Module 1: Evolution
Month Day TopicAug 28 History of life on Earth
30 Theory of evolution
Sept 1 Timeline construction
4 Holiday
6 Evidence for evolution
8 Mechanisms of evolution I
11 Mechanisms of evolution II
13 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
• 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 (boneswhere manyother mammalshave a tail)
small boneattached topelvic girdle
thighboneattached topelvic 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)
• Collected and examined the species that inhabited the regions the ship visited
• Started 5 year, round-the-world voyage aboard the Beagle at age 22
The voyage of H.M.S. Beagle
Pleistocene glyptodont
Modern armadillo
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