processes of evolution - slhs ap...
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Processes of Evolution
15
How do biologists use evolutionary theory to develop better flu vaccines?
Evolution Is Both Factual and the Basis of Broader Theory
In science, a theory is a well-substantiated,
unifying explanation for a set of verified,
proven hypotheses
Evolutionary theory is the understanding
and application of the processes of
evolutionary change to biological problems.
Applications:
• Study and treatment of diseases
• Development of crops and industrial
processes
• Understanding the diversification of life
Evolution Is Both Factual and the Basis of Broader Theory
Even before Darwin, biologists had suggested
that species had changed over time, but no
one had proposed a convincing mechanism
for evolution.
Evolution Is Both Factual and the Basis of Broader Theory
Charles Darwin was
interested in geology
and natural history.
Evolution Is Both Factual and the Basis of Broader Theory
In 1831, Darwin
began a 5-year
voyage around the
world on a Navy
survey vessel, the
HMS Beagle.
The Voyage of the Beagle
Evolution Is Both Factual and the Basis of Broader Theory
From the observations and insights made on
the voyage and new ideas from geologists
on the age of the Earth, Darwin developed
an explanatory theory for evolutionary
change:
• Species change over time
• Divergent species share a common
ancestor (descent with modification)
• The mechanism that produces change is
natural selection
Concept 15.2 Mutation, Selection, Gene Flow,
Genetic Drift, and Nonrandom Mating Result in Evolution
Many of Darwin’s observations of variation
and selection came from domesticated
plants and animals.
Darwin bred pigeons and recognized
similarities between selection by breeders
and selection in nature.
In both cases, selection simply increases the
frequency of the favored trait from one
generation to the next.
Evolution Is Both Factual and the Basis of Broader Theory
By 1900, the fact of evolution was established,
but the genetic basis of evolution was not yet
understood.
Then the work of Gregor Mendel was
rediscovered, and during the 20th century,
work continued on the genetic basis of
evolution.
A “modern synthesis” of genetics and
evolution took place 1936–1947.
Evolution Is Both Factual and the Basis of Broader Theory
The structure of DNA was established by
1953 by Watson and Crick.
In the 1970s, technology developed for
sequencing long stretches of DNA and
amino acid sequences in proteins.
Evolutionary biologists now study gene
structure and evolutionary change using
molecular techniques.
Evolution of Staph
Natural selection does not create new
traits, but edits or selects for traits
already present in the population
The local environment determines which
traits will be selected for or selected
against in any specific population
Evidence supporting evolution
Fossil record
• transition species
Anatomical and Molecular Homology
• anatomy
• embryology & development
• molecular (DNA & protein)
• Vestigial
Biogeography
Artificial selection
• human-caused evolution
Fossil record
Layers of sedimentary rock contain fossils
• new layers cover older ones, creating a record over time
• fossils within layers show that a succession of organisms have populated Earth throughout a long period of time
Tiktaalik
• “missing link” from sea to land animals
What are Homologous structures?
Similar structure
Similar development
Different functions
Evidence of close evolutionary
relationship
• recent common ancestor
Anatomical record
Homologous structures
• similarities in characteristics resulting from
common ancestry
spines
tendrils
succulent leaves
colored leaves
Homologous structures in plants!
leaves
needles
Analogous structures
Separate evolution of structures
similar functions
similar external form
different internal structure &
development
different origin
no evolutionary relationship
Solving a similar problem with a similar solution
Don’t be fooledby their looks!
Analogous Structures are evidence for Convergent evolution
Flight evolved in 3 separate animal groups
• evolved similar “solution” to similar “problems”
• analogous structures
Does this mean they have a recent common ancestor?
Convergent evolution
Fish: aquatic vertebrates
Dolphins: aquatic mammals
similar adaptations to
life in the sea
not closely related
Those fins & tails & sleek bodies areanalogous structures!
Parallel Evolution
• filling similar ecological roles in similar environments, so similar adaptations were selected
• but are not closely related
marsupial
mammalsplacental
mammals
Comparative embryology
Similar embryological development in closely related
species
• all vertebrate embryos have similar structures at
different stages of development
gill pouch in fish, frog, snake, birds, human,
etc.
Which one is the salamander, human, fish, cow, pig, rabbit,
turtle, and chicken?
Molecular record
0 25 50 75 100 1250
25
50
75
100
Millions of years ago
Horse/donkey
Sheep/goat
Goat/cow
Llama/cow
Pig/cow
Rabbit/rodent
Horse/cow
Human/rodent
Dog/cow
Human/cow
Human/kangaroo
Nu
cle
oti
de s
ub
sti
tuti
on
s
Comparing DNA & protein structure
• universal genetic code!
