bottleneck Effect
2. Founder Effect
Natural Selection:
Darwin observed that there were some
conditions for natural selection:
1. Population has variations of a trait.
2. Some variations are favorable.
3. More offspring are produced than survive.
4. Those that survive have favorable traits.
5. A population will change over time.
SURVIVAL OF THE FITTEST!!!

MICHAEL PHELPS ARNOLD SCHWARZENEGGER
Darwin’s Natural Selection:
 In summary:
 when populations with favorable variations (traits) in
the environment survive, reproduce, and pass these
variations on to the next generation, these populations
have evolved
Reminder:
•INDIVIDUAL ORGANISMS DO NOT EVOLVE!
•The smallest unit that can evolve is a
population, a collection of individuals of the
same species living in an area together
Mutations
 Changes in DNA sequence
 introduces variations of a gene in genepool of a
population
 variations can be beneficial
Or harmful.
Beneficial mutations allow
populations to survive,
reproduce, and evolve
Sexual Selection
 Mating that does not occur by chance
 Sexual selection: males compete for females
Artificial Selection
 “Man-made”
 Intentional breeding of individuals for a
desirable trait.
Genetic Drift
 change in the frequency of an existing trait in
a small population due to random events,
affecting survival and reproduction of
organisms.
Types:
Bottleneck Effect
Founders Effect
Bottleneck Effect
 sharp reduction in the size of a population
due to environmental events or human
activities
Founder Effect
 loss of genetic variation that occurs when a
new population is established by a very small
number of individuals from a larger
population
Adaptation
 Any trait/variation that aids in the chances of
survival and reproductive success of an
organism
 Darwin’s theory of natural selection can be

used to explain the evolution of various
adaptations in organisms
Structural adaptations
 Change in the structure of body parts
 May be used as a defense mechanism
 Mimicry – a structural adaptation that provides protection

for an organism by copying the appearance of another,
more dangerous species
 Camouflage – a structural adaptation that enables an

organism to blend in with its surroundings
Physiological adaptations
Ex. Antibiotic resistance, pesticide
resistance
 Changes in an organism’s metabolic or internal processes
Video 8 min
Types of Natural Selection
Stabilizing:
• Intermediate phenotype favored
• Population moves toward norm
Directional:
• Extreme phenotype is favored
• Population shifts in that direction
Disruptive:
• 2 or more extreme phenotypes favored
• Population splits
Types of Natural Selection
Evidence for Evolution
 Fossils
 Comparative Anatomy
 Biogeography
 Embryology
 Biochemical
 Fossils can show structural evolutionary changes over time
Horse Evolution
Evolution &
The Geologic Time Scale
 fossil records and dating techniques can

determine the approximate dates for events
on Earth
 Geologic Time Scale: represent different
times during which the Earth and its
organisms evolved
 Most fossils are found in

SEDIMENTARY rock.
 Comparative Anatomy: Anatomical structure
indicates evolutionary relationships
 Vestigial Structures: Functionless structures

indicate evolutionary pathways
 Ex.: wisdom teeth, appendix

Comparative Anatomy:
ANALOGOUS STRUCTURES:
- Same function, but no common descent.
-HOMOLOGOUS STRUCTURES:
 Different function, common descent.
 Genetic and embryological comparisons reveal hidden
relationships
Biogeography
 geographic distribution of organisms follows patterns
after the movement of tectonic plates over
geological time.
 Embryology: Embryological development
shows evolution from a common ancestor
Biochemical: Genetic (DNA) or protein comparisons
may reveal hidden relationships
Patterns of Macroevolution:
 Mass Extinction:
more than 99% of all species that ever lived are extinct
 Punctuated Equilibrium:
rapid evolution after long periods of equilibrium
 Gradualism: gradual transformation of a species
Patterns of Macroevolution
 Coevolution: 2 species evolve in response to changes in each other over

time
 Convergent Evolution
unrelated organisms come to resemble another
 Divergent Evolution or Adaptive Radiation
a species or group of species evolves into many
new species
Mechanisms of Speciation
 Species: A group of organisms that can interbreed and
produce fertile offspring
 New species are formed due to:
 Reproductive isolation rep isol video 2m
 Temporal isolation (Seasons/weather)
 Geographic isolation (far apart for a long time)
speciation video
Reproductive isolation:
Morphological differences in
damsel fly reproductive
organs
Damsel fly penises
Hardy-Weinberg Equilibrium
 A population that is not changing genetically is said to
be in Hardy–Weinberg equilibrium.
 assumptions that underlie the Hardy–Weinberg equilibrium:

 mating is random
 population is large
 no migration
 mutation can be ignored
 Natural selection is not acting on the population.
Hardy-Weinberg Equilibrium provides a baseline for scientists to
measure gene evolution in a given population.
two equations are necessary to solve a Hardy-Weinberg

question:
+ =1
²+2 + ²=1
 is the frequency of the dominant allele.
 is the frequency of the recessive allele.
 ² is the frequency of individuals with the homozygous dominant
genotype.
 2 is the frequency of individuals with the heterozygous genotype.
 ² is the frequency of individuals with the homozygous recessive
genotype.
Hardy-Weinberg Equilibrium
p2 + 2pq + q2 = 1
Homozygous Heterozygous Homozygous everyone

dominant recessive
- p = frequency of dominant allele

- q = frequency of recessive allele
- p2 = frequency of dominant genotype
- q2 = frequency of recessive genotype
Evolution Theory in a Nutshell
 DESCENT WITH MODIFICATION
 ECOLOGICAL COMPONENT: Life experiences by

individuals in a population can influence the flow of
genetic information from one generation to the next.
 GENETICS COMPONENT: If the genetic makeup of

a population is different in one generation from the
genetic makeup of the population in a previous
generation, this is an evolutionary result.

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Evolution

 Simply said it means…

……. What does descent with modification mean?

Believed traits were “Use it or Lose it”

 Darwin’s Theory of Evolution was based on his studies in

SURVIVAL OF THE FITTEST!!!

 Darwin’s theory of natural selection can be

 Mimicry – a structural adaptation that provides protection

 Camouflage – a structural adaptation that enables an

 fossil records and dating techniques can

 Most fossils are found in

 Vestigial Structures: Functionless structures

 Ex.: wisdom teeth, appendix

 Coevolution: 2 species evolve in response to changes in each other over

 assumptions that underlie the Hardy–Weinberg equilibrium:

two equations are necessary to solve a Hardy-Weinberg

Homozygous Heterozygous Homozygous everyone

- p = frequency of dominant allele

 DESCENT WITH MODIFICATION

 ECOLOGICAL COMPONENT: Life experiences by

 GENETICS COMPONENT: If the genetic makeup of

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