Download Historical Overview of Evolutionary Biology

Gene’s Eye View of Evolution
(Richard Dawkins, Oxford University):
The gene as the fundamental unit of
selection:
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The evolutionary importance of the
individual has been highly overrated
Individuals are ephemeral, mere blips
on the evolutionary landscape; DNA
is potentially immortal
We are survival machines - robot
vehicles blindly programmed to
preserve the selfish molecules known
as our genes.
Organisms are simply VEHICLES for
the transmission of REPLICATORS.
A Replicator has the property of
being able to make copies of itself.
Types of Replicators
• Passive Replicator - a replicator that has no
influence over its probability of being copied
• Active Replicator - a replicator whose
nature has some influence over its probability
of being copied
MAKES POSSIBLE ORGANIC EVOLUTION
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Properties of Successful Replicators
• Stability: the universe is populated by
stable entities (= Longevity)
• Speed of Replication: (= Fecundity)
• Accuracy of Replication (= Fidelity)
Kinds of Replicators
• Dead-end Replicators: not transmitted to the
next generation, e.g., somatic cells in metazoans
• Germ-line Replicators: theoretically immortal;
alleles
• ON EARTH, THE REPLICATOR IS
DNA
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Mutation: Mistakes in
Replication
• No replicator is capable of making perfect
copies of itself
• Mistakes in the replication process allow
for evolution in the face of environmental
change
Replicators: Airy-fairy or Fact?
HIV: An Active Replicator
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“Life Cycle” of HIV
Replicator/Vehicle Relations
Benign or malevolent?
• Importance of transmission mode
—Vertical vs. horizontal
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Science & Religion Defined
• Science: systematized knowledge derived from
observation, study, and experimentation carried out in
order to determine the nature or principles of what is
being studied.
• Religion: the belief in a divine or superhuman power
or powers to be obeyed and worshipped as the
creator(s) and ruler(s) of the universe.
What Distinguishes Science from Religion?
• Scientific theories are falsifiable (capable of being
able to be shown untrue or misleading). To be
considered scientific, a theory, in principle, must
be constructed in such a way that it is capable of
being disproved.
• Religion is based on faith.
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Scientific Method
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Observation
Question
Hypothesis ---> Predictions
Test of Predictions
—Strong inference: randomized, manipulative
experiment
—Weak inference: correlational analysis gives a result
consistent with the hypothesis
• If predictions independently validated --> Theory
What is Theory?
• Theory: a scheme or system of ideas and statements held
as an explanation or account of a group of facts or
phenomena; a hypothesis that has been confirmed or
established by observation or experiment, and is
propounded or accepted as accounting for the known facts.
• Because theory is a set of statements, it usually does not
stand or fall on the basis of a single critical test, as simple
hypotheses do. Rather, theories evolve as they are
confronted with new phenomena or observation; parts of
the theory are discarded, modified or added.
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Historical Overview of Evolutionary
Thought
• Ancient Greeks (Plato & Aristotle): Typological View of
Nature - individual variation as the imperfect manifestation of
ethos. Ideas are an eternal, unchanging essence (Ethos are
eternal ideas that exist in the mind of God)
• Christian Theology: Scala Naturae or the Great Chain of
Being. The ladder of life consists of gradation from inanimate
material through plants, through lower animals and humans to
angels and other spiritual beings.
• Natural Theology: adaptations of organisms as evidence for
the Creator’s benevolence; e.g., John Ray’s (1701) “The
Wisdom of God Manifested in the Works of the Creation”
First articulated theory of evolution
Jean-Baptiste Lamarck, 1809
Philosophie Zoologique
• Organisms continually arise by
spontaneous generation
• Organisms develop adaptations
to a changing environment
through the use and disuse of
organs
• Acquired characteristics are
inherited
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Lamarck vs. Darwin
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What good, Lamarck?
• If nothing else, demonstrates that theory in
evolutionary biology can be falsified-Lamarck’s ideas were resoundingly rejected!
—The notion of continual spontaneous generation
was challenged by geologists and the principle of
uniformitarionism, i.e., the same processes are
responsible for shaping past and current events
—Many empirical studies have demonstrated, that,
in effect, you cannot inherit a good sun tan
ON THE ORIGIN OF SPECIES BY NATURAL
SELECTION 1859
• Competition
• Individual Variation
• Heritability
• Blending Inheritance
(hereditary factors
mix in the blood)
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Particulate Theory of
Inheritance
Evolution: Post-Darwin
• Darwin’s Theory of Evolution by Natural Selection suffered
from a lack of understanding of inheritance and the basis of
genetic variation; Darwin believed in blending inheritance.
• NeoDarwinism-The Modern Synthetic Theory of
Evolution-The Modern Synthesis
• Marriage of Darwin’s principle of natural selection with
Mendel’s discovery of particulate inheritance
• Hereditary information is encoded in genetic material
called genes
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Blending versus Particulate Inheritance:
Fate of a Favorable Mutation
Founders of the Modern Synthesis
Ronald A. Fisher: theoretical population
geneticist; founder of modern statistics
& experimental design
J.B.S. Haldane: theoretical population
geneticist; Haldane's rule of speciation
Sewall Wright: theoretical population
geneticist; believed that genetic drift
was an major force in evolution
Theodosius Dobzhansky: Drosophila
geneticist who integrated population
genetic theory with empirical data on
genetic variation
Julian Huxley: Ornithologist who used
genetic principles to explain
macroevolutionary patterns
Ernst Mayr: Systematist; perhaps best
known for the "biological species
concept"
George G. Simpson: Paleontologist who
used genetic principles to explain
macroevolutionary patterns
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The Modern Synthesis
• Genetic variation arises by chance due to imperfections in DNA
replication (mutation) and recombination (crossing over of
homologous chromosomes during meiosis)
• Populations evolve by changes in gene frequency brought about
by random genetic drift, gene flow and especially natural selection
• Most beneficial mutations cause slight changes in the phenotype
and therefore evolutionary change tends to be slow and gradual
• Speciation (new species formation) occurs gradually when
populations are reproductively isolated by geographic barriers
The Molecular Genetic Revolution
• The Double Helix
(Watson & Crick,1953)
• The Central Dogma
(DNA-->RNA-->Protein)
• Genetic engineering
• DNA fingerprinting
• Genome sequencing
Selfish genetic elements:
a pervasive feature of
organismal genomes
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