Transcript Divergent evolution

CHAPTER 15
EVOLUTION
EVOLUTION IS CHANGE IN
SPECIES OVER TIME
 Orderly succession of
changes.
 Change of
populations of
organisms over
generations.
 Fossil record shows a
modification process
at work.
EVIDENCE SUPPORTING THE
THEORY OF EVOLUTION:
1.
2.
3.
4.
5.
The Fossil record
Comparative Anatomy
Embryology
Biochemistry
Real life Examples
1. The FOSSIL record
 Traces of long-dead organisms
(10,000 years old at the least
2B fossil).
 Found in sedimentary rock.
 Examples: cast, mold, or
petrified.
 Robert Hooke 1668 says
they’re not rocks- smarty
pants, not just microscope
dude.
STRATA
successive
layers of
rock
deposited
over
geologic
time.
Geologic History of Earth
The Fossil Record
LAW OF SUPERPOSITION
1. Successive layers of rock or soil
were deposited by wind or water.
2. Lowest STRATUM is the oldest.
3. Top STRATUM is the most recent.
4. Relative or absolute age can be
determined.
5. Patterns of mass extinctions.
5 so far (we are in the 6th)
GEOLOGIC
HISTORY OF EARTH
 ARCHEAN- prokaryotes arise
 PROTEROZOIC- eukaryotes
arise
 PALEOZOIC- marine
invertebrates, fish,
amphibians, reptiles, plants
arise
 MESOZOIC- dinosaurs rule
 CENOZOIC- mammals
DISCOVERIES FROM
THE FOSSIL RECORD
 Earth’s history is more than 100,000 times longer than recorded
human history (4.5 billion NOT 6K years).
 Pattern: species appear-exist-disappear-new arise etc.
 Mass extinctions due to drastic environmental change.
5 so far and we are currently in the 6th one
 Biogeography (studying the global distribution of fossils and
living organisms) shows a logical pattern.
ie. kangaroos only live (Australia) where kangaroo ancestor
fossils are found- Australia.
PANGEA = ALL LAND
ARCHAEOPTERYX
BirdDinosaur
link
2. COMPARATIVE ANATOMY
compare anatomy of species to infer (figure out) evolutionary
relationships.
1. Homologous Structures reveal the pattern of
divergent evolution.
2. Analogous Structures reveal a pattern called
convergent evolution.
3. Vestigial Structures show divergence from
an ancestor.
HOMOLOGOUS STRUCTURES
Are similar
features that
originated in a
common ancestor
that are adapted
and modified for
different
functions.
HOMOLOGOUS
STRUCTURES reveal common
ancestry and a pattern of
evolution called DIVERGENT
EVOLUTION.
ANALAGOUS STRUCTURES
Look-alike structures in unrelated species form as a response to
similar “selection pressures” ex. The fat insulated, streamlined
bodies of penguins (bird), sharks (fish) and dolphins (mammal).
HUMMINGBIRD wings- endoskeleton (bones)
HUMMINGBIRD MOTH wingsexoskeleton… not arms
 Analogous structures reveal a pattern of
evolution called convergent evolution.
 Similar environments selected for superficially
similar adaptations.
Hedgehog, porcupine, echidna all evolved the quills independently.
VESTIGIAL STRUCTURES
are features
that serve no
useful purpose
but show
relationships
to ancestors in
which the
structure
WAS useful.
examples of vestigial structures:
 Tailbone in humans no longer useful because we
don’t have a tail/muscles attached to it. Shows our
primate heritage.
 Blind mole rat eyes (non functional) covered by
layer of skin.
 Human body hair- goose bumps… (hair fluffs up
for insulation or to make the organism look
bigger).
 Penguins and dodo birds have hollow bones
(adaptation for flight) even though they don’t fly.
Embryological development
reveals evolutionary history
3.
E
M
B
R
Y
O
L
O
G
Y
Von Baer- correct simple observation
Embryos of different vertebrate species could not be as
easily distinguished as adults of that species.
