Download Chapter 7-Evolution

Chapter 7
Evolution and the Fossil Record
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Chapter 7 - Guiding Questions
• What lines of evidence convinced Charles Darwin that organic
evolution produced the species of the modern world?
• What are the components of natural selection?
• What is the source of the variability that is the basis of natural
selection?
• What role does geography play in speciation?
• What factors lead to evolutionary radiation?
• Why is convergence one of the most convincing kinds of evidence that
evolutionary changes are adaptive?
• Why do species become extinct?
• What is mass extinction?
• In what ways can evolutionary trends develop?
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Evolution
Evolution
– changes in populations,
which consist of groups
of individuals that live
together and belong to the
same species
– a change in gene
frequencies
– populations evolve, not
individuals
• YOU can’t evolve!
Extinct ground sloth (20 ft long)
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Evolution
Adaptations
– specialized features of
animals and plants (or any
other organism) which
perform one or more useful
functions
– allow that organism to excel
in its environment
– YOU can only modify
characteristics over which
your genes have control; e.g.,
tanning
Cat skull
Horse skull
Venus Flytrap
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Inefficient Evolution
• can only operate by changing what is
already present;
• it’s the business of remodeling rather than
new construction from scratch
• e.g., to make a new structure, natural
selection starts by modifying an already
existing one
– e.g., how could ‘night vision’ evolve?
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Charles Darwin
• 1831
– set sail on the Beagle
– schooled in
uniformitarianism
• Lyell’s Principles of
Geology
– a keen observer of
natural phenomena
• 1859-On the Origin of
Species by Natural
Selection
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Some of Darwin’s Observations
• Rhea
– large flightless birds
– found only in South
America
– also found extinct,
fossil forms
• Some similarities but also
obvious differences from
ostrich (Africa) and emu
(Australia)
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More of Darwin’s Observations
• sloths and extinct
armadillos
– unique to the Americas
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More of Darwin’s Observations
• Oceanic islands
– many barren; Hawaii
has no native snakes,
frogs, FW fish, etc.
– species must have
originated elsewhere
• Galápagos Islands
– tortoises with shells
unique on each island
– shared a common
ancestry
– followed later by
differentiation
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Galapagos Islands
Range from 3 to 5 my old
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Galapagos Tortoises
• 14 subspecies, 11 extant, several with very
small populations
– e.g., Lonesome George
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Lonesome George
Isla Pinta
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Darwin’s Famous Finches
• Finches of the Galápagos
– different beak types
• slender-insectivorous
• sturdy-seed crushing
• woodpecker-like-tool user
– differentiation based on lifestyle
– curiously resemble a South American
mainland finch
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Adaptive Radiation of Darwin’s Finches
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Feeding Adaptations of Ground Finches
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Charles Darwin
• Additional observations
– Anatomical relationships
• embryos of many vertebrates are quite similar, even
superficially indistinguishable
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Charles Darwin
• Additional observations
– Anatomical relationships
• embryos of many vertebrates quite similar
• homology
– presence in two different groups of animals or plants of
organs that have the same ancestral origin but serve
different functions
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Charles Darwin
• Additional observations
– Anatomical relationships
• embryos of many vertebrates quite similar
• homology
– presence in two different groups of animals or plants of
organs that have the same ancestral origin but serve
different functions
• vestigial organs
– organs that serve no apparent purpose but resemble organs
that perform functions in other creatures
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Pelvic structures in whales and snakes
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Vestigial Structures
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Theory of Evolution
• Natural Selection- ‘survival of the fittest’
– the process that operates in nature but parallels
the artificial selection by which breeders
develop new varieties of plants and animals
• success of an individual determined by advantages it
has over others
– survives to bear offspring with same trait
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Antibiotic Resistant Bacteria
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The Basis for Natural Selection
• There is much variation between members
of a species.
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The Basis for Natural Selection
1. There is much variation between members
of a species
2. Reproduction is way in excess of the
number that the habitat can survive
e.g., Robins
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E.g., Robins
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The Basis for Natural Selection
1. There is much variation between members
of a species
2. Reproduction is way in excess of the
number that the habitat can survive
e.g., Robins
3. Differential reproductive success-those
best adapted survive to reproduce the most
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Will the all survive?
