Transcript Ch 15 PPT

Evolution
Chapter 15
1
Evolution
“Nothing in
biology makes
sense EXCEPT
in the light of
evolution.”
Theodosius
Dobzhansky
Charles Darwin in later years2
15-1
Darwin’s Theory of
Natural Selection
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Early Ideas On Earth’s
Organisms
• Aristotle believed
species were fixed
creations arranged
by their complexity
• Idea lasted 2000
years
4
Contributor’s to Darwin’s thinking
included:
:
• Charles Lyell –geologic processes still
changing Earth – (Principles of
Geology book)
• Georges Cuvier – species extinction
(Catastrophism)
• Thomas Malthus – struggle for
existence (resources)
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Contributor’s to Darwin’s thinking
included:
:
• James Hutton - Gradualism
• John Baptiste Lamarck – developed
idea of change over time. Inheritance
of Acquired Characteristics and Law
of Use and Disuse
• Alfred Russel Wallace – organisms
evolved from common ancestors
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Lamarck’s Theory of
Evolution
• Law of Use and
Disuse
• If a body part were
used, it got
stronger
• If body part was
NOT used, it
dissappeared
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8
Lamarck’s Theory of
Evolution
• Inheritance Of Acquired Traits
– Traits Acquired During Ones Lifetime
Would Be Passed To Offspring
Clipped ears of dogs could be passed to offspring!
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Lamarck’s Mistakes
• Lamarck Did NOT Know how
traits were inherited (Traits are
passed through genes)
• Genes Are NOT Changed By
Activities In Life
• Change Through Mutation
Occurs Before An Organism Is
Born
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Charles Darwin the
Naturalist
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Voyage of the Beagle
Charles Darwin
• Born Feb. 12, 1809
• Joined Crew of HMS
Beagle, 1831
• Naturalist
• 5 Year Voyage around
world
• Avid Collector of Flora
& Fauna
• Astounded By Variety
of Life
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Darwin’s Voyage of Discovery
A reconstruction of the HMS Beagle sailing off Patagonia.
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Darwin Left England in 1831
Darwin returned 5 years later in 1836
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The Galapagos Islands
• Small Group of Islands 1000 km West
of South America
• Similar Climates
• Animals On Islands Unique
• Tortoises
• Iguanas
• Finches
• Mockingbirds
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The Galapagos Islands
• Volcanic islands off
the coast of South
America
• Island species varied
from mainland
species & from
island-to-island
species
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The Galapagos Islands
• Finches on the islands resembled a
mainland finch
• More types of finches appeared on the
islands where the available food was
different (seeds, nuts, berries, insects…)
• Finches had different types of beaks
adapted to their type of food gathering
• Mockingbirds had different traits suited
for their niche!
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Darwin’s Observations
• Patterns of
Diversity were
shown
• Unique
Adaptations in
organisms
• Species Not Evenly
Distributed
• Australia,
Kangaroos, but No
Rabbits
• S. America, Llamas
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Darwin’s Observations
• Both Living
Organisms &
Fossils collected
• Fossils included:
•Trilobites
•Giant Ground
Sloth of South
America
This species NO longer existed.
What had happened to them?
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Definition
• Evolution is
the slow,
gradual
change in a
population of
organisms over
time
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Darwin’s Observations
• Left unchecked, the number of
organisms of each species will
increase exponentially,
generation to generation
• In nature, populations tend to
remain stable in size
• Environmental resources are
limited
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Darwin’s Conclusion
• Production of more
individuals than can be
supported by the
environment leads to a
struggle for existence
among individuals
• Only a fraction of
offspring survive each
generation
• Survival of the Fittest
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Darwin’s Observations
• Individuals of a
population vary
extensively in their
characteristics with no
two individuals being
exactly alike.
• Much of this variation
between individuals is
inheritable.
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Darwin’s Conclusion
• Individuals who
inherit
characteristics most
fit for their
environment are
likely to leave more
offspring than less fit
individuals
• Called Natural
Selection
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Darwin’s
Theory
of
Evolution
•The unequal ability of individuals to
survive and reproduce leads to a gradual
change in a population, with favorable
characteristics accumulating over
generations (natural selection)
•New species evolve
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Natural Variation and Artificial
Selection
• Abandoned The Idea That Species Were
Perfect & Unchanging
• Observed Significant Variation in All
Species Observed
• Observed Farmers Use Variation To
Improve Crops & Livestock
• Called Selective Breeding
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Natural Variation and Artificial
Selection
• Natural Variation
– Differences Among Individuals Of A
Species
• Artificial Selection
– Selective Breeding To Enhance
Desired Traits Among Stock or Crops
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Natural Selection
• 4 Principles of
Natural Selection:
• 1. Variation
• 2. Heritability
• 3. Overproduction
• 4. Reproductive
Advantage
.
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Natural Selection Concepts
• The Struggle for Existence (compete for
food, mates, space, water, etc.)
• Survival of the Fittest (able to survive and
reproduce)
• Descent with Modification (new species
arise from common ancestor replacing
less fit species)
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Survival of the Fittest
• Fitness
– Ability of an Individual To
Survive & Reproduce
• Adaptations Can Be:
– Physical
• Speed, Camouflage, Claws,
Quills, etc.
– Behavioral
• Solitary, Herds, Packs,
Activity, etc.