Earnest Haeckel- WRONG theory “biogenetic law”
- “ontogeny recapitulates phylogeny”
- development retraces evolutionary history (time
machine)
- sketches exaggerated/ time machine idea crazy.
 Genes that are “common” are expressed (turned on)
early in development.
 Genes that differ (mutations that accumulated in the
different species) are expressed later.
 Modern evidence- Hox genes / developmental pathways.
From Campbell Biology
 Closely related organisms go through similar
stages of development.
 The theory of recapitulation is an overstatement.
 Although vertebrates share many features of
embryonic development- it is not as though a
mammal first goes through a ‘fish stage’, then an
‘amphibian stage’, and so on.
 Ontogeny can provide clues to phylogeny but it is
important to remember that all stages of
development may become modified over the
course of evolution.
4. BIOCHEMISTRY
 COMPARE DNA OR
AMINO ACID
SEQUENCES
 MORE SIMILAR =
MORE RECENT
COMMON ANCESTOR
 DNA mutations occur at a
steady rate. The number of
differences are used to
create a “MOLECULAR
CLOCK” to better
estimate divergence from
common ancestors.
COMPARISON OF DNA SEQUENCES CONFIRM
THE EVOLUTIONARY HISTORIES SUGGESTED
BY FOSSILS AND ANATOMY.
Ex. chimps and humans share 98-99% DNA
5. EXAMPLES
of evolution
… post
The
industrial
revolution
England
changed the
moth’s
environment.
Lichen on tree
bark turned
black from
factory-released
soot & smoke.
Peppered Moth
Industrial melanism
colored moths became more
•The “right stuff” Black
abundant in the population =
(phenotype) used to microevolution.
be the light coloration.
•The “right stuff”
became the dark
coloration phenotype.
•Black moths were
hidden from
predators.
Insecticide resistance
ex. Raid Bug spray on
cockroaches
Few insecticide resistant
mutants survive and
reproduce (preadaptation)
population made mostly of
“resistant” mutants… spray
insecticide
Insecticide ineffectual
at killing insects !
Antibiotic resistant
microbes!
 TB
 Gonorrhea
 Staph
MRSA
 pneumonia
PATTERNS OF
EVOLUTION
1.
Co-evolution
2.
Convergent evolution
3.
Divergent evolution
4.
Adaptive Radiation
5.
Parallel Evolution
PATTERNS OF
EVOLUTION
1. Co-evolution (arms race) organisms “drive”
each other’s evolution
Predator-prey, parasites-hosts, plants-pollinators
2. Convergent evolution (come together) same
environment selects similar phenotypes
(analogous structures) Insect & Bird wings
3. Divergent evolution (go apart) different
environments selects different phenotypes
(homologous structures) your hand and bat wing
4. Adaptive Radiation
divergent evolution of many species
from one common ancestor.
Ex. Galapagos finches, mammals
5. Parallel Evolution
The convergent evolution of species
adapted tot he same way of life after a
divergence occurred.
Ex. Marsupial & Placental mammals… ex.
COEVOLUTION is the change
of two or more species due to their
close interactions.
•Predator-prey
Ex. cheetah-gazelle
•Parasites-host
Ex. viruses-cells
•Herbivore-plant
Ex. tortoise-cactus
•Plants-pollinators
Ex.flowers-moths
CARRION FLOWER SMELLS LIKE ROTTING
MEAT TO ATTRACT IT’S INSECT
POLLINATORS- FLIES
CONVERGENT
EVOLUTION
 Occurs when the
environment selects
similar phenotypes
(forms) even though the
ancestors are quite
different.
 Bird/fish/mammal all
have fat insulated,
stream lined bodies with
flippers.
 Analogous Traits
D
I
V
E
R
G
E
N
T
Divergent Evolution occurs when two or more related
populations become more and more dissimilar- due to
differing habitats…
this RESULTS in NEW SPECIES & Homologous Traits
ADAPTIVE RADIATION OF DARWIN’S FINCHES… much
divergent evolution from a single ancestral species.
