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Classification & Evolution
Evolution - Microevolution
A change within the gene pool of a
population over time (changes in
the percentages of alleles)
Lamarck vs. Darwin
The Theory of Evolution
Darwin
Descent with Modification:
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Darwin - Organisms can have offspring that are
modified forms of themselves.
Modern Interpretation – DNA mutations and genetic
recombination through meiosis and fertilization cause
variations within populations
Natural Selection
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Organisms have more babies than can be supported
by the environment
The most successful at surviving and reproducing
pass those genes on and become more numerous in
the population
Therefore, evolution is due to
multiple forms within populations
– if an uncommon form works
better – it will become more
common over time (populations
change over time to what works
the best)
These smaller changes become
bigger over time. The
commonalities among organisms
are evidence of common ancestry.
Selection Factors (Pressures)
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Predator/Prey – ability to get prey or
evade predators
Competition – better competitor for food,
homes, mates
Abiotic Factors (amt. of ppt., wind, type of
soil, amt. of sunlight, temperature)
Sex Selection
The five mechanisms of
evolution – It’s not just Natural Selection
5 Fingers of Evolution - TedEd
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Small population (Genetic Drift) – next
generation doesn’t match probability so get a
change in the allelic frequencies due to chance
Non-random mating – type of selection
Mutation
Gene Flow – things moving in or out of a
population changing the allelic frequencies
Natural Selection – most important and only one
that makes improvements!
Examples of the 5 mechanisms
of Evolution
Natural Selection is the only mechanism
of evolution that creates Adaptations!!
Adaptations:
Genetic traits that allow organisms to survive
better in their environment
Even though natural selection
causes things to generally
improve and become more
adapted to their environment,
evolution doesn’t always create
the “perfect” best adapted forms
if the “perfect” random mutation
doesn’t happen
Why biodiversity remains
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Even though natural selection tends to eliminate
diversity for the best suited forms – diversity is
maintained by:
 Meiosis and genetic recombination
 Heterozygosity
 Continued mutations
 Neutral mutations
 Multiple Selection Factors
 Continuously changing environments
This is important because if environment
changes – there will be a part of the population
or species that can survive
Evidence of Evolution
1. Direct evidence:
 Finches
 Fish
 peppered moths
 Insects
 bacteria
Evidence of Evolution Continued
2. Artificial Selection
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Pigeons
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Mustard Plant
Fossils – see new things and see many
things disappear
Fossil Record – fossils show descendancy –
relatedness matches age of fossils
3.
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Don’t find different vertebrate classes in the same age rock
– appears to happen chronologically
Can find transitional fossils linking ancient and modern
species
See fossils of things that no longer exist and things that
weren’t in the older fossils – appears to be new
Evidence of Evolution Continued
4.
Taxonomy (The Study of Classification)
Shows unity and diversity – everything
seems to be related and modified versions
of each other
Taxonomy –
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the study of classification
Why do we classify things?
Helps us understand how things are related
which helps us understand things in general
Linnaeus came up with a classification system to
better understand living things
The system ended up being a hierarchy
What is a hierarchy?
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Classify shoes with a partner
Is this a hierarchy?
What does it help us understand about
shoes?
What is the classification scheme for living
things like?
The classification system
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Domain, Kingdom, Phylum, Class, Order,
Family, Genus, Species
(Kings play cards on fine green sheets)
The hierarchy shows a unity that all living
things are related and share a common
ancestor (seem to be modified versions of
each other)
It also shows diversity – that they have
changed a great deal over time
Biological Taxa
Example of Classification
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Goes from general to
specific
Continually branches
The longer things stay
together before branching,
the more they have in
common
If two things are in the
same category – they
share everything more
general in common
Taxonomy
All living things have some
things in common
Some have more things in
common and more closely
related
The further down the scheme
they stay together (from
general to specific), the more
traits they share in common
and the more related they are
How do we Classify to show
evolutionary relationships?
