Transcript Chapter 6 Notes - Tri-City

Zoology: Chapter 6
Pre-Darwinian Evolutionary Theories
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No set theory: based mainly in mythology and
superstition
Early Greeks
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Xenophanes, Empedocles, and Aristotle
Studied fossils and realized that they were evidence for
former life but failed to establish a real theory
Mid 1600’s – Archbishop Ussher established Earth’s
creation at 4004 B.C
Georges Buffon, mid 1700’s, established the idea of
changes in species and extended Earth’s age to
70,000years
Lamarckism: First Theory
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Jean Baptiste de Lamarck, late
1700’s, early 1800’s, came up
with the first written theory of
evolution.
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Proposed inheritance of
acquired characteristics
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Organisms, by striving to
meet the demands of their
environments, acquire
adaptations and pass them by
heredity to their offspring
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Giraffe’s neck length
Lamarckism cont.
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Lamarck’s theory was transformational
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Suggests individual organisms can change
characteristics to produce evolution
Transformational theories are now rejected
Darwin’s theory is variational
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Based off genetic variation in species
Evolutionary pressures have caused differential
survival and reproduction among species
Charles Lyell and Uniformitarianism
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Sir Charles Lyell
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British
Mid 1800’s
Geologist
Theory of uniformitarianism
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Laws of chemistry and physics remain the same
throughout history
Past geological events occurred by natural processes
similar to those observed today
Helped establish that Earth was millions of years old
Assignment
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Pg. 129
Questions 1 and 2
Read textbook pg. 103-106 for discussion
tomorrow.
Darwin’s Voyage
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Darwin sailed on the Beagle, a British ship
Journey began on Dec. 27, 1831 and lasted
roughly 5 years (1836)
Darwin was 23 years old when the trip began
The goal of the voyage was to survey South
America and the Pacific
This became one of the most important
voyages of the 19th century
Voyage continued
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During the voyage the Beagle stopped at
many ports and harbors along South America,
Australia, and the Pacific.
Darwin made collections of Fossils and made
observations about the flora and fauna of the
areas
He started to notice many similarities between
different areas and the species there
Arrives at the Galapagos Islands
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September 1835, the Beagle
arrived at the Galapagos Islands,
small island chain off the Pacific
Coast of South America (near
equator)
Darwin stayed 5 weeks on the
islands
He made observations of giant
tortoises, marine iguanas,
mockingbirds, and of course,
finches
All of these observations
changed his thinking and led to
the beginnings of his theory on
evolution.
How Darwin arrived at his theory
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Darwin compared the flora and fauna of the
Galapagos and the Cape Verde islands, which he too
visited.
He noted they were similar in climate and
topography, but vastly different in the plants and
animals that inhabited the islands
He came to conclusion life originated in South
America, spread, and adapted to each different
climate and environment
Darwin said the observations were “origin for all my
views”
The Voyage ends
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The Beagle returned to
England on October 2,
1836 and Darwin
conducted the rest of his
research there
3 years after the return, his
journal was published
He released On the Origin
of Species 20 years later
Side note: Darwin was a
weird dude; he also
married his cousin in 1839
Assignment
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Pg. 129
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Question 3
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Answer in a well written, grammatically
correct paragraph of 5-10 sentences
On the Origin of Species
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Darwin’s theory
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Perpetual Change
Common Descent
Multiplication of Species
Gradualism
Natural Selection
Perpetual Change
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The world is constantly in a state of change
Fossil record is evidence of this
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Change is both Earth’s environment over time, as
well as shifts in species across Earth’s history
Single celled to Fish to Reptiles to Mammals, etc
The Fossil Record
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Fossil record is biased because preservation is
selective
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Some animals do not leave behind many or any
fossils (jellyfish), where as vertebrates and things
with shells leave behind many fossils
Also some layers of fossils have been eroded or
broken apart by geologic processes
High heat also destroys fossils
Geologic time
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Relative dating has been used for ages, even
before Earth’s age was known
Now use radiometric dating (potassium-argon
40 ) typically to determine the ages of fossils.