Two ideas about
the rate of
speciation…
Either long periods
Of “stasis”
Followed by
Rapid periods of
Evolution
Or
Gradual consistent
Change.
Punctuated Equilibrium
Gradualism
Parallel Evolution… The Placental vs. Marsupial split occurred
Long ago. Nature selected “for” similar adaptations in both
Lineages to fulfill the same niche on separate continents.
EVOLUTIONARY
THEORY:
LAMARCK
“inheritance of acquired characteristics”
DARWIN
“natural selection”
LAMARCK’S
EXPLANATION
•Similar species descended from a
common ancestor.
•ACQUIRED TRAITS were
passed to offspring.
•Acquired traits- determined by
behavior NOT genetics.
•Duck’s webbed feet come from
“stretching” their toes.
•Human’s lost tail because they
“don’t use it”.
•Girraffe’s long neck ‘cause they
“stretched” to reach leaves.
•WRONG & EASILY
DISPROVED
CHARLES DARWIN
“NATURAL
SELECTION”
 Organisms best suited to their
environment reproduce more
than those who aren’t.
 Favorable traits increase in
populations over time.
1. Differences exist between
members of the same species.
2. Competition for resources.
DARWIN’S
INFLUENCES
 UNIFORMITARIANISM
earth undergoes processes
like earthquakes,
volcanoes, erosion,
sedimentation repeatedly.
 Modification of
environments is slow, but
inevitable.
Charles Lyell
Principles of Geology
 Earth is old! 4.5 billion
years not 6 thousand.
5 year H.M.S. BEAGLE voyage to
the GALAPAGOS ISLANDS
GALAPAGOS ISLANDS are relatively young… formed 5 mya
FINCHES
DARWIN’S
OBSERVATIONS
 Earthquake in Chile- land
lifted 3 feet around harbor.
 Marine Fossil Shells in the
Andes Mountains (14Kfeet).
 Galapagos finches (13)
 Galapagos tortoises
 Angrecum Orchid &
pollinator with a long
tongue.
 Thousands of species
observed and documented.
WHAT IS FITNESS???
 Having the “right stuff ” at the “right time”
 Favorable traits give the organism who has it an
ADAPTIVE ADVANTAGE
 HIGH REPRODUCTIVE SUCCESS!!!
 Populations adapt to their environment as the
proportion of favorable genes increase
POPULATION ADAPTED TO HIDE FROM
PREDATORSIN THIS CASE, THE RIGHT STUFF
IS BEING BROWN.
RECAP OF EVENTS
1. 1800ish LAMARCK’s Inheritance of
Acquired Characteristics
2. 1831 BEAGLE VOYAGE
3. 1858 DARWIN’s On the Origin of
Species by Means of Natural Selection
1. Descent with modification
2. Modification by natural selection
TYPES OF NATURAL
SELECTION
TYPES OF NATURAL
SELECTION
 Stabilizing selection
 Directional selection
 Disruptive selection
 Sexual selection
 Artificial selection
STABILIZING
SELECTION
Stabilizing Selection
 eliminates extreme individuals.
 A plant that is too short may not be able to compete
with other plants for sunlight.
 However, extremely tall plants may be more susceptible
to wind damage.
 Combined, these two selection pressures act to favor
plants of medium height.
DIRECTIONAL
SELECTION
Directional Selection
 selects against one extreme.
 In the familiar example of giraffe necks, there was a
selection pressure against short necks, since individuals
with short necks could not reach as many leaves on
which to feed.
 As a result, the distribution of neck-length shifted to
favor individuals with long necks.
DISRUPTIVE
SELECTION
Disruptive selection
 eliminates intermediate individuals.
 imagine a plant of extremely variable height that is pollinated
by three different pollinator insects: one that was attracted to
short plants, another that preferred plants of medium height,
and a third that visited only the tallest plants.
 If the pollinator that preferred plants of medium height
disappeared from an area, medium height plants would be
selected against, and the population would tend toward both
short and tall plants, but not plants of medium height.
Sexual Selection
The evolutionary process is sped up
through ARTIFICIAL SELECTION