DNA & RNA
• compare common genes
cytochrome C (respiration)
hemoglobin (gas exchange)
Closely related species have
sequences that are more similar
than distantly related species
DNA & proteins are a molecular
record of evolutionary relationships
Why comparethese genes?
Comparative hemoglobin structure
Number of amino acid differences betweenhemoglobin (146 aa) of vertebrate species and that of humans
100 20 30 40 50 60 70 80 90 100 110 120
LampreyFrogBirdDogMacaqueHuman
328 45 67 125
Why does comparingamino acid sequencemeasure evolutionaryrelationships?
Vestigial organs
Modern animals may have structures that serve little or no function
• remnants of structures that were functional in ancestral species
• deleterious mutations accumulate in genes for non-critical structures without reducing fitness
snakes & whales — remains of pelvis & leg bones of
walking ancestors
eyes on blind cave fish
human tail bone
This is notLaMarck’s loss from “disuse”!
Vestigial organs
Hind leg bones on whale fossils
Why would whaleshave pelvis & leg bonesif they were alwayssea creatures?
Biogeography
Biogeography- the geographic distribution of
species
Earth’s continents were formerly united in a single
large continent called Pangaea, but have since
separated by continental drift
An understanding of continent movement and
modern distribution of species allows us to predict
when and where different groups evolved
Artificial selection
Artificial breeding can use variations in
populations to create vastly different “breeds”
& “varieties”
“descendants” of the wolf
“descendants” of wild mustard
Speciation and the
Origin of Life
How and why do new species originate?
Species are created by a series of evolutionary processes
• populations become isolated
geographically isolated
reproductively isolated
• isolated populations evolve independently
Isolation
• allopatric
geographic separation
• sympatric
still live in same area
Obstacle to mating or to fertilization if mating occurs
PRE-reproduction barriers
behavioral isolation
geographic isolation ecological isolation temporal isolation
mechanical isolation gametic isolation
Geographic isolation
Species occur in different areas
• physical barrier
• allopatric speciation
“other country”
Harris’s antelope
squirrel inhabits
the canyon’s
south rim (L). Just
a few miles away
on the north rim
(R) lives the
closely related
white-tailed
antelope squirrel
Ammospermophilus spp
Ecological isolation
Species occur in same region, but occupy different
habitats so rarely encounter each other
• reproductively isolated
2 species of garter snake, Thamnophis,
occur in same area, but one lives in water &
other is terrestrial
lions & tigers could
hybridize, but they
live in different
habitats:
lions in grasslands
tigers in rainforest
Temporal isolation
Species that breed during different times of day, different seasons, or different years cannot mix gametes
• reproductive isolation
• sympatric speciation “same country”
Eastern spotted skunk
(L) & western spotted
skunk (R) overlap in
range but eastern mates
in late winter & western
mates in late summer
Behavioral isolation
Unique behavioral patterns & rituals isolate species
• identifies members of species
• attract mates of same species • courtship rituals, mating calls
reproductive isolation
Blue footed boobies mate
only after a courtship display
unique to their species
sympatric speciation?
Mechanical isolation
Morphological differences can prevent successful mating
• reproductive isolation
Even in closely related
species of plants, the
flowers often have distinct
appearances that attract
different pollinators.
These 2 species of monkey
flower differ greatly in
shape & color, therefore
cross-pollination does not
happen.
Plants
sympatric speciation?
Mechanical isolation
For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer• lack of “fit” between sexual organs:
hard to imagine for us… but a big issue for insects with
different shaped genitals!
Damsel fly penises
Animals
I can’t even imagine!
Gametic isolation
Sperm of one species may not be able to fertilize eggs
of another species
• mechanisms
biochemical barrier so sperm cannot penetrate egg
o receptor recognition: lock & key between egg & sperm
chemical incompatibility
o sperm cannot survive in female reproductive tract
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
sympatric speciation?
POST-reproduction barriers
Prevent hybrid offspring from developing into a
viable, fertile adult
• reduced hybrid viability
• reduced hybrid fertility
• hybrid breakdown
Liger:Mom was
tiger
Tigon: Mom was lion
http://www.lairweb.org.nz/tiger/tigons.html
Reduced hybrid viability
Genes of different parent species may interact &
impair the hybrid’s development
Species of salamander
genus, Ensatina, may
interbreed, but most
hybrids do not complete
development & those
that do are frail.
sympatric speciation?
Mules are vigorous,
but sterile
Reduced hybrid fertility
Even if hybrids are vigorous they may be sterile
• chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes
Donkeys have 62
chromosomes
(31 pairs)
Horses have 64
chromosomes
(32 pairs) Mules have 63 chromosomes!
