Transcript Slide 1

EVOLUTION
Dr. Aslı Tolun
Dept. Mol. Biol. and Genetics
April-May 2010
Science 102
EVOLUTION
 The most important theory in
biology: The unifying theory.
 Not a hypothesis.
 Theory: NOT a speculation!!
A statement of well-supported
general laws, principles and causes
of something known or observed.
 T. Dobzhansky in 1973:
“Nothing in biology makes sense,
except in the light of evolution.”
CONCEPTS in SCIENCE
 Fact: An observation that has been
repeatedly confirmed.
 Law: A descriptive generalization about
how some aspects of the natural world
behave under stated circumstances.
 Hypothesis: A testable statement about the
natural world that can be used to build
more complex inferences and explanations.
 Theory: A well-substantiated explanation of
some aspects of the natural world that can
incorporate facts, laws, inferences and
tested hypotheses.
IN SCIENTIFIC RESEARCH
You can:
 Perform experiments.
 Observe.
Science: testable! No dogma.
EVOLUTION
Individuals in a population have
differences.
The differences are heritable.
Natural selection and elimination.
Leads to speciation.
A common ancestor for all species.
EVOLUTION is a FACT
There is no (scientific) evidence
against it.
All scientists accept evolution.
No “believing in” evolution, but
“accepting evolution as a fact”.
CONSEQUENCES
 The fittest survives
 Selection works on it
 Evolution.
 Final outcome:
Usually not perfect!
Vertebral column is not well adapted
to vertical posture.
A: A better arrangement in squid eye: axons arise from rear of
retinal cells, so eye is more efficient plus there is no blind spot.
B: Vertebrate eye with blind spot: nerve cell extentions arise
from front of retinal cells to form optic nerve.
FINAL CONSEQUENCE:
SPECIATION
•All known species are descended from
common ancestors.
•Their relationships can be described as a
branching tree (phylogeny) in which each fork
represents divergence from a common
ancestor into two different lineages.
•Each lineage evolves various differences from
other lineages and eventually leads to a new
species.
•Similarities between lineages are due to
inheritance.
THE THREE DOMAINS:
MECHANISMS OF
SPECIATION
•Geographic isolation.
•Seasonal isolation.
•Ethological isolation
(behavioral incompatibilities).
•Mechanical isolation.
•Genetic changes leading to
hybrid sterility.
EXAMPLE for SPECIES RELATIONS:
DIVERGENCE vs
CONVERGENCE
D: Features diverge but retain the
basic structures.
Human arm vs horse leg.
C: Distantly related species can
evolve features that serve the
same function and are seemingly
similar.
Bat wing vs insect wing.
Change in form with similar function
IS EVOLUTION POSSIBLE?
Yes, if sufficient time passes...
IMPORTANCE of SCIENCE
SCIENTIFIC THOUGHT IS BENEFICIAL
 Understanding humans: genes,
development, function
 Applications for human health
 Understanding the evolution of microbes
 Applications in agriculture, pest control
 Biotechnology
 Utilizing natural resources (GAP)
 Leading a rational life.
WHY IS THERE OPPOSITION?
In the 17th and 18th centuries, science was
not developed.
Bible: Earth was created in 4004 BC.
All life forms were created as they are today,
perfectly adapted to each other and to
environment.
Creation story is important for Christianity.
But last year.....
CONTRIBUTORS to MODERN SCIENCE
 Copernicus 1473-1543
 Galileo 1564-1642
 Newton 1642-1727
 Lamarck: directional change
 In 1860s: biologists and geologists
accepted evolution as a fact.
 Mechanism? Purpose?
CHARLES DARWIN
1809 – 1882. A naturalist.
His father was a physician
Grandfather Erasmus Darwin a physicist
Education: Two years in medicine,
later for a ministry.
1839 married his cousin, 10 children, – 2.
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HMS BEAGLE
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A navy survey ship
South America in Dec 1831, 5 years.
Collected specimens: fossils and living
Driving force: curiosity
Observation capacity
Hard work.
