Transcript Mader 11 ch 15-18 Evolutionary Biology

Summary Evolutionary Biology
Selected Topics from Textbook Chapters:
•
•
•
•
Chapter 15 Darwin and Evolution
Chapter 16 How Populations Evolve
Chapter17 Speciation and Macroevolution
Chapter 18 Origin and History of Life
Read those chapters of the textbook.
Read appropriate sections in Cliffs AP Book
Evolution Topics Overview
• 1. Early Evolution of Life
– Current biological models for the origins of biological
macromolecules.
– Current models for origins of prokatyotes and eukaryotes.
• 2. Evidence of evolution
– Types of evolution that support an evolutionary view of life.
• 3. Mechanisms of evolution
–
–
–
–
Role of natural selection
Heredity and the process of evolution.
Mechanisms of speciation and macroevolution.
Patterns of evolution and their mechanisms.
Evolution
• Gaining perspective on earth and its Life forms
–
Perspective: http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html
– 4500 Million (4.5 Billion) years ago - earth formed (short video
)
– 3500 Million (3.5 Billion) years ago – oldest known fossil (prokaryote)
– 2500 Million (2.5 Billion) years ago – oxygen accumulates in atmosphere
– 1500 Million (1.5 Billion) years ago – oldest known eukaryotic fossil
http://www.history.com/shows/how-the-earth-was-made/videos/playlists/exclusives#the-age-of-earth
– 208 Million years ago – first mammals and first dinosaurs appeared
– 2-6 Million years ago – first hominids appear
(Faces of our ancestors
http://news.discovery.com/human/evolution/early-human-ancestors-faces.htm pictures)
Interactive Timeline
Evolution
• Chronology of the Earth
– From:
–
–
http://garage.physics.iastate.edu/astro2
50/timeline.html
Cambrian Explosion..\..\Biology\Biology
Clipart Movies Animations
Sounds\Biology movies\evolution pbs
cambrian life 24 sec video QT.mov
Genetics of
Evolution..\..\Biology\Biology Clipart
Movies Animations Sounds\Biology
movies\evolution pbs Genetics Tool Kit
Video QT 4 min.mov
Major Differences charts
pages 502-503 Mader
How the Earth Began Movie from
the History Channel (45 min)
How The Earth Was Made: Birth of
the Earth
Movie from National Geographic
(45 min)
Early evolution of life
• models for the origins of biological
macromolecules
– No one knows for sure, these are possible scenarios:
• Meteor “seeded” the earth with organic particles or
(panspermia)..
• Scientific theory: Atmospheric conditions were such that organic
4 andmaterial
¾ pound
(6” have
x 4” xbeen
3”) meteorite
in Antarctica
could
formed ondiscovered
earth. Theory
shown toinbe
1983,possible
believedbytoStanley
have been
formed
on Mars (spontaneous
about 4.5 billion years
Miller’s
experiments
ago. generation).
Fell to earth about 13,000 years ago. Found what could be
fossilized
rod shaped
bacteria.
more
info see:
– Early
atmosphere:
waterFor
vapor,
nitrogen
(possible ammonia at
hydrothermal sea vents), carbon dioxide, small amounts of carbon
http://www.lpi.usra.edu/lpi/meteorites/The_Meteorite.html
monoxide and hydrogen (a reducing environment-good for putting
organic molecules together). Very minimal oxygen.
• Non scientific theory - They were created by some “higher
being”
Early evolution of life
• Miller’s Experiment 1953
– Tried to recreate the conditions on early earth.
– Produced a variety of amino acids and organic
molecules – lent support to the spontaneous
generation theory.
– Many are not convinced – creationists etc.
Early evolution of life
• How do we get from single amino acids to cells?
– Evolution of polymers
• Under the conditions of hydrothermal vents on ocean floor
(high temperature, iron-nickel-sulfide acting as a catalyst)
amino acids can form peptide bonds. Weachtershauser and
Huber experiments.
• Sidney Fox proposed that amino acids could form peptide bonds
abiotically if exposed to dry heat (sun). Amino acids might have
accumulated on the shores of oceans and then been exposed to
the sun, thus forming proteinoids (small polymers with some
catalytic activity). Fox’s theory is a “protein first theory”.
