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Transcript
ANTH/BIOL/GEOL/HIST/ PHIL 225
Class 13, Feb 22
Natural selection and adaptation
Prof. Beall for Prof. Princehouse
Dr. Princehouse will hold extra office hours
Wednesday 3-4 pm.
Materials you have read or seen:
•Futuyama on natural selection and adaptation
•Video on natural selection
•Video on sexual selection
•Spandrels article (?Spaniels article)
Materials you have brought to class:
3 written questions on the readings
EVOLUTION
• The process of biological change through time.
• The mechanism is natural selection.
• The outcome is organisms adapted to their
environments.
Evolution by natural selection has three essential
elements.
Organisms have reproductive
capacity that is rarely fulfilled
because environmental resources
are limited.
Organisms vary in their
ability to survive and
reproduce.
Variation is heritable.
EVOLUTION BY NATURAL
SELECTION: 3 postulates
1. Species are capable of
producing offspring faster than
their resources can support
Some estimate there were 3-5 billion passenger
pigeons in North America when Europeans first
arrived.
The last one died in 1914.
Old magazine illustration of
hunters shooting Passenger
Pigeons. Note the density of the
flight. During migration, flocks
could be 1 mile wide and
300 miles long, taking several
hours to pass.
http://www.stanford.edu/group/stanfordbirds/text/essays/essaypix/Passenger_Pigeon.gif
https://www.geology.ucdavis.edu/iype/sept/passengerpigeon.jpg
EVOLUTION BY NATURAL
SELECTION: 3 postulates
2. Variation among organisms
affects their ability to survive and
reproduce in their environment
“Any minute variation in structure, habits or
instincts adapting that individual to the new
conditions would tell upon its vigour and
health” (C. Darwin, 1858, p. )
http://www.pbs.org/safarchive/images/img_5cool/galapagos/finches.gif
http://home.comcast.net/~mkent595/Micro10.JPEG
http://www.anth.ucsb.edu/faculty/walker/classes/anth105/index_files/image002.jpg
Variation is abundant.
http://www.newscientist.com/data/images/ns/cms/mg20427342.500/mg20427342.500-1_300.jpghttp://images.mirror.co.uk/upl/m4/aug2009/6/1/baboon-2957207.jpg
http://learn.genetics.utah.edu/content/begin/traits/images/hand_clasp.jpg
EVOLUTION BY NATURAL
SELECTION: 3 postulates
3. Variations are heritable
Variations are heritable.
Hitch-hiker’s thumb is a recessive
trait.
Non-roller is a recessive trait.
Height is influenced by
heredity and environment.
http://www.newscientist.com/data/images/ns/cms/mg20427342.500/mg20427342.500-1_300.jpghttp://images.mirror.co.uk/upl/m4/aug2009/6/1/baboon-2957207.jpg
http://learn.genetics.utah.edu/content/begin/traits/images/hand_clasp.jpg
Galapagos finch species depicted here have all
arisen from a common ancestor, but have evolved
a remarkable diversity of beak shapes and sizes
as they have adapted to exploit different food
sources
Depth and breadth
of beaks
controlled by
calmodulin locus.
Length of beaks
controlled by
BMP4 locus.
The outcome of evolution by natural selection
• Species are well adapted to their
environment
• Tremendous variety of species
• Tremendous variety of organisms
Well adapted organisms are the outcome of
evolution by natural selection
• Organisms with variants that make them
better able to survive contribute
disproportionately to the next generation
• Over time, what happens?
– Descendent organisms have different
features, structures, behaviors than their
ancestors.
– Environmental inevitably changes.
Adaptations are the features that improve
survival.
• Adaptations work.
• Adaptations are not perfect.
• The process is called natural selection, not natural
perfection.
• New features of organisms result from natural selection
The Antarctic ice fish has several new features.
It is related to the mackerel.
Mackerel is like the
ancestor fish.
http://www.glaucus.org.uk/Mackerel.jpg
Ice fish is descended from its
ancestor with more modifications.
http://www.underwatertimes.com/news.php?article_id=632194710
The ice fish have adapted to low ambient
temperature and have low body temperature.
• Icefish are pale because they do not make
hemoglobin and don’t have red blood
cells. They have ‘ice water’ in their veins.
• Icefish are pale because they don’t make
myoglobin.
The Antarctic ice fish has no red blood cells,
no hemoglobin, and no myoglobin.
•
•
•
•
How can they survive?
They adsorb oxygen from the water.
How did this come about?
Water temperature dropped from about 68
ºF to < º30 F in the past 55 million years.
The genetic fossil record reveals the changes that
caused the loss of hemoglobin and myglobin.
• One hemoglobin gene is nonfunctional and one is
just gone.