HIS MOST IMPORTANT BOOKS
Total of 25 books. Best known are:
1839 Excursions in Beagle, 3 volumes "Journal of
Researches into the Natural History and Geology of the
Countries Visited During the Voyage of H.M.S. Beagle”.
Authors: Kaptan Philip King, Kaptan Robert FitzRoy ve
Charles Darwin.
1859 "The Origin of Species by Means of Natural Selection:
Or, the Preservation of Favored Races in the Struggle
for Life”.
1871 "The Descent of Man and Selection in Relation to
Sex”.
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Charles Darwin
The Origin of Species
As more individuals are produced than can possibly survive …
Can it be thought improbable, seeing that variations useful to
man have undoubtedly occurred, that other variations useful
in some way to each being in the great and complex battle of
life, should sometimes occur in the course of thousands of
generations? If such do occur, can we doubt that individuals
having any advantage, however slight, over others, would
have the best chance of surviving and of procreating their
kind? On the other hand, we may feel sure that any variation
in the least degree injurious would be rigidly destroyed. This
preservation of favorable variations and the rejection of
injurious variations, I call Natural Selection.
INSPIRED by THOMAS MALTHUS
Thomas Malthus (1766-1834) in 1798:
“Food is necessary to the existence of man.
Secondly, that the passion between the sexes is
necessary, and will remain nearly in its present
state”.
Populations tend to increase faster than the increase
in resources.
“This implies a strong and constantly operating
check on populations from the difficulty of
subsistence.”
DARWIN’S HYPOTHESES ON COMMON ANCESTRY
1. Single origin of known life (or few origins)
2. Repeated branching of lineages (speciation)
3. Each lineage may acquire more differences
over time, hence
4. Lineages gradually diverge (become more
different), so
5. Very similar species are likely to have a recent
common ancestor; more different species are
likely to have a less recent (more remote)
common ancestor.
Phylogenies form the basis for
Hypotheses and Predictions
In each great region of the world the living
mammals are closely related to the extinct
species of the same region.
It is therefore probable that Africa was formerly
inhabited by extinct apes closely allied to the gorilla
and chimpanzee; and as these two species are now
man’s nearest allies, it is somewhat more probable
that our early progenitors lived on the African
continent than elsewhere.
Charles Darwin, 1871, The Descent of Man
DO WE COME FROM MONKEYS?? 
GALAPAGOS ISLANDS
• Similar land
• Similar geography
• Different species.
WHY IS EVOLUTION
DARWIN’S?
His work was scientific, intensive and
explained evolution best.
1859: On the Origin of Species
Evolution was accepted within a few
years.
IMPACT OF EVOLUTION
• Understanding biology, thus the world.
• Establishment of scientific thought
• Secularization of science and education.
EVIDENCE for EVOLUTION
SUPPORTING SCIENCES
• Fossils – extinct species, ancestral
species
• Geology – the age of earth
• Voyages
• Classifications: Carl von Linné
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EVIDENCE for EVOLUTION
A. Homologous characters. A feature in two
or more species is homologous when it is
derived from the same feature of their
nearest common ancestor.
Wings of bats vs of flies
HOMOLOGY
EVIDENCE for EVOLUTION
B. Reapitulation – appearance and
subsequent loss of structures in ontology,
which in related taxa are attained in the
adults.
Embryos of the baleen whales develop teeth
that are observed later.
Embryos of birds and mammals develop gill
slits.
EVIDENCE for EVOLUTION
C. Vestigial structures. Eyes in cave
animals, human appendix, leg bones in
snakes etc.
→ Common descent, variation, selection.
D. Embryology – embryos of all vertebrates
are similar.
Vestigial eye of cave fish, Astyanax mexicanus
Figure 2 Surface dwelling (eyed) and cave-dwelling (eyeless) forms of Astyanax mexicanus. Adjacent to them are sections of
the embryonic eyes, stained with a reagent (TUNEL) that binds to and stains DNA fragments produced by apoptosis. A1.
Surface form with eyes and pigmentation. A2. 25 hour embryo of surface form, showing very little apoptosis in the lens. B1.