• Graham Cairn-Smith proposed that proteins and RNA arose
at the same time in beds of clay (which contains iron and zinc
and collects energy from radioactive decay).
• Cech and Altman proposed that RNA arose first. Showed
ribozomes capable of being an enzyme and a substrate. (Nobel
Prize 1989).
Early evolution of life
Regardless of how the early organic molecules
(prebionts) originated, they evolved through chemical
selection, and they still lacked the ability to reproduce
and could not be considered to be cells or to be alive.
• Need to develop the means of storing and using energy
• Need to develop a way to reproduce and pass genetic
information to offspring.
Early evolution of life
• Evolution of a Cell
– One proposed mechanism of
protocell development:
• Proteinoids return to water to form
microspheres, which were made of
all protein, but had many qualities of
a cell.
• Microspheres exposed to lipids –
lipids will surround microspheres and
create a protein – lipid membrane.
• Under the right condition (temp,
ions,pH) macromolecules tend to
become coacervate droplets.
• Coacervate droplets absorb and
incorporate substances from their
surroundings into themselves.
Early evolution of life
• Protocells acquire energy
– May have taken in preformed food (possibly preformed
ATP).
– May have used membrane bound hydrogen ions pumps,
these later could evolve to include electron transport
systems.
– Most likely heterotrophs (as above) or chemosynthetic
(such as found around hydrothermal vents). As
atmosphere began to contain more oxygen,
autotrophs(photosynthesis) had an advantage.
– As supply of external ATP dwindled, bacteria that could
use other sources for energy became more prominent.
– Eventually glycolysis became the common metabolic
pathway of all living things (over millions of years).
Early evolution of life
• Protocells reproduce
– Theories on how DNA evolved vary depending on whether:
• Proteins evolved first or
• RNA evolved first or
• RNA and proteins evolved at the same time
– First genes may have been RNA
• This would resolve the question of which came first, the DNA or
enzymes (proteins).
– Eventually, DNA became the prominent genetic material.
Early evolution of life
• models for origins of prokatyotes and eukaryotes
– Protocell evolves into prokaryote.
– 2 –3.5 billion years ago, prokaryotes dominated evolutionary
history.
– Oldest fossil evidence found in stromatolites (fossilized mats of
microbial growth)-dates back 3.2 billion years.
– Lots of metabolic diversity in prokaryotes even 3 billion years
ago.
– Photosynthetic prokaryotes (cyanobacteria) probably evolved
about 2.7 billion years ago.
• Beginning of increase in oxygen in atmosphere
• May have started to kill off some heterotrophs
Early evolution of life
• models for origins of prokaryotes and eukaryotes
– For 2 billion years, prokaryotes are the only living things.
– Oldest eukaryotic fossils are from 1.5-2.2 billion years
ago.
– Possible
Endosymbiotic
theory attempts
explain
they may
early unicellular
600tomillion
yearhow
old fossil
have
evolved.
eukaryote
fossil
of multicellular cup
shaped
eukaryote
found
– First eukaryotes were unicellular,
took
another
million
in Canada in 1999.
years for multicelled organisms to
evolve.
• Have found fossilized multicelled alga that is 1.2 billion years old.
Early evolution of life
• Review of early evolution
– How many biologists believe life may have evolved
• 1. There was abiotic synthesis of small organic molecules such as
amino acids and nucleotides either in the atmosphere or at
hydrothermal vents.
• 2. Monomers joined to from polymers either on land (warm seaside
rocks or clay) or at the vents. First polymers may have been protein or
RNA or both at same time.
• 3. Aggregation of polymers inside a membrane produced a protocell,
which had some enzymatic properties such that it could grow.
Protocells developed in/near the ocean were heterotrophs. Protocells
developed at vents were chemoautotrophs.
• 4. A true cell had evolved once the protocell contained DNA. The first
genes may have been RNA, but later DNA became the information
storage molecule.
•
PBS site DeepTime Interactive Chart http://www.pbs.org/wgbh/evolution/change/deeptime/index.html
Evidence for evolution
• Support for evolutionary view of life comes from:
–
–
–
–
Fossil evidence
Biogeographical evidence
Anatomical evidence
Biochemical evidence
Evidence for evolution
• Support for evolutionary view of life comes from:
– Fossil evidence
• At least 10,000 years old, include bones, casts of plants in shale,
insects imbedded in tree resin (amber)
• Show a succession of life forms over time.
