Transcript The theory of evolution

Module 1: Evolution
Month Day Topic
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Sept
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History of life on Earth
Theory of evolution
Timeline construction
Holiday
Evidence for evolution
Mechanisms of evolution I
Mechanisms of evolution II
Speciation
Outline
1. History
2. Cultural and scientific context of
Darwin’s theory of evolution
3. The theory
4. Modern ideas
Organic evolution
The descent of modern
organisms with modification
from preexisting life-forms
Time
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Cosmological
Geological
Evolutionary
Ecological
Physiological
Hierarchy of scientific
information
Theory
Fact
Model
Hypothesis
Hypothesis--a limited statement implying
cause and effect in certain situations.
Model--a hypothesis that has been shown
to have more general validity.
Fact–a highly corroborated hypothesis
that has been so repeatedly tested and
for which so much reliable evidence
exists, that it would be perverse or
irrational to deny it.
Theory or Law—unification of facts. A
unifying and self-consistent explanation
of fundamental natural processes or
phenomena that is totally constructed
from facts.
Cultural and scientific context
of the theory of evolution
Idea of fixed species
• Ancient Greeks (2500 years bp):
– species do not change
Idea of fixed species
• Ancient Greeks (2500 years bp):
– species do not change
• Judeo-Christian (2000 years bp):
– species do not change
– each species divinely created
– earth ~ 6000 years old
Confounding Evidence
• Biogeography
• Comparative anatomy
• Geologic discoveries
Confounding evidence:
Biogeography
• Size of the known world expanded in the
15th century
• Discovery of new organisms could not be
explained by accepted beliefs
– How did species get from center of creation
(e.g., garden of Eden) to all these places?
Confounding evidence: comparative
morphology
• Study of similarities and differences in
body plans of major groups
• Puzzling patterns:
– Animals as different as humans and dogs
have similar bones in forelimbs
– Some parts seem to have no function
backbone
pelvic girdle
coccyx (bones
where many
other mammals
have a tail)
thighbone
attached to
pelvic girdle
small bone
attached to
pelvic girdle
Geological Discoveries
• Similar rock layers throughout world
• Certain layers contain fossils
• Deeper layers contain simpler fossils than
shallow layers
• Some fossils seem to be related to known
species
1800s - New Theories
• Scientists attempt to reconcile evidence
of change with traditional belief in a
single creation event
•Two examples
–Georges Cuvier (1769-1832) - multiple
catastrophes
–Jean Lamarck (1744-1829) - inheritance of
acquired characteristics
The New Geology
• Hutton and Lyell (1830s):
– Uniformitarianism: the present is the key to
the past
–Gradualism: slow process over vast periods
of time can cause big changes
–Earth is seriously old!
Principles of populations
• Thomas Malthus (1766-1834):
– Exponential growth of populations
Principles of populations
• Thomas Malthus (1766-1834):
– Exponential growth of populations
– “Positive checks” on population growth
• War
• Disease
• Famine
– As populations increase, resources
dwindle, the struggle to live intensifies,
and conflict increases
Charles Darwin (1809-1882)
• Started 5 year, round-theworld voyage aboard the
Beagle at age 22
• Collected and examined the species
that inhabited the regions the ship
visited
The voyage of H.M.S. Beagle
Modern armadillo
Pleistocene glyptodont
Evolution:
Descent with modification
But what causes modification?
What is the mechanism?
Galapagos Finches
• Darwin observed a variety of lifestyles
and body forms
• On his return, he learned that there
were 13 species
• He attempted to correlate variations in
their traits with environmental
challenges
Darwin’s facts
• Any species is capable of increasing its
population exponentially
• BUT we rarely see this increase—populations
tend to stay within certain limits
• Conclusion: not all offspring produced survive
• Conclusion: there is a “struggle for existence”
going on in all species
Darwin’s facts
• Individuals in any species vary
• Some vary in ways that help them survive and
reproduce; others vary in ways that decrease
their chances of survival
• Variation is inherited (somehow)
• Conclusion: a species will change over time,
producing new and different varieties (evolution)
Darwin’s theory
– Fact #1: Overproduction and struggle for
existence
– Fact #2: Heritable individual variation
The inescapable conclusion:
Differential or unequal reproductive success
causes evolution. He called this natural
selection.
Artificial selection as an analog of
natural selection
Natural selection
• Charles Darwin (1830-1850s): Ruminated on
theory, but didn’t publish
• Alfred Wallace (1850s): Independently
developed a theory similar to Darwin’s
• Darwin and Wallace “co-published” the theory
in 1858
• Darwin published The Origin of Species in
1859
Evolution:
Descent with modification
Evolution:
Descent with modification
Natural selection:
Differential reproductive success
Evolution:
Descent with modification
Natural selection:
Differential reproductive success
Darwin’s theory
– Fact #1: Overproduction and struggle for
existence
– Fact #2: Heritable individual variation
(no clear mechanism yet)
The inescapable conclusion: Differential or
unequal reproductive success
Ever since Darwin...
Ever since Darwin...
• Mendel develops theory of heredity (1860s)
– Parents pass onto their offspring discrete,
heritable factors that are responsible for
inherited traits.
– Discrete, heritable factors = genes
– Genes act in predictable ways
Ever since Darwin...
• The “Modern Synthesis” (mid-1900s):
– Often called “Neo-Darwinism”
– Adding in population genetics
– Mathematical models of evolution
Ever since Darwin...
• The molecular era (mid 1900s-present)
– Discovery of DNA as the basis of heredity
– Adding in a molecular mechanism
– Detecting the relationships among species
Ever since Darwin...
• The era of genomics (1990s-present)
– Mapping of genomes
– Rapid sequencing of genes
– Creation of molecular phylogenies