Cavefish from La Cueva Chica with reduced eyes and reduced pigmentation. B2. 25 hour embryo of the Chica cave-dwelling
form, showing severe apoptosis in the lens vesicle (arrowhead). C1. Cavefish from Cueva de El Pachón showing neither eye nor
pigmentation. C2. Apoptosis in lens and corneal epithelium in the 25 hour embryo of the Cueva de El Pachón cavefish. (After
Jeffery and Martasian, 1998.)
Apoptosis =
Programmed
cell death
EVIDENCE for EVOLUTION
E. Biogeography.
Similarities in fauna and flora in parallel with
geological history.
Dispersal.
Many oceanic islands lack organisms such as mammals and snakes
that thrive there after being introduced by humans.
Why weren’t there any mammals or snakes before introduction?
Placentals vs marsupials
Mongoose
Brown tree snake
EVIDENCE for EVOLUTION
F. Molecular evidence: a single ancestral
cell and similarity in genomes.
G. Imperfections.
H. Fossils.
Archaeopteryx (B),
intermediate between
dinosaurs and birds,
found in 19th century.
Recently, many other
intermediates, such
as Microraptor
(top).
Birds descended from
dinosaurs; they ARE
feathered dinosaurs!
Stages in evolution from lobe-finned fishes to tetrapods
Note similarities and changes in skull
Tiktaalik
EVIDENCE for EVOLUTION
I. Artificial selection.
J. Similarities in similar features.
Stages of eye complexity in mollusks
(limpet Patella)
(slit shell mollusk Pleurotomaria)
HUMAN EVOLUTION
CHARACTERISTICS of APES
and HUMANS
• Posture: Bent over or quadrupedal,
“knuckle-walking” common / upright,
bipedal
• Leg and arm length: arms longer than
legs, arms adapted for swinging
• Feet: Opposable big toes, capable of
grasping / adapted for walking
• Teeth: prominent / reduced
• Skull: bent forward from spinal column /
held upright
CHARACTERISTICS of APES
and HUMANS
• Face: sloping, jaws jut out, wide nasal
opening / chin
• Brain size: 280 to 705 cm3 / 400 to 2000
cm3 (fossil to present)
• Amount of hair cover
• Spine straight / S-shaped
• No language / language
HUMAN EVOLUTION
kafalar
HUMAN EVOLUTION
About 40 000 years ago, at least 4 species
of Homo
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Sapiens
Neanderthals
Flores people
Altai.
WE KNOW THE GENES FOR
Brain expansion
Speech
Most relationships among primates that had been proposed, based on
morphological data, have been supported by DNA sequences.
The DNA sequences do not reflect adaptation of morphologically similar species to
similar environments, because the same result is obtained from nonfunctional
DNA sequences, such as the hemoglobin pseudogene.
Australopithecus afarensis, ca. 3.5 million years
Tanzania
DO NEW MUTATIONS OCCUR?
• Duchenne type muscular
dystrophy:
– 1 in 3500 boys
– 1/3 are new mutations
• Hemophilia, achondraplasia
etc.
• Most are eliminated.
29 Eylül 2009
Kocaeli Üniversitesi
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29 Eylül 2009
Kocaeli Üniversitesi
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NOT ALL MUTATIONS ARE
ELIMINATED
ELIMINATION DOES NOT WORK ON:
• Huntington disease
• Osteoporosis
• Most heart diseases
Why?
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AN EXAMPLE
SICKLE CELL ANEMIA and THALLASEMIA
• Heterozygotes are resistant to malaria
SELECTION!
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Red blood cells with normal hemoglobin and with sickle-cell hemoglobin
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OTHER RESISTANCES
• Several genetic diseases
Also, infectious diseases:
• Tuberclosis, lepra, AIDS etc.
Even to parasites, such as worms.
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GENETIC SUSCEPTIBILITY
• Diseases: heart disease, cancer etc.
• Obesity
• Alcoholism
• Suicide
• Aggression
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ACKNOWLEDGMENT
 Douglas J. Futuyma, State University of New
York. Boğaziçi University lecture in 2007.
 Francisco J. Ayala, University of
California xx. Boğaziçi University lecture in
2009.