• Some fossils can supply transitional links, such as Caudipteryx
supplying a link between dinosaurs and birds.
• Some fossil records are complete enough to trace back an entire
family tree. Example modern horse Equs.
• Fossils show that as many as 99% of “offshoot” species become
extinct.
Discovered in 1998 in China and said to be evidence of dinosaur-bird link.
Skeletal evidence includes similarity in breastbone, three toed feet, hollow
bones, and swiveling wrist joints. Artists rendition of Caudipteryx on right.
Evidence for evolution
• fossils
Evidence for evolution
• Support for evolutionary view of life comes
from:
– Biogeographical evidence
• Biogeography is the study of plants and animals throughout
the world.
• Related forms evolved in one locale and then spread out to
other areas if accessible. Geography can limit that
spreading.
• Species diversify as they spread.
• Regions suitable to a species may not have any of that
species if there was no way for it to get there.
All of these marsupials are thought to have descended from a common ancestor that entered
Australia 60 million years ago. Each has diversified to suit its environment.
Evidence for evolution
• Anatomical evidence
– Similarities in anatomical structure suggests a common ancestor.
– Homologous structures
• Structures that are anatomically similar because they are inherited
from a common ancestor. (human arm, bird wing, turtle flipper)
– Analogous structures
• Structures that share a similar function, but are anatomically
different. (bird wing, insect wing)
• Analogous structures do not point to a common ancestor.
– Vestigal structures
• Anatomical features that are fully developed in one species but are
reduced or non functional in another species. (human tail bone,
ostrich tiny wings).Point to a common ancestor.
Homologous
structures
– Vertebrates share many
similar
embryological features
• All vertebrates have pharyngeal pouches at some point in their
development. In fish and amphibians, they remain as gills. In
humans they
become
tonsils, thymus and
parathyroid
gland, and
Vestigal
structures
Embryologic
structures
parts of middle ear.
Evidence for evolution
• Biochemical evidence
– Almost all living things share common
biochemicals
• DNA, utilize same 20amino acids and same triplet codes,
many enzymes,ATP
• Functionally, there is no reason why this has to be.
– This points to a common ancestor.
The more similar the sequence of amino
acids is in cytochrome-c, the more closely
related the species are. Human and monkey
only differ by one amino acid.
Mechanisms of evolution
• Natural selection
– Prior to the 1800’s people believed the
earth to be only a few thousand years old.
– Believed species were created perfectly,
“as is” and they were fixed in time.
– Change only occurred by global
catastrophe and repopulation of a newly
created species.
– Charles Darwin and Alfred Wallace and
other scientists began to question those
ideas.
– This was an intellectual revolution and did
not occur without controversy (Scopes
Monkey Trials of 1925). See
http://www.law.umkc.edu/faculty/projects/ftrial
s/scopes/evolut.htm
– Today the theory of evolution and the
mechanism of natural selection have much
evidence to support them.
Mechanisms of evolution
• EVOLUTIONARY HISTORY
– Several camps of thought were being proposed during the
1700-1800s
•
•
•
•
•
•
Carolus Linnaeus
George Loius Leclerc
Erasmus Darwin
George Cuvier
Jean-Baptiste de Lamarck
Charles Darwin
Mechanisms of evolution
• EVOLUTIONARY
HISTORY
– Carolus Linnaeus
• Swedish botanist 17071778
• Father of taxonomy –
binomial nomenclature.
• Only late in his career did
he consider evolution
might be possible.
Do you like my
outfit?
Evolution?
Maybe…
Mechanisms of evolution
• EVOLUTIONARY HISTORY
– George Loius Leclerc (Count
Buffon)
• 1707-1788 French naturalist.
• Wrote a 44 volume set of natural
history encyclopedias that
described all the known plants
and animals!
• Vacillated back and forth
between believing in
evolutionary descent and special
creation and fixation of species.
• Suggested evolution almost 100
years before Darwin’s time, went
very much against the public
opinion of the time.
Here’s some verse from my book, Temple of
Nature (1802), I hope you like it.