Based on half-life of Potassium to degrade to
Argon
Can date fossils back millions of years. Back
to Precambrian time even
Evolutionary Trends
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Fossil record lets us study evolutionary
change across long periods of time
We have found
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Animal species typically survive 1-10 million
years, but this is highly variable
Across this time frame, the replacement of the
taxa and changes in species are observed
Horses are a great example:
Common Descent
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Darwin proposed all plants and animals arose
from a single ancestor
Phylogeny is the study of this “tree of life”
Pre-Darwin: multiple theories of origin
According to Darwin’s theory, one should be
able to trace their lineage back to a single
celled microbe that lived long ago
Homology and Phylogenetic
Reconstruction
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Homology: similar organs in different species
arose from a common organ and have just
been modified to fit the niche of the animal
Limbs of vertebrate are a prime example
Homology continued
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Darwin’s book The Descent of Man and
Selection in Relation to Sex used anatomical
comparisons of Man to Apes to suggest a
common ancestral lineage
Homologues are prime evidence for common
descent.
They form the basis for phylogeny and the
tree of life. They are so common in the living
world.
Ontogeny, Phylogeny, and
Recapitulation
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Ontogeny is the study of the development of
an organism throughout its life.
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Evidence for homology/common descent
Recapitulation/biogenetic law
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Ernst Haeckel: studied embryos and gave us this
statement: Ontogeny recapitulates phylogeny or
in simple words: Individual development repeats
evolutionary descent
Ontogeny continued
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Later von Baer, furthered the statement but
said that the homologies early in development
are more similar in species, however
development plays a big role in the final
“make up” of the creature.
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Animals with simple life cycles look closer to
their developmental stage than do those with long
complex life cycles
Multiplication of Species
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This is common sense with evolution.
Darwin believed that species separated by
some geographic features was the pressure
needed for new species to be produced
Interesting is that we can find where new
species divulge but the mechanism of how is
still very unknown.
What is a “species”
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Descent of all members from a common
ancestral population
Reproductive compatibility (they can
interbreed)
Maintenance within species with genotypic
and phenotypic cohesion ( lack of abrupt
differences between population in allele
frequencies and characteristics)
Now back to……..
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Speciation = species formation
Reproductive barriers prevent species from
interbreeding
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Arise gradually over long periods of time
Allopatric vs Sympatric Speciation
Allopatric Speciation
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Arises because of geographical separation of two
species that could interbreed
The 2 separated groups adapt and evolve and
reproduce at different rates, thus eventually forming
new species
Vicariant Speciation – geographical event
separates. Faulting, Mountains forming
Founder Event – few members leave a larger
population and settle elsewhere
Allopatric Speciation
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Vicariant speciation
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Consequences:
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Ancestral population is fragmented, however
fragments typically left intact.
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Does not directly induce evolution though. Other factors are
needed
Can divide several species simultaneously
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Effects numerous and diverse species most
Allopatric Speciation
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Founder event
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Migration of a small group to an area where no
members of their population are living
Fruit flies
Greatly reduces gene pool because of small
population size
Certain traits can be expressed or deleted
Nonallopatric Speciation
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Can a species ever arise without a geographical
barrier?
Speciation in lakes of Africa
Sympatric speciation
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Says that individuals within a species become specialized for
occupying different components of the environment
Or: By occupying different niches, members of a species acquire
enough adaptations to create reproductive barriers
Happens a lot in plants: Polyploidy in flowering plants
Adaptive Radiation
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A.R. – production of ecologically diverse
species from a common ancestral stock
Examples: volcanic islands, Galapagos Is.
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Essentially void of life at the beginning.
Darwin’s finches
Allows for many founder events because each
island is distinct in what plants inhabit it, etc
Gradualism
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Opposes arguments for sudden origin of species
Suggests that changes occur over numerous
generations and very slowly. No sudden changes
Populational gradualism vs. phenotypic gradualism
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Pop. Grad states that traits become established in a
population by increasing their frequency in the population
Phenotypic grad. States that new traits, even those
strikingly different from ancestral ones, are produced in a
series of small steps
Phenotypic Gradualism
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Highly controversial
Did not account for mutations
“sport” mutations were viewed as always
negative
Issues of “selective breeding” vs natural
causes controversy over phenotypic
gradualism still
Punctuated Equilibrium
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Alternative to phyletic gradualism: long term
constant change
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Not fully supported by fossil record
P.E. explains discontinuous evolutionary
changes observed throughout geological time
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Says that speciation events occur in a geological
instant
Allows plenty of time for Darwinian evolution to
occur still
Natural Selection
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Explains the origins of adaptations based
upon 5 observations
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Explains: all developmental, behavioral,
anatomical, and physiological attributes
Pg. 118-119 in text.
