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Processes of Evolution
Plato and Aristotle
427-347 BC
384-322 BC
• Aristotle was the first to classify
living animals. He observed
patterns suggesting
transmutation; new types could
arise from older species
• Western culture – life forms
unchanged (immutable) since
• Some accounts claim this was
questioned 2000 years ago,
even before Aristotle and Plato
Early Beliefs
– Chain of Beings- Life extended from
lowest forms to humans, spiritual beings
were highest.
– Single Creation- All species were links
created at the same time at one center of
Age of Exploration
Led to new discoveries
• 15th century world travel began
• New species of plants and animals were discovered
• Naturalists cataloguing them identified patterns in where
species lived and whether they seemed related
• Among first to ponder about ecology and evolution
Evidence against concept of
“immutable species”
• Biogeography
• Comparative morphology
• Geologic discoveries
• Study of patterns in geographic
distribution of species and communities
• Accepted beliefs did not explain discovery
of new organisms in previously unknown
Comparative Morphology
• Study of similarities and differences in
body plans of major groups
• Puzzling patterns:
– Animals as different as whales and bats
have similar bones in forelimbs
– Some parts seem to have no function
(vestigial structures)
Comparative Morphology
fossilized ankle bone
ankle bone
Comparative Morphology
Comparative pelvic anatomy
Geological Discoveries
• Similar rock layers throughout world
• Certain layers contain fossils
• Deeper layers contain simpler fossils than
shallow layers
• Some fossils resemble known species
19th Century: New Theories
• Scientists attempt to reconcile evidence
of change with traditional belief in a
single-creation event
• Thoeries
– Georges Cuvier: catastrophism
– James Hutton: gradualism
– Jean Lamarck: teleological evolution
(evolution with a predetermined purpose!)
Georges Cuvier (1769-1832)
French anatomist
• Fossil species from Paris Basin
• older strata had flora and fauna
increasingly dissimilar from
modern life
• extinction common occurrence 
new species appear,
others disappear
• theory of catastrophism –
following creation
global disasters destroyed
repopulated from other areas
James Hutton (Scottish Geologist)
Theory of Gradualism (1795)
• profound change 
cumulative product of
slow but continuous
Jean Baptiste Lamarck
Theory of Evolution
(Philosophie Zoologique,1809)
Organisms had a drive to
 evol. responds to “felt needs”
teleological - evolution has a
goal, or directed purpose
species changed over time
because they "wanted" to be
1st to combine evolutionary and
ecological thinking
Lamarck’s Theories
Proposed mechanism:
1. Use and disuse – body parts used extensively
become larger and stronger, those not used
2. inheritance of acquired characteristics
modifications an organism acquires during its
lifetime can be passed to offspring
Credit deserved for his recognition that:
1. Evolution best explanation for both fossil
record and current diversity
2. Recognition of great age of the Earth
3. Emphasis on adaptation to the environment
Charles Lyell (Scottish geologist)
Principles of Geology (1830)
Uniformitarianism (Theory of Uniformity) –
1. Natural laws are constant in space and
2. Most geological change occurs slowly
and gradually, not through sudden,
catastrophic events.
3. Scientists should attempt to explain
events of the past through the same
sorts of natural processes that we
observe today.
• Challenged the view that Earth was
only 6,000 years old
Charles Darwin (1809-1892)
1. Father was wealthy Physician
2. Natural History  interested in
collecting insects, hunting fishing
and reading
3. College
 University of Edinburgh
 studied medicine (age 16)
 transferred to Christ College,
University of Cambridge
 studied theology
 BA in 1831
4. natural theology 
most naturalist and scientists
belonged to the clergy
Darwin’s History
Rev. John Henslow,
Professor of Botany
1831 – H.M.S. Beagle
(Captain FitzRoy)
Professor Henslow
recommended him as
Gave him Lyell's book
Darwin’s Voyage
• At age 22, Charles Darwin began a fiveyear, round-the-world voyage aboard
the HMS Beagle
• As ship’s naturalist, he collected and
examined species that inhabited
regions the ship visited
Voyage of the Beagle
Voyage of the Beagle  5 years
• Darwin spent most of his
time on shore, observing &
collecting exotic and
diverse specimens
Wrote extensively on:
• flora and fauna of So.
(very different from Europe)
• Coral Reefs, Barnacles,
Volcanic Islands
• Volcanic islands
far off coast of
• All inhabitants are
descended from
species that
arrived on islands
from elsewhere
Santa Cruz
Santa Fe
San Cristobal
Galapagos Islands
Darwin’s Finches
Many Endemic Species
Galapagos Turtles
Marine Iguanas
Fossil Evidence
• Darwin found Glyptodont fossils in
• Proposed descent with modification
Descent with Modification
“Like confessing
a murder”
Voyage Ended in 1836
Upon return home to England:
Darwin began discussing his observations
as possible evidence for evolution with
other naturalists
Also read Malthus essay
Thomas Malthus
An Essay of Population (1798)
1837 Darwin read Malthus’
Human population growth
would eventually be limited
• War
• Famine
• Disease
Reproductive Capacity
and Competition
• All populations have the capacity to
increase in numbers
• No population can increase
• Eventually, individuals of a population
end up competing for resources
Galapagos Finches
Galapagos Finches
• Darwin observed finches with 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
and Artificial
Heritable variation – is
random, purposeless, and
in no way subject to
Farmers could not cause
a variation to arise, but
manipulation of existing
variation is possible.
Dog Artificial Selection
Artificial Selection
Variation in Populations
• All individuals have the same genes that
specify the same assortment of traits
• Most genes occur in different forms
(alleles), which produce different
• Some phenotypes compete better
than others (fitness)
Change over Time
• Over time, alleles that produce the most
successful phenotypes will increase in
the population
• Less successful alleles will become less
• Change leads to increased fitness
– Increased adaptation to environment
Natural Selection
• Natural selection for various traits
among individuals of a population
affects which individuals survive and
reproduce in each generation
• Process results in adaptation to the
environment (increases fitness)
Alfred Wallace 1823-1913
British Naturalist
Malay archipelago
• 1858 Darwin received
manuscript with
developed theory of
Natural Selection
 essentially identical
to Darwin’s
• Prompted Darwin to
publish “On the origin of
Darwin quickly finished Origin
of Species, by Means of
Natural Selection (1859)
Darwin received most of the
credit  15 yr. earlier
developed and supported
theory of Natural Select. much
more extensively
Darwin’s success:
science was shifting away
from natural theology
immaculate logic and an
avalanche of evidence
Natural selection is differential success in
Natural selection occurs through an
interaction between the environment and
the variability inherent among individual
organisms making up the population.
The product of natural selection is the
adaptation of populations of organisms to
their environment.