Mechanisms of evolution
Organic life beneath the shoreless waves
Was born and nurs'd in ocean's pearly caves;
First forms minute, unseen by spheric glass,
Move on the mud, or pierce the watery mass;
These, as successive generations bloom,
New powers acquire and larger limbs assume;
Whence countless groups of vegetation spring,
And breathing realms of fin and feet and wing.
• EVOLUTIONARY
HISTORY
– Erasmus Darwin
•
•
•
•
1731-1802
Charles Darwin’s grandfather.
Physician and naturalist.
Suggested the possibility of
common descent.
• Offered no mechanism by
which evolution could happen.
• Presented his ideas in verse
sometimes.
Mechanisms of evolution
• EVOLUTIONARY HISTORY
– Georges Cuvier
• 1769-1832 renowned vertebrate
zoologist and comparative anatomist.
• Founded science of Paleontology.
• Staunch believer in creationism and
fixed species.
• Had problems when he found an area
with fossils that showed a succession
of species – hypothesized
catastrophes.
• Catastrophism – a catastrophe would
wipe out one species and god would
repopulate with a new species or new
Cuvier suggested the anatomy of the
species would come from surrounding
mammoth by using a bone. Fossil
areas.
evidence
has agreed with his version.
• Established extinction as a fact.
Mechanisms of evolution
Nobody likes me!
Cuvier is an idiot!
• EVOLUTIONARY HISTORY
– Jean-Baptiste Lamarck
• 1744-1829, never acknowledged in
his time – died in poverty.
• First biologist to believe that
evolution does occur.
• Linked diversity with adaptation to
the environment.
• To explain this adaptation he
suggested the idea that acquired
characteristics could be inherited.
• His theory was wrong (theory of
inheritance of acquired
characteristics has never been
substantiated), but not too far off.
• Lamarck’s longnecks
• Was ridiculed and disrespected by
other scientists – especially Cuvier.
Mechanisms of evolution
• EVOLUTIONARY
HISTORY
– Enter Charles Darwin
• 1809-1882 British naturalist.
• Collaborated with Alfred
Wallace.
• Proposed natural selection
and survival of the fittest
as a means of evolution –
these were revolutionary
ideas.
• Formulated his hypothesis in
1844, but did not present
until 1858 when Wallace told
him of his similar ideas.
Age 45
Age 65
Mechanisms of evolution
• EVOLUTIONARY HISTORY
– Charles Darwin’s Voyage
• 1931 (age of 22) 5 year trip on HMS Beagle – job was (as a
naturalist) to travel with the navy around the world and
expand the navy’s knowledge of natural resources.
• It was also hoped that he would find evidence to support
creationism – that didn't turn out too well!
Mechanisms of evolution
• The ”evolution” of Darwin’s theory of Evolution
– Gathered evidence (before and during his voyage) that
organisms are related by common descent.
• Looked at geological and fossil evidence
• Looked at biogeographical evidence
– See Movie From HHMI (30 minutes)
• Evolution Origin of the Species
Mechanisms of evolution
• The ”evolution” of Darwin’s theory of
Evolution
– Geological and fossil evidence
• Darwin studies books of Lyle and Hutton –
geologists
Whale evolution
• Hutton and Lyle believed that geological
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html
Hummingbird
speciation
3 min always occurring at a slow
changes
were
http://www.pbs.org/wgbh/evolution/library/05/2/l_052_04.html
rate. Continuous cycle of erosion and uplift.
How Does Evolution Really Work 6 min
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
• Lyle proposed a theory of uniformitarianism
Loneliest
Animals
–geographical
Tortoise extinction –changes
50 min
–
slow
occur at a
http://www.pbs.org/wnet/nature/episodes/the-lonelieststeady rate.
animals/introduction/4898/
• These geological principles still believed
today, except the rate is not always
uniform.
• Darwin interpreted this information as
evidence that the earth is very old.
• This would allow enough time for
modification with descent to occur.Agreed
with his fossil evidence.
Mechanisms of evolution
• The “evolution” of Darwin’s theory of Evolution
– Biogeographical evidence
• Biogeography – study of geographic distribution of life
forms on earth.
• Adaptations to environment can cause diversity.
• One species can give rise to many other species that each
adapted differently.
• Darwin observed
–
–
–
–
Patagonian hare vs rabbit and guinea pig
Greater vs lesser rhea
Long neck vs short neck turtles
Finches – observed many different adaptations.