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Comparative Anatomy
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Homologous Structures – structurally similar even
though have different functions (shows relatedness
vs. individual engineering)
Vestigial Organs – “left-overs” – no funtion in current
times
Comparative Embryology – the longer in
development things look the same the more related – ex.
all vertebrates go through the same stages early on –
changes in genes and reading of genes causes different
forms
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Biochemistry/Molecular Biology – same DNA in all
organisms – looks like modified copies of each other
(mutations to make different proteins)
Comparative Anatomy
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Analogous structures – similar due to like
environments, built from different structures (ex.
Wings or birds and insects) DO NOT SHOW
RELATEDNESS – NOT USED FOR CLASSIFICATION
Homologous structures – similar due to common
structure and therefore common ancestry (ex. Wing
of bat, whale fin, arm of human, paw of dog)
Use ONLY homologous structures for classification
Problem with comparative anatomy – like structures
not necessarily from common ancestor – may be
shaped by same environmental factors
Homologous Structures
Homologous Structures show evolutionary relationships and
should be used for classification
Analogous structures do not show evolutionary relationship
and are not used for classification
Comparative Embryology
Living things share some common embryological development – the
longer the same, the more related
Comparative Biochemistry
All things show some DNA and protein relatedness – the more DNA and
proteins they have in common – the more closer related.
If they have the same protein, more amino acids in common in the
protein – the more related
Comparative Biochem
If have same proteins, closer their DNA sequences – the more alike
Dolphins are closer related to bats than sharks – can tell
through proteins and DNA that they are more related
Evolution – a step further
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Microevolution – change in the gene pool
within a population (change in allelic
frequencies)
Speciation – creation of new species
Macroevolution – creating all of the
various taxa from a common ancester
Species Concept
Species – organisms that
interbreed and produce fertile
offspring under natural conditions
Speciation – the formation of new
species
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Species concept - Why species remain
distinct:
Habitat Isolation – live in different areas
Behavioral Isolation – mating rituals, firefly
lighting patterns
Temporal Isolation – different mating times
(seasonal), different times of flowering,
nocturnal vs. day
Mechanical Isolation – physically impossible to
mate
Gametic Isolation – gametes can’t match up
Infertility of Hybrids
Speciation –
see the appearance of new species in
fossils – where did they come from?
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Production of new species due to
separation
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migration to different islands
new mountain separates them
lake dries up to multiple little ponds
Separated groups undergo different
mutations
Each separated part of the species is
acted upon by different “selectors” and
eventually become so different that they
can’t or do not any longer interbreed
Examples of Speciation
Why evolution takes places once a
population becomes separated
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Organisms on the edge are usually different
anyway
Small group leaving may not be representative
of whole
More change due to chance in small groups
Neutral mutations may become fixed without
selective pressures due to small population size
Different mutations
Different selective pressures
Therefore: Microevolution over time slowly
changes each population until they are different
species
Macroevolution
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substantial change in organisms
Origin of new phyla, classes, orders,
families
Is it due to the cumulative product of
microevolution or some big event or…????
The appearance of flowering plants seems
to be all at once?????
The appearance of mammals seems to be
all at once?????
Punctuated Equilibrium
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Big changes (episodes of speciation) followed by
slow gradual change (if optimized for
environment – shouldn’t be a lot of change due
to selection unless large change in selection
pressures)
Due to quick geographic separation and genetic
drift
Due to sudden genome changes
Changes may not be shown in fossils
Mechanisms of Macroevolution
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Pre-adaptation – structure is adapted for 1
thing and later used for another function
(gradual change in existing structure leads
suddently to a new function)
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Example – lattice-like bones of birds – some
dinosaurs had it but must have had another
function
Changes in developmental genes
Mass Extinction – due to huge
geographical changes (climate, destruction
of habitats) – leaves it open for species to
fill new places
Mechanisms of Macroevolution
Cont.
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Accumulation of Microevolution not
preserved in fossil record or intermediates
not found due to small numbers
Summary of Macroevolution
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May be due to rapid changes:
Mass separations
Rapidly changing environments
Chromosomal or developing genes
mutating
Mutations acted upon by huge genetic
drift and selection
Mass extinctions causing adaptive
radations
Remaining Questions about
Macroevolution
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Could it really be compounded
microevolution?
What is gradual vs. quick?
What is missing from the fossil record?
Do different mechanisms work at different
levels?