Hybrid breakdown
Hybrids may be fertile & viable in first generation,
but when they mate offspring are feeble or sterile
In strains of cultivated rice,
hybrids are vigorous but
plants in next generation are
small & sterile.
On path to separate species.
sympatric speciation?
Gradualism
Gradual divergence over
long spans of time
• assume that big
changes occur as the
accumulation of
many small ones
Punctuated Equilibrium
Rate of speciation is not
constant
• rapid bursts of change
• long periods of little or
no change
• species undergo rapid
change when they 1st
bud from parent
population
Time
Bacteria Archae-bacteria
AnimaliaFungiProtista Plantae
4500
4000
3500
3000
2500
2000
500
1500
0
1000
Formation of earth
Molten-hot surface ofearth becomes cooler
Oldest definite fossilsof prokaryotes
Appearance of oxygenin atmosphere
Oldest definite fossilsof eukaryotes
First multicellularorganisms
Appearance of animalsand land plants
Colonization of landby animalsPaleozoic
Mesozoic
Cenozoic
Millio
ns
of
ye
ars
ag
o
AR
CH
EA
N PR
EC
AM
BR
IAN
PR
OT
ER
OZ
OIC
The evolutionary tree of life can be documented with evidence.
The Origin of Life on Earth is another story…
What is Life?
First we have to define LIFE…
• organized as cells
• respond to stimuli
• regulate internal processes homeostasis
• use energy to grow metabolism
• develop change & mature
within lifetime
• reproduce heredity
o DNA / RNA
adaptation & evolution
Conditions on early Earth
Reducing atmosphere
• water vapor (H2O), CO2, N2, NOx, H2, NH3,
CH4, H2S
• lots of available H & its electron
• no free oxygen
Energy source
• lightning, UV radiation,
volcanic
low O2 =
organic molecules
do not breakdown
as quickly
What’s missingfrom thatatmosphere?
Water vapor
Condensed liquid with complex, organicmolecules
Condenser
Mixture of gases("primitiveatmosphere")
Heated water("ocean")
Electrodes discharge sparks(lightning simulation)
Water
Origin of Organic Molecules: Organic Soup Model
Abiotic synthesis
• 1920Oparin & Haldanepropose reducing atmosphere hypothesis
• 1953Miller & Ureytest hypothesis
formed organic compounds
o amino acids
o adenine
CH4
NH3
H2
Origin of Genetics
RNA is likely first genetic material
• multi-functional
• codes information
self-replicating molecule
makes inheritance possible
natural selection & evolution
• enzyme functions
ribozymes
replication
• regulatory molecule
• transport molecule
tRNA & mRNA
Dawn of natural selection
Prokaryotes
Prokaryotes dominated life
on Earth from 3.5–2.0 bya
3.5 billion year old
fossil of bacteria modern bacteria
chains of one-celledcyanobacteria
Stromatolites
Fossilized mats of prokaryotes resemble modern microbial colonies
Lynn Margulis
Oxygen atmosphere
Oxygen begins to accumulate 2.7 bya
• reducing oxidizing atmosphere
evidence in banded iron in rocks = rusting
makes aerobic respiration possible
• photosynthetic bacteria (blue-green algae)
First Eukaryotes
Development of internal membranes• create internal micro-environments
• advantage: specialization = increase efficiency natural selection!
infolding of theplasma membrane
DNA
cell wall
plasmamembrane
Prokaryoticcell
Prokaryotic ancestor of eukaryotic cells
Eukaryoticcell
endoplasmicreticulum (ER)
nuclear envelope
nucleus
plasma membrane
~2 bya
Endosymbiosis
Ancestral eukaryotic cell
Eukaryotic cellwith mitochondrion
internal membrane
systemaerobic bacterium mitochondrion
Endosymbiosis
Evolution of eukaryotes• origin of mitochondria
• engulfed aerobic bacteria, but did not digest them
• mutually beneficial relationship
natural selection!
mitochondrion
chloroplast
Eukaryotic cell with
chloroplast & mitochondrion
Endosymbiosis
photosynthetic
bacterium
Endosymbiosis
Evolution of eukaryotes• origin of chloroplasts
• engulfed photosynthetic bacteria, but did not digest them
• mutually beneficial relationship natural selection!
Eukaryoticcell with mitochondrion
Evidence
• structural
mitochondria & chloroplasts resemble bacterial structure
• genetic
mitochondria & chloroplasts have their own circular DNA, like bacteria
• functional
mitochondria & chloroplasts move freely within the cell
mitochondria & chloroplasts reproduce independently from the cell
Theory of Endosymbiosis
Lynn Margulis