Mechanisms of evolution
• The ”evolution” of Darwin’s theory of Evolution
– Darwin was convinced that adaptations occurred over time (as
opposed to being created “as is” by some higher being).
– He needed a mechanism by which this could happen.
– Both Darwin and Alfred Wallace proposed natural selection as
that mechanism.
Charles Darwin
Alfred Wallace
Natural
Selection
Looks like these two had a
common ancestor!?
Mechanisms of evolution
• The “evolution” of Darwin’s theory of Evolution
– Mechanisms of Natural Selection (Darwin’s Postulates)
• If these conditions met:
– Members of a population have variations (random mutation, meiosis,
crossing over).
– These variations are heritable.
– In a population, many more individuals are produced than the
environment can support.
– Some individuals have adaptive characteristics that enable them to
survive and reproduce better than other individuals (they are more fit
survival of the fittest).
• Then these things can happen:
– An increasing number of individuals in succeeding generations have
the adaptive characteristic.
– The result of natural selection is a population that is adapted to its
environment.
Mechanisms of evolution
• Peppered Moths – an example of Natural
Selection?
– Peppered moth lived in pre-industrial England.
•
•
•
•
All moths were gray with dark flecks.
Rarely a black moth was seen (a variation caused by random mutation).
Both blacks and grays were the same species and could reproduce together.
Which moth would have the advantage when resting on tree bark?
Pre industrial tree bark color.
http://www.utm.edu/~rirwin/moth.htm
Mechanisms of evolution
• Peppered Moths – an example of Natural Selection
– Trees in industrial areas began to change color due to the soot.
• Which moth has the advantage in these areas?
How would the moth population in
the industrial areas look after several
(see next
slide)Live
Some scientists argue thatgenerations?
the “Peppered Why?
Moth” example
is flawed.
peppered moths are very seldom seen resting on tree trunks in daylight.
Argue that the evidence does not support the theory. Maybe the peppered
moth is not a good “classic” example of evolution to teach.
Mechanisms of evolution
• Peppered Moths – an example of Natural Selection
– According to Darwin’s postulates of natural selection:
• not all young produced in a generation survive to reproduce -- many
more moth eggs are produced than can survive; many moths will be
eaten by birds before they reproduce.
• there is variation among individuals -- some are black in color, others are
gray .
• the variation is genetic(heritable) -- black moths have different alleles for
color than do gray moths.
• the different forms differ in fitness -- in industrial environments, black
moths survive to reproduce better than do gray moths since gray moths
get eaten by birds.
– Note that the individual doesn’t change – the population does.
• It is possible over time for these two types of moths to develop into two
different species.
Mechanisms of evolution
• Types of natural selection
– Most traits on which natural selection act are
polygenic (controlled by more than one set of
alleles located at different loci)
– Usually a range of phenotypes – make a bell
shaped curve.
– Types of natural selection:
• Directional
• Stabilizing
• Disruptive
Mechanisms of evolution
• Types of natural selection
– Directional selection
• An extreme phenotype is favored and distribution curve
shifts in that direction. Change occurs as environment
changes.
– Peppered moths
– Antibiotic resistance
» Chloroquine resistance of Plasmodium vivax
(malaria)
» Mosquito resistance to DDT
– Horses increasing in size over time.
Mechanisms of evolution
Mechanisms of evolution
• Types of natural
selection
– Stabilizing selection
• Intermediate phenotype is
favored
• Improves adaptation of
the population to aspects
of the environment that
remain the same.
– Example – human birth
weight
Mechanisms of evolution
• Types of natural selection
– Disruptive selection
• Two or more extreme
phenotypes are favored over
the intermediate
– Example – British land snail
» Has a wide range of
habitat
» Low vegetation areas
favor light banded shells
– birds eat dark banded.
» Forests favor dark
banded shells – birds eat
light banded
Mechanisms of evolution
• Artificial Selection
– Humans often practice artificial selection by
These
plants are
all breeding
derived fromof
one
species,
Brassica oleraceathat
.
causing
the
only
animals/plants
a) Chinese
cabbage
b) Brussel
sprouts
c) Kohlrabi
have characteristics
desired
by humans.
Mechanisms of evolution
– Darwin began his writing on
theories in 1936 after his return
from his voyage. Continued
collecting evidence for the next 20
years.