• Myoglobin gene is non-functional.
• We can see the remnants of these genes. They have
‘gone extinct’.
Genetic changes resulted in the addition of
antifreeze proteins in veins.
• Antifreeze proteins are necessary to prevent freezing
solid.
• These antifreeze genes arose from a part of a gene
that originally encoded a digestive enzyme.
• Part of that enzyme broke off and relocated to
another place in the fish genome, replicated, and
now makes antifreeze.
Icefish adaptations are examples of chance,
necessity and tinkering.
•
•
•
•
Improvised series of steps.
Destruction of some old genetic code
Tinkering with some code to make new genetic code.
Icefish evolved from a warm-water, hemoglobindependent lifestyle to a very-cold-water, oxygen
adsorbing, antifreeze-making lifestyle.
Coat color of rock pocket mouse is another
example of descent with modification that has
occurred in many species.
MC1R gene has two
alleles. Two copies of
light allele results in
sandy color of mice.
MC1R allele in humans and our
ancestors accounts for blonde and
red hair in modern humans and our
ancestors including Neanderthals.
Galapagos finch species depicted here have all
arisen from a common ancestor, but have evolved
a remarkable diversity of beak shapes and sizes
as they have adapted to exploit different food
sources
Depth and breadth
of beaks
controlled by
calmodulin locus.
Length of beaks
controlled by
BMP4 locus.
High-altitude natives are a natural experiment of
adaptation to an extreme, lifelong stress: hypoxia.
100
%Sea Level PiO2
140
90
80
120
70
100
60
Inspired O2 , mmHg
80
50
60
40
0
1000
2000
3000
4000
Altitude, m
5000
6000
7000
% Sea Level PiO2
Inspired O2, mmHg
160
•Hypoxia is severe and
unavoidable.
•All residents at a given
altitude are exposed to
the same ambient
stress.
•All steps in the process
of oxygen delivery are
affected.
The Tibet Plateau has an average altitude of
15,000’ and is about 1500 x 600 miles in
extent and is extremely stressful.
Qinghai
Ladakh
Qinghai-Tibet Plateau
Phala
Lhasa
Shigatse
India
Nepal
NASA image
Phala’s is at 15,200-17,500’ altitude; Shigatse is at 13,000’.
Hemoglobin carries less oxygen at high
altitudes.
•
Altitude
% Oxygen saturation
Cleveland
98%
Pike’s Peak
80%
.
Tibetans have genotypes for high
or low oxygen saturation of
hemoglobin.
AA
SAT=80
++ 1%
BB
SAT=90
AB
SAT=89
AB
SAT=89
Altitude, Tibetans
% Oxygen Saturation
4200m BB genotype
88%
4200m AA genotype
78%
AA
SAT=80
http://www.pennhealth.com/health_info/images/19443.jpg
Women estimated to have genotypes for high
oxygen saturation have more living children.
Estimated
Genotype
Genotypic Means
# Pregnancies/
livebirths
# Living Children # Infant Deaths
Low O2 Sat (AA)
4.6/4.5
1.6
1.7
High O2 Sat (AB)
4.9/4.8
3.6
0.6
High O2 Sat (BB)
4.8/4.6
3.8
0.3
The outcome of evolution by natural selection
is organisms adapted to their environments.
An adaptation is a characteristic that
increases an organism’s chance of survival
and reproduction.
How do we identify adaptations?
St. Mark’s Cathedral, Venice
The Spandrels of San Marco
and the Panglossian Paradigm:
A Critique of the Adaptationist
Programme
STEPHEN JAY GOULD AND RICHARD C. LEWONTIN
http://www.aaas.org/spp/dser/evolution/history/spandrel
Spandrels of San Marco, Venice
http://www.jssgallery.org/Essay/Venice/San_Marco/Basilica_San_Marco/Basilica_San_Marco_interior.htm
Adaptationist Program, I
• Why does this trait exist?
• What is the function of a given structure or
organ?
• How has this trait contributed to
reproductive success?
• What is the evolutionary history of the
feature?
• Is the trait part of some other adaptive
machinery?
Adaptationist Program, II
• Develop a functional hypothesis
• Develop a test or tests of that hypothesis
• Predict other, unknown, aspects of human
biology and test those hypotheses, too
There are potential pitfalls.
• It is necessary to demonstrate the
operation of natural selection rather than
to assume it.
• Current function may not explain why a
trait evolved.
• If we start with the wrong trait, we get the
wrong explanation.
http://australianmuseum.net.au/Uploads/Images/9667/DSC_0027_big.jpg
The Spaniels of St. Marx and the
Panglossian Paradox: A Critique of
a Rhetorical Program
http://www.honeybet.co.uk/photos/doggroupweb.jpg