Oppositions to Natural Selection
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Natural selection has been challenged for
years
Orthogenesis – claims that directed
(nonrandom) variation governs evolution
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Variation has momentum that forces lineage to
evolve in a particular direction that is not always
adaptive
Irish Elk and antler size
Genetic research disproved this challenge
More challenges to Darwin
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Biggest issue: NS cannot generate new
structures or species; only modify previously
existing ones
Some early structures could not have
performed the function that their fully formed
structures do, thus unexplained how they are
favored
?? Some structures evolved for another
purpose then they are used for today
Neo-Darwinism
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Adds mechanism of inheritance
Population genetics and Darwin
made a major impact in the 1930’s in
modifying the theory
Microevolution
Macroevolution
Microevolution
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Study of genetic change occurring within
natural populations; observation of
polymorphism in the gene pool
Potential alleles can be enormous due to
mutations rates
Genetic Equilibrium
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Why haven’t recessive traits like blonde hair,
O blood type, etc disappeared totally
Hardy-Weinberg equilibrium states that
heredity alone does not produce evolution;
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In two parent populations, the allelic frequencies
and genotypic ratios attain an equilibrium in on
generation and remain constant thereafter,
unless……….disturbed?
How to Upset Genetic Equilibrium
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Random Genetic Drift
Nonrandom mating
Recurring mutations
Migration
Natural Selection
A combo of any of these
Genetic Drift
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Chance fluctuation in allelic frequencies from one
generation to the next; can result in the loss of alleles
from a population
Occurs in finite populations; small populations
Harmful to evolution because it restricts possible
genetic responses to environmental change
Ex: Cheetahs: very little genetic variation
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Stem from a very small population; can cause struggle to
survive
Nonrandom mating
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Selective breeding for certain traits
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Throws off Hardy – Weinberg equilibrium
Albinos with albinos (rare mutation)
Done in dogs often (tea cup species)
Inbreeding
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Increases homozygousity however increases
chances of rare genetic mutations to become
homozygous and expressed
Mutations
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Screw ups in the coding of your DNA
Can cause things from vitaligo to Tay-Sachs
to Down’s Syndrome, etc
Most mutations are missense (not expressed);
however some can be harmful
Migration
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If you divide a large population into smaller
populations, then genetic drift and selection
can cause evolutionary divergence of that
population; however, small amounts of
migrations keeps the species from becoming
too distinct genetically
Interactions of all these……
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Produces populations that are evolutionary
and qualitatively different then those
predicted by Hardy-Weinberg
Produce populations that are different then if
you remove the factors…..duh!!!
Hardy Weinberg equilibrium does not exist
for any significant period of evolutionary time
Macroevolution
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Major Evolutionary Change!!!!
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Gould suggested 3 tiers of times to observe
evolutionary processes.
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Tier 1: 10’s to thousands of years; the timescale of
population genetic processes
Tier 2: millions of years; covers time scale on which
rates of speciation and extinction can be measured
Tier 3: covers 10’s to 100’s of millions of years;
marked by periods of mass extinctions.
Speciation and Extinction through Geologic Time
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According to Darwin, each species has 1 of 2
fates: give rise to another species or become
extinct.
Rates of speciation and extinction vary, but
those with highest rates of speciation and
lowest rates of extinction produce the greatest
diversity of living things.
What traits lead to higher rates of speciation
and greater resistance to extinction??
Species Selection
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Cover a variety of traits and encompass
survival and multiplication of species among
different lineages.
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Mating rituals
Social structuring
Migration patterns
Geographic distribution
Descendent species will resemble their
ancestors in these species level traits
Species Selection
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Differential rates of speciation and extinction
can be caused by variation in organismal-level
properties
Ex: generalized vs. special feeding
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Specialized eaters would migrate more, and be
subjected to higher rates of geographic isolation
This means higher rates of speciation, however
also higher rates of extinction.
Mass Extinctions
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Mass Extinction – period where large
numbers of taxa go extinct simultaneously.
Occur at a rate of approx. 26 million years
5 Major Mass Extinctions
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Ordovician – 430 m.y.a.
Devonian – 350 m.y.a.
Permian – 225 m.y.a.
Trassiac – 200 m.y.a
Cretaceous – 65 m.y.a.
Mass Extinctions
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Permian
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225 million years ago
½ of shallow-water inverts disappeared
90% of marine inverts disappeared
Occurred in just a few million years
Cretaceous
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65 million years ago
Killed all dinosaurs, as well as some marine
inverts, and other small reptiles.
Assignment
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P. 129
Question 22
Compare and Contrast Microevolution and
Macroevolution
1 paragraph (grammatically correct, correct
punctuation, ect.)