– Did not publish his ideas until
1858.
• Origin of Species 1859
• Also published:
– Voyage of the Beagle 1845
– Descent of Man 1871
Mechanisms of evolution
• Heredity and the process of evolution
– Population = all the members of a particular species
occupying the same space at the same time.
– Microevolution = small changes that occur within a
particular population over a short period of time.
– Gene pool = all the genes held by that population.
– Population genetics describes the frequency of genes within
a population.
• Can use a special Punnett Square or the Hardy-Weinberg Law
of Equililbrium equation to determine gene frquency.
Mechanisms of evolution
• Heredity and the process of evolution
– Determining gene frequencies
• Sample population: 100 Drosophila
– ¼ homozygous dominant for long wings LL
– ½ heterozygous Ll
– ¼ homozygous recessive for short wings ll
Therefore the
frequency
of thehas
allele25
L inLL,
the50
population
• Therefore
this
population
Ll, 25 llis
100/200
= 50%.
Frequency
of l allele
is 100/200
= 50%
. l, in the
• What
is the
number
of the
L and
thealso
allele
population?
Number of L alleles
Number of l alleles
LL (2L x 25) = 50
Ll (1L x 50) = 50
ll (0L)
=0
LL (0 l)
=0
Ll (1 x 50) = 50
ll (2l x 25) = 50
100
100
Mechanisms of evolution
• Heredity and the process of evolution
– Using a Punnett Square to determine gene
frequencies
• Assuming random matings, what would be the gene
frequencies of the next generation?
• Use the possible egg and sperm combinations of the
population and not the individual. (Data from previous
slide)
Mechanisms of evolution
• Heredity and the process of evolution
– Tells us that sexual reproduction alone cannot
bring about a change in gene frequency.
– Dominant allele need not increase from
generation to generation. Dominance does not
cause an allele to become more dominant.
– The potential equilibrium of a gene pool was
recognized in 1908 by Hardy (1877-1947) and
Weinberg (1862-1937) .
Hardy
Weinberg
Mechanisms of evolution
• Heredity and the process of evolution
– Hardy Weinberg Equation
• States that an equilibrium of allele frequencies in a gene pool will
remain in effect each successive generation of a sexually reproducing
population, as long as these five conditions are met:
– 1. No mutations: allelic changes do not occur, or changes in one
direction balanced by changes in the opposite direction.
– 2.. No gene flow: migration of alleles into or out of the population does
not occur. No immigration of emigration.
– 3. Random mating: pair by chance.
– 4. No genetic drift: the population is very large, and changes in allele
frequency due to chance alone are insignificant.
– 5. No selection: no selective agent favors one genotype over another.
• Are these conditions likely to be met?
• So what good is this formula?
– Tells us what factors cause evolution(opposites of the five listed
conditions)
– Use equation as a baseline to measure whether evolution has occurred.
Frequency of each allele
P+q=1
Frequency of genotypes
p2 + 2pq + q2 =1
Do Practice Problems 1
Questions #1 and 2 on
page 303 of textbook.
Mechanisms of evolution
• Heredity and the process of evolution
– Causes of (Micro)evolution
•
•
•
•
Genetic mutations
Gene flow
Nonrandom matings
Genetic drift
– Bottleneck effect
– Founder effect
• Natural selection (only one that results in adaptation
to the environment)
– Non random matings
• Inbreeding
Mechanisms of evolution
• Heredity and the
process of evolution
– Genetic mutations
• Raw material of evolution.
• Cause many alleles in the gene
pool to have multiple alleles.
– Gene Flow
• = genetic migration
• Movement of alleles between
populations by migration and
breeding of individuals.
• Initially adds variety but then,
• Tends to decrease genetic diversity
of the two groups over time.
– Does not change allele frequency in a population, but does
lead to a higher % of homozygotes at all gene loci.
– Inbreeding in humans increases the frequency of recessive
abnormalities.
• Assortive matings
– Same phenotypes breed  increased number of individuals
homozygous for that trait.
– Sexual selection
» Female chooses a particular male phenotype to
breed with.
– Genetic Drift
• Change in gene pool allele frequency due to chance.
• Random, not affected by environment.
• Small populations more likely to lose an allele.