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Theory of Evolution
• Darwin didn’t have all the tools we have today to
explain his idea.
• Genetics was in its infancy—Mendel’s ideas, though
contemporary with Darin, weren’t appreciated for
decades.
• Genes-hereditary factors
• Particulate inheritance
– Gregor Mendel’s idea that organisms retain identities through
generations
– Peas
• No blending
• Colors could be masked for generations
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Theory of Evolution
• Mutations
– alteration of genes
– provides for variability
– very few are helpful
• DNA
– Deoxyribonucleic Acid
– transmits chemically
coded information
– mostly found in
chromosomes
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Theory of Evolution
• sexual recombination
– each parent contributes one half of its chromosomes to offspring
via a gamete
• special reproductive cell containing one of each type of chromosome
– female ovum/egg; male sperm
– yields new combinations-e.g., my kids aren’t exact copies of me;
genes of their mother and me are both present.
• mutations increase variability—and we all have them!
• gene pool
– sum total of genetic components of a population or group of
interbreeding individuals
– you have only a small subset of the human gene pool
• reproductive barriers limit the pool and keep species separate
• speciation
– origin of a new species from two or more individuals of a
preexisting species
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Reproductive Isolation
Spring breeder
Fall breeder
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Origination
• Evolutionary radiations
– pattern of expansion from some ancestral adaptive
condition represented by descendant taxa
• adaptive breakthrough
– appearance of key features that allow radiation to occur
• fossil record documents patterns
– E.g., Jurassic corals
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Jurassic Corals
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Origination
• Rates of speciation
– Galápagos Islands-formed millions of years ago
– Lake Victoria
• 13,000 years old
• 497 unique species of cichlid fish, many with specialized
adaptations
• Molecular clock
– assume average rate of mutation
– determine pace of change
– extrapolate timing of change
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Convergence
• Evolution of similar
forms in two or more
different biological
groups
• Marsupials and
placental mammals
– similar form
– isolated, adaptive
convergent evolution
after initial divergence
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• caused by extreme
impacts of limiting
factors
Extinction
– predation
– disease
– competition
• pseudoextinction
– species evolutionary
line of descent
continues but
members are given a
new name
• high rates of
extinction make
useful index fossil
– ammonoids
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Extinction
• rates
– average rate has
declined through
time
• mass extinctions
– many extinctions
within a brief
interval of time
– largest events peak
at extinction of
>40% genera
– rapid increase
(radiation) follows
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Modern Mass Extinctions
• fossil patterns
reflected in modern
– tropical species
– large animals
• loss of habitat
• direct exploitation
• likely replacement by
opportunistic species
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Evolutionary Trends
• Cope’s rule
– body size increases
during evolution of a
group of animals
– structural limitations
on size
• specialized adaptations
limit evolution
– elephants
– manatees
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Evolutionary Trends
Whales
• terrestrial origin
– 50 Ma
– small (2 m)
mammals with
feet
• marine adaptation
–
–
–
–
40 Ma
lost hind limbs
no pelvic bones
up to 20 m
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Phylogeny
• Phylogeny
– complex, large-scale
trend within a
branching tree of life
– gradual large-scale
change from one
species to another is
rare
• e.g., Jurassic coiled
oysters
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Phylogeny
• Axolotl
– example of rapid speciation
from parent species
• parent is amphibious
• offspring is aquatic
throughout life after one
simple genetic change
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Phylogeny
• rates
• gradualistic model
– very slow rates
• punctuational model
– rapid evolution with
little change between
steps
– bowfin fish
• little change in 60 m.y.
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Phylogeny
• Horses
– increase in body size
– evolved tall complex molars
and single-hoofed toe
– change driven by climate
• expansion of grasslands
• Dollo’s law
– evolutionary transition from
at least several genetic
changes is highly unlikely
to be reversed by
subsequent evolution
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