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Natural Selection
• Cannot Be Seen Directly
• It Can Only Be Observed As
Changes In A Population Over
Many Successive Generations
– Radiation
– Fossil Record
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Evidence for Evolution – Evolution Observed
Selection against small guppies results in an increase in
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average size
Descent With Modification
• Takes Place Over Long Periods of
Time
• Natural Selection Can Be
Observed As Changes In
– Body Structures
– Ecological Niches
– Habitats
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Descent With Modification
• Species Today Look Different
From Their Ancestors
• Each Living Species Has
– Descended
– With Changes
– From Other Species
– Over Time
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Descent With Modification
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Descent With Modification
• Implies
– All Living Organisms Are Related
– Single Tree of Life
• DNA, Body Structures, Energy
Sources
• Common Descent
– All Species, Living & Extinct, Were
Derived From Common Ancestors
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Theory of Evolution
Today
Supporting Evidence
15-2
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Evidence of Evolution
Key Concept
Evidence For This Process Could Be Found
In:
– The Fossil Record
– The Geographical Distribution of Living
Species
– Homologous Structures of Living
Organisms
– Similarities In Early Development
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Fossil Record
• Earth is Billions of Years Old
• Fossils In Different Layers of Rock
(sedimentary Rock Strata) Showed
Evidence Of Gradual Change Over
Time
• Derived Traits – newly evolved
features
• Ancestral Traits – old features
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Evidence for Evolution – The Fossil Record
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Geographic Distribution of
Living Species
• Different Animals On
Different Continents
But Similar
Adaptations To
Shared Environments
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Homologous Body Structures
• Scientists Noticed Animals With
Backbones (Vertebrates) Had Similar
Bone Structure
• May Differ In Form or Function
• Limb Bones Develop In Similar
Patterns
• Arms, Wings, Legs, Flippers
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Homologous Body Structures
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Homologous Structures
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Vestigial Body Structures
• Not All Serve Important Functions
– Vestigial Organs
• Appendix In Man
• Legs On Skinks or Leg Bones on Snakes
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Analogous Structures
• Used the same but was not made the same
way.
• Bird wings versus insect wings
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Similarities In Early
Development
• Embryonic Structures Of Different
Species Show Significant Similarities
• Embryo – early stages of vertebrate
development
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Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
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Chicken
Turtle
Rat
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Human Fetus – 5 weeks
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Similarities in DNA Sequence
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Adaptations
• Camouflage
• Mimicry
• Antimicrobial Resistance
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Evolutionary
Time Scales
Macroevolution:
Long time scale
events that
create and
destroy species.
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Evolutionary
Time Scales
Microevolution:
Short time scale
events (generationto-generation) that
change the
genotypes and
phenotypes of
populations
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Shaping Evolutionary Theory
15-3
• Population Genetics
– Hardy-Weinberg Principle – genetic
equilibrium (constant frequencies over time)
– p + q = 1 – allele frequency
– p2 + 2pq + q2 = 1 – genotypic frequency
– Table 15.3 (page 432)
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Mechanisms of Evolution
•
•
•
•
•
•
•
Genetic Drift
Founder Effect
Bottleneck
Gene Flow
Nonrandom Mating
Mutation
Natural Selection
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Genetic Drift
• In each generation, some individuals may, just by chance, leave
behind a few more descendents (and genes, of course!) than other
individuals. The genes of the next generation will be the genes of
the “lucky” individuals, not necessarily the healthier or “better”
individuals. That, in a nutshell, is genetic drift. It happens to ALL
populations—there’s no avoiding the vagaries of chance.
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Founder Effect
• A founder effect occurs when a new colony is started by a few members of
the original population. This small population size means that the colony
may have:
– reduced genetic variation from the original population.
– a non-random sample of the genes in the original population.
– Example, the Afrikaner population of Dutch settlers in South Africa is
descended mainly from a few colonists. Today, the Afrikaner
population has an unusually high frequency of the gene that causes
Huntington’s disease, because those original Dutch colonists just
happened to carry that gene with unusually high frequency. This effect
is easy to recognize in genetic diseases, but of course, the frequencies
of all sorts of genes are affected by founder events.
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The elephant seal
population was
• Population bottlenecks occur when a
bottlenecked due to
population’s size is reduced for at least
hunting in the 1890s.
one generation. Because genetic drift
Bottleneck
acts more quickly to reduce genetic
variation in small populations,
undergoing a bottleneck can reduce a
population’s genetic variation by a lot,
even if the bottleneck doesn’t last for
very many generations. This is
illustrated by the bags of marbles
shown above, where, in generation 2,
an unusually small draw creates a
bottleneck.
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Gene Flow
• Some individuals from
a population of brown
beetles might have
joined a population of
green beetles. That
would make the genes
for brown beetles
more frequent in the
green beetle
population.
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Nonrandom Mating
• Sexual Selection – individuals choose mates
based on certain traits.
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Mutation
• A mutation could cause parents with
genes for bright green coloration to have
offspring with a gene for brown
coloration. That would make the genes for
brown beetles more frequent in the
population.
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Natural Selection
• There is variation in traits.
• There is differential reproduction.
• There is heredity.
• One trait tends to become more common.
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Types of Selection
• 3 types of Natural Selection:
– Stabilizing - average
– Directional – one extreme
– Disruptive – both extremes
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Reproductive Isolation
• Prezygotic
–
–
–
–
–
Habitat isolation
Temporal isolation
Behavioral isolation
Mechanical isolation
Gametes die
• Postzygotic
–
–
–
–
Zygote dies
Hybrids sterile
Hybrids inviability
Low hybrid fitness
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Speciation
• Allopatric – due to
geographic isolation.
Isolation might occur
because of great distance or
a physical barrier, such as a
desert or river
• Sympatric - Merely
exploiting a new niche may
automatically reduce gene
flow with individuals
exploiting the other niche.
This may occasionally
happen when, for example,
herbivorous insects try out a
new host plant.
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Patterns of Evolution
• Divergent Evolution
– Adaptive radiation
• Coevolution
– Predator/prey and
parasite/host
– Competitive species
– Mutualistic species
• Convergent Evolution
– Analogous features
– Bird and bat wings
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