– Bottleneck effect
» Some incident leaves only a small number of the
population alive to reproduce.
– Founder affect
» Rare alleles occur at a higher frequency.
Mechanisms of evolution
• Mechanisms of speciation and
macroevolution
– Speciation = splitting of one species into two or
more species, or the transformation of one
species into another over time.(several different
methods)
– Speciation is the final result of change in gene
pool allele and genotype frequencies.
– What is species?
• A population that interbreeds and has a shared gene
pool. Each species is reproductively isolated from every
other species.
Reproductive Isolating Mechanisms
Example
Mechanisms of evolution
Isolating mechanism
Prezygotic
Species at same locale occupy
different habitats.
Habitat Isolation
• Mechanisms of speciation
and at different
Species
reproduce
Temporal Isolation
seasons or different times of day.
macroevolution
Behavioral Isolation
In animals, courtship behavior
differs, or they respond to
different songs, calls,
mechanisms
pheromones, or other signals.
– Mechanisms of speciation:
• Reproductive isolating
– Pre zygotic
– Post zygotic
Mechanical Isolation
Genetalia unsuitable for one
another.
Postzygotic
Gamete Isolation
Sperm cannot reach or fertilize
egg.
Zygote Isolation
Fertilization occurs, but zygote
cannot survive.
Hybrid Sterility
Hybrid survives, but is sterile and
cannot reproduce.
F2 Fitness
Hybrid is fertile, but F2 hybrid has
reduced fitness.
Mechanisms of evolution
• Patterns of Evolution
– Modes of speciation
•
•
•
•
Allopatric speciation
Sympatric speciation
Divergent evolution
Convergent evolution
Terms to Know
for AP TEST
Mechanisms of evolution
• Allopatric speciation
– Populations geographically isolated from each other – gene
flow stops.
– Adaptive radiation
» Type of allopatric speciation
» Several different species develop rapidly from one
ancestor due to environmental pressures. (example
Hawaiian birds)
Allopatric speciation
Two populations experience gene
flow.
Gene flow is interrupted by a
geographical barrier. Variant types
occur
Drift and different selection
pressures cause divergence
between isolated gene pools.
Reproductive isolation is present
even though geographical barrier
has been removed. Speciation is
complete.
Adaptive radiation
• More than 20 species evolved from a single species.
Mechanisms of evolution
– Sympatric speciation
• Population develops into two or more species without
prior geographic isolation.
• Often occurs in plants
– Plants often polyploid – leads to reproductive isolation
Sympatric speciation
One population.
Reproductive
isolation and
speciation occur in
a single
generation.
Drift can cause
further divergence
between isolated
gene pools that
experience same
selection
pressures.
Mechanisms of evolution
– Convergent evolution
• Process in which organisms that are not related become
more similar in one or more characteristics because of
independent adaptation to similar environments.
– Ex.-whales and fish have fins and streamlined bodies, but do
not share a common ancestor.
– Divergent evolution
• Closely related species develop different behaviors and
traits, may ultimately become separate species.
– Ex. – the peppered moth
• LUCY
–
“Discovered by Donald Johanson (curator at the
Cleveland Museum of Natural History at
the time) and Tom Gray in 1974 at Hadar in
Ethiopia (Johanson and Edey 1981; Johanson
and Taieb 1976). Its age is about 3.2 million
years. Lucy was an adult female hominid of
about 25 years. About 40% of her skeleton was
found, and her pelvis, femur (the upper leg
bone) and tibia show her to have been bipedal.
She was about 107 cm (3'6") tall (small for her
species) and about 28 kg (62 lbs) in weight.”
–
http://www.talkorigins.org/faqs/homs/lucy.html
Whale evolution
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_
05.html
Hummingbird speciation 4 min
http://www.pbs.org/wgbh/evolution/library/05/2/l_052_
04.html
How Does Evolution Really Work 6 min
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.h
tml
Loneliest Animals – Tortoise extinction – 50 min
http://www.pbs.org/wnet/nature/episodes/the-loneliestanimals/introduction/4898/
Short video: http://sexyarchaeology.org/?tag=sexy-archaeology
1994 Ardi discovered in Etheopia. Dated 4.4 million years old.
http://dsc.discovery.com/tv/ardipithecus/handbook2/handbook2.html
The End