Transcript Evolution

Lamarck’s evidence and inference

Comparisons between
current species and
fossils: lines of
descendents
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Use and disuse
Inheritance of
acquired
characteristics
Darwin’s evidence and inferences
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1. All species produce far more
offspring than required just to
replace parents. This would result
in exponential growth if
populations were not limited.
("Essays on Population" by Thomas
Malthus)
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2. Populations do not, however,
increase exponentially. They
generally remain stable in size.
(Field observations at home and
on the voyage of the Beagle)
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3. The resources in the
environment are limited.
observations)
(Field
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1. Because of the limited
resources in the
environment, there is
competition among
individuals. Only a small
fraction of the individuals
born can survive.
Darwin’s evidence and inferences
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4. There is variation within
species and populations.
Some individuals possess
characteristics that are better
suited to the environment
than others. (Field
observations)
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5. Most physical, and some
behavioral characteristics are
inherited.
(Breeding experiments with
pigeons. "Artificial selection")
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2. Those individuals with the best
characteristics for the particular
environment will do a better job
of producing and providing for
offspring than will others with less
"fit" characteristics.
Darwin’s evidence and inferences
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6. Geologic
processes are very,
very slow.
(Principles of
Geology by Charles
Lyell, work by
Hutton, as well as
Darwin's own studies
of geology)
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3. The earth must be very, very old.
Over very great periods of time, "good"
characteristics have time to accumulate
and less fit ones have diminished.
Homologous vs.
analogous structures vs.
Vestigial structures
Evolution
Macroevolution:
Changes ABOVE the
species level
Microevolution:
Change in the genetic
makeup of a population
Gene pool
Can remain
constant
(equilibrium)
Can change
Variation
Within populations
Polymorphisms
Between populations
Geographic variation
(clines)
Evolutionary fitness
Darwinian vs. relative fitness
 Altering frequency
of phenotypes
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Preservation of Genetic Variation
Diploidy
 Balanced polymorphism
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Heterozygous advantage (sickle cell trait)
Frequency dependent selection (fitness declines
if a characteristic becomes too common)
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Common moths at a disadvantage since the jays
recognized it quickly
Neutral variation

Mutations arising in noncoding regions,
pseudogenes, or parts of a coding region may
not be selected for or against
Sexual selection
Sexual dimorphism arises since they
influence mating success (not
REPRODUCTIVE success)
 Intrasexual vs. intersexual selection (mate
choice)
 Advantage/disadvantages of sex?
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Preservation of allele frequencies
Hardy-Weinburg Theorem
Allele frequencies remain constant from
generation to generation if only Mendelian
inheritance is at work (segregation and
recombination)
 H.W. equilibrium – Population state in
which allele frequencies are not changing,
so genotype frequencies can be predicted
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Conditions for PRESERVING HardyWeinberg equilibrium
Large population size
 No gene flow
 No new mutations
 Random mating
 No natural selection
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The goal of natural selection?
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Evolution is limited by its
ancestry
Adaptations are often
compromises
Chance and natural selection
interact (natural selection is not
random)
Selection can only edit existing
alleles (new alleles do not arise
ON DEMAND)
Small genetic changes can result
in large morphological changes
Anagenesis vs. Cladogenesis
Evolutionary theories
must explain how new
species form
(macroevolution) in
addition to evolution
of adaptations in a
population
(microevolution)
 Adaptations ABOVE
the species level can
help define higher
taxa
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What is a species?
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More importantly
what evidence do
we use to
distinguish species
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Reproductive
isolation
Read through the following definitions of a
species: biological, morphological,
paleontological, ecological, phylogenetic
 Discuss as a group which one you think
should be used when classifying species
and why
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Allopatric speciation
Sympatric
speciation
Adaptive radiation
Punctuated equilibrium
Small genetic changes can result in large
morphological changes
Small genetic changes can result in large
morphological changes
Species selection
Phylogeny and Systematics
Problem: Organism classification and
evolutionary history
 Phylogeny: “tribe” “origin”: Evolutionary
history of a species or group of species
 Evidence:
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Fossil record
systematics (analytical approach using
morphological or biochemical similarities)
Molecular biology represents best method for
VERY closely related species
Sorting homology from analogy
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Example: Bat and birds have wings. Is this the
result of divergent evolution (homologous
structure) or convergent evolution (analogous
structure)?
We need to example the actual bone structure
and complexity of it
Homoplasies: analogous structures that evolved
independently
Molecular homologies and molecular clocks
Sequences must first be
aligned (problem with
deletion mutations?)
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Problems with molecular
systematics?
Molecular homoplasy
Molecular clocks
Calibration: Graph number of nucleotide
differences against known evolutionary
branch points (fossil record)
 Neutral theory
 DNA coding for rRNA vs. mtDNA
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Classification
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Binomial: genus + specific
epithet
Homo sapiens
Taxon (plural taxa): A
taxonomic unit
Phylogenetic trees
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A branched diagram
that depicts the
evolutionary
hypothesis
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Cladograms
Depicts pattern of shared
characteristics but not
evolutionary history
If shared characteristics due
to homology, then it is the
basis of a phylogenetic tree
Origin of Life
Evidence supports this sequence of events
that led to life on earth…
 1. Abiotic synthesis of small organic
molecules
 2. Joining of monomers to form polymers
 3. Packaging of polymers to form
“protobionts”
 4. Origin of self replicating molecules that
made inheritance possible
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1. Abiotic synthesis of organic
molecules
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First conditions on earth
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Lot’s of water vapor
(eventually condensed to
form oceans)
N2, nitric oxides, CO2,
CH4, NH3, H2, H2S
Reducing atmosphere with
energy from UV rays and
lightning (postulated by
Oparin and Haldane in
1920’s
Oceans were a “primitive
soup” of organic molecules
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Current conditions on earth
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Mostly N2, CO2, and O2
O2 comes primarily from
biological splitting of water in
cyanobacteria
Evidence: Stromatolites (3.5
billion years old)
Oxidizing atmosphere
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1. Abiotic synthesis of organic
molecules
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Miller-Urey
experiments
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2. Abiotic synthesis of
polymers
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3. Formation of protobionts
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Chains of amino acids can
form spontaneously on hot
sand, clay, or rock
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Aggregates of abiotically
produced molecules
surrounded by a
membrane
“Laboratory” evidence:
When lipids or other
organic molecules are
added to water liposomes
form, which can do all the
functions of a cell
membrane (shrink and
expand, transport
materials, carry a voltage)
4. Origin of self replicating molecules
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Chech and Altman: RNA plays
catalytic role in protein synthesis
and can carry out enzymatic like
reactions (ribozymes)
Diversity and selection of RNA
molecules
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Dyson:
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Possible scenario
Other scenarios?
Fossil and geology records
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Radiometric dating
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Index fossils (order
in which fossils were
laid down, but not
age)
Based on decay of
radioactive isotopes
Half-life: # of years it
takes for 50% of
material to decay
A brief history of life
Kingdom classification