Transcript Evolution - Clark Pleasant Community School Corp

Evolution
Just a “Theory?”
Evolution
• Genetic change in
species through time
• Microevolution: a
change in a
population’s allele
frequencies
• Macroevolution: large
scale patterns, trends
among larger groups
Is God Involved?
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•
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It depends on who you ask!
Atheistic evolution: does not believe in God
Nontheistic evolution: divorce the two ideas;
believe in God, but believe that God has nothing
to do with evolution; scientific approach is
separate.
Theistic evolution (gradual creation): creator was
responsible for the initial creation event, but then
“hands off.”
Progressive evolution: creator is playing a role in
directing evolution; guides it (implies a goal)
Quick creation (Scientific Creationism”): believe
in the biblical account of creation. (Genesis)
Craig Nelson, Indiana University
Darwin’s Theory
• Variation already exists
within a species
• Scarcity of resources leads
to competition
• Only the “fittest” survive
to reproduce
• Natural selection:
organisms with favorable
variations survive and
reproduce
Darwin’s Theory
• Natural selection can lead to the formation of new
species
• Implies that many species once shared a common
ancestor
• Adaptive radiation: where many species evolve from
one
Change in gene frequency
• A population contains
variation: same traits, but
different alleles.
• A given allele may
become more common,
less frequent, or stay the
same.
• So differences from point
A to B on a time line can
occur
Change over time
• Populations can
evolve—
individuals
cannot evolve!
How do Gene Frequencies
Change?
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Mutation
Gene flow
Genetic Drift
Natural selection
• There is not a goal, as some cartoons depict
Evidence of Evolution
• Fossil
• Comparative anatomy
• Homologous structures
analogous structures
vestigial structures
• Comparative embryology
• Biogeography
• Comp biochemistry
Fossil evidence
• Deepest layers of rock
are the oldest
• Can trace the changes
that occurred in some
species over time
• Not all species are
fossilized
Comparative Anatomy
• Homologous
structures: similar in
skeletal structure
• May look different on
the outside
• May vary in function
Comparative Anatomy
Suggest a common ancestor
Homologous Structures
Homologous Structures
Whale
metacarpals are
similar to our
knuckle bones
Whale phalanges are
similar
W to our finger bones
h
a
Vestigial Structures
• Structures or organs that
appear to serve no purpose
• Examples: human
tailbone, appendix
• Often homologous to
structures that are useful
in other species
• Suggest common ancestry
Comparative Embryology
• Embryos of certain
species develop almost
identically, especially
in the early stages
• Similar genetic
instructions
• Suggests that
organisms descended
from common
ancestor
Biogeography
• Same environments in
different parts of the
world yield different
organisms
• Ostrich, rhea, emu
Biogeography
Comparative Biochemistry
• Complex biochemical
compounds such as
cytochrome c,
antibodies, and blood
proteins are almost
identical in many
species
• Suggests high degree
of relatedness and
common ancestry
Microevolution
Changes occur in a population’s allele
frequencies over time.
Microevolution
• Individuals in a
population have same
number and kinds of
genes
• But forms of the gene
may vary (alleles)
• Each individual is
unique because of his
combination of alleles
Microevolution
• One allele may be
more or less common
than others.
• One or more alleles
may disappear
• One or more alleles
may become more or
less common
Causes of allele frequency
changes
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•
•
•
•
Recombination
Mutation
Gene flow
Genetic drift
Natural selection
• All these shuffle the
alleles
Recombination
• Creates new genetic
varieties
• Sperm and ovum both
bring 23 chromosomes
• Resulting in a zygote
with a new
combination of
chromosomes distinct
from either parent
Mutation
• Heritable change in
the DNA
• Can be helpful,
harmful, lethal, or
neutral
• Can cause changes in
the individual’s ability
to survive and
reproduce
Gene Flow
• Genes are transferred
from one population to
another.
• Migration
• People travel to
another area and
successfully mate with
the population there.
Genetic Drift
• In small, reproductively isolated populations,
chance can change the gene frequency.
• The smaller the population, the more dramatic the
change
Genetic Drift
• Very pronounced
after a bottleneck
• A severe reduction
in population results
in only a small
population
surviving
• Gene frequencies
are altered
• Page 288-289
Natural Selection
• Usually the most
important mechanism
of evolution
• Environment selects
the individuals with
the best suited
genotypes for survival
and reproduction
Natural Selection
• For natural selection
to cause evolution, it
must select for or
against one or more
genotypes for a trait
• AA Aa
aa
• AA and aa
• AA or aa… and so on
Frequency drops, but not to 0.
• The a will never completely disappear as long as there are
heterozygotes (Aa)
• It is not a disadvantage to the heterozygote
Selection against one of the homozygotes (aa)
Expected
offspring genotypes
Possible
parent mating
patterns
AA
AA X AA
4
AA X Aa
2
2
Aa X AA
2
2
Aa X Aa
1
2
1
6
( 38% )
1
( 6%
Total
9
( 56% )
Aa
aa
Selection against aa
Directional Selection
• Allele frequencies
tend to shift in a
consistent direction
• In response to the
environment, or a new
mutation gets it started
• One end of the range
becomes more
common than the
midrange
Peppered moth
example; page 282
Stabilizing Selection
• Intermediate forms are
favored.
• Tends to counter
mutation, gene flow,
and genetic drift
• Could favor the
heterozygote
• Page 284
Disruptive Selection
• Forms at both ends of the range are favored;
the intermediate forms are selected against
• Page 285
Speciation
An example of microevolution
What is a species?
• A species consists of
organisms that can
interbreed and produce
fertile offspring
• A horse and a donkey
can interbreed to
produce a mule, but
the mule is not fertile
New species emerge…
• As a result of
reproductive isolation
• As a result of
geographic isolation
• Populations become
cut off from each
other, and evolve
separately
Reproductive isolation
• Any heritable feature
of body form,
function, or behavior
prevents interbreeding
• Not necessary to have
a physical separation
• Prezygotic or
Postzygotic
• Pages 294-295
Geographical isolation
• Physically separated
• Could by mountains,
river, body of water
separating islands, etc.
Geographical isolation
• Allopatric speciation:
a physical barrier
intervenes between
populations and
prevents gene flow
among them
• Hawaii, Galapagos
Islands, Florida Keys
Sympatric Speciation
• A species may
form within the
home range of an
existing species
• No physical
barrier
Parapatric Speciation
• Neighboring
populations become
distinct species, while
maintaining a hybrid
zone
Bullock’s oriole range
Baltimore oriole range
Adaptive Radiation
• A burst of different species from a single lineage
• May be due to physical access to a new habitat or
• Key innovations may permit better survival
Classification
Five or six kingdoms?
The Old 5 Kingdom System
The Old 5 Kingdom System
• All the bacteria were grouped into Kingdom
Monera
• Monera included eubacteria and archaebacteria
New relationships discovered
• In the 1970’s, with
better methods to
analyze biochemical
makeup and sequence
DNA, huge
differences emerged
between eubacteria
and archaebacteria
Differences emerge
• Archaebacteria live in
harsh environments
• Subdivided into three
groups bases on
habitat: methanogens,
thermoacidophiles,
and extreme
halophiles
Archeabacteria
• Methanogens are
anaerobic, and are
found in swamps,
marshes, sewage
treatment plants,
digestive tracts
• Produce methane
Archeabacteria
• Extreme halophiles
live in very salty water
• Use salt to generate
ATP
• Found in Dead Sea,
Great Salt Lake
Archaebacteria
• Thermoacidophiles
live in extremely hot
and acidic water
• Temp of 110 C, and
pH of 2
• Hot springs, volcanic
vents, cracks on ocean
floor that leak scalding
water
The New 6 Kingdom System
Higher organisms are more closely related to the
archaebacteria than to the eubacteria.
Showing relationships
• Phylogeny:
evolutionary
relationships between
species, starting with
ancestral forms and
showing branches
leading to descendants
Showing relationships
• Phylogeny can be
shown in an
evolutionary tree or a
cladogram
Showing relationships
Showing relationships
Taxonomy
• Identifies, names and
classifies species
• Binomial system
• Scientific name is
Genus species
• Homo sapiens