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Charles Darwin (1809-1882)
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Origin of Species
among the most
influential texts
of this century
Charles Darwin (1809-1882)
• Studied Medicine at Edinburgh
• Switched to become a clergyman
at Christ’s College, Cambridge University
• Passionate interest in Natural History
• Reverend (&Professor) John Henslow
encouraged him to pursue Biology
• In 1831 invited as a naturalist on the HMS
Beagle, a ship sent by British Navy to chart
the waters of South America
HMS Beagle off of
South America
When Darwin left on the Beagle Evolution
was already a popular idea for explaining the
fossil record.
However, there were no known mechanisms
Darwin did not believe in Evolution, but Rev.
Henslow gave him a book to take with him:
Lyell’s Principles of Geology
Historical Context
 By mid-1800s scientific context was in place
for development of theory of Evolution.
 Developments in Geology:
Earth more than 6,000 years old
Fossil Record showed change in species
over time
 The mechanisms for Evolution were missing,
and were hotly debated
Influences on Darwin
• Geology: Darwin had Lyell’s Principles of
Geology on board the HMS Beagle
• Lamarck ’s (1744-1829) Theory of Evolution
Inheritance of acquired characteristics
• Malthus (1766-1834): Competition within
species and struggle for survival
Influences on Darwin
Lyell’s Principles of Geology
• Darwin had Lyell’s book on board the HMS
Beagle, given to him by his botany professor,
Reverend John Henslow
• Fossil record:
• the earth is old
• many animals that once existed are now extinct
• there are layers (strata) in the fossil record show
a pattern of change
Influences on Darwin



Jean-Baptiste Lamarck
(1744-1829)
Proposed most influential
mechanism of evolution before Darwin
Inheritance of acquired characteristics
Introduced the idea of adaptation, but
got the mechanism wrong
http://www.ucmp.berkeley.edu/history/lamarck.html
Influences on Darwin
Malthus (1766-1834):
Essay on the Principles of Population


Competition: not all individuals could
survive
Rate of population growth >> Rate of
increase in food supply
Darwin concluded that individuals that are
better adapted would be the ones that
survive and leave more offspring
• Darwin held on to his work on
natural selection for 20 yrs without
publishing
• Alfred Wallace (1823-1913) came up
with the idea of natural selection
independently
• Darwin rushed to publish Origins in
1859 when he learned of Wallace’s
work
Alfred Russel Wallace (1823-1913)
• “On the
Tendency of
Varieties to
Depart
Indefinitely from
the Original
Type”
• Based on his work
in the Malay
Archipelago
Darwin’s Main Points
(1) Organisms Evolve (Darwin not first)
(2) Common Descent: species arise from common
ancestors
(3) Gradualism: changes are gradual (still debated)
(4) Population Speciation: change in proportions
of individuals having a trait in a population
(Darwin’s original idea)
(5) Natural Selection: mechanism (Wallace also)
***Lamarck vs Darwin***
• Lamarck: inheritance of acquired
traits (not mutations)--Individual
evolution
• Evolution at the Population Level
Lamarck
• Individuals are evolving
• If you got a tan, you’d pass it on
Lamarck
• Individuals are evolving
• If you got a tan, you’d pass it on
Balls get tan
Lamarck
• Individuals are evolving
• If you got a tan, you’d pass it on
Tan balls have offspring that are also tan
Lamarck
• Individuals are evolving
• If you got a tan, you’d pass it on
Some get more tan
Lamarck
• Individuals are evolving
• If you got a tan, you’d pass it on
And then pass on their acquired traits
Darwin
• Natural Selection
Darwin
• Natural Selection
A heritable change
(now known as a
mutation)
Darwin
• Natural Selection
Selection
favors
Darwin
• Natural Selection
Greater
Fitness
Darwin
• Natural Selection
The individuals themselves are not
changing, but the population is the unit
of evolution
Greater
Fitness
Darwin’s unique contribution:
Population Speciation as a result of Natural
Selection
• More offspring are produced than can survive
• Limited resources and competition for resources
• There is variation in a population
• Individuals better adapted to environment survive
• Survivors leave more offspring (“Survival of the Fittest”)
• Thus, average character of population is altered
Galapagos Islands
Darwin’s Mockingbirds
(studied Tortoises and finches later)
"My attention was first thoroughly aroused by
comparing together the various specimens ... of the
mocking-thrush"
~
C. Darwin, The Voyage of the Beagle (1839)
Galapagos Islands
Darwin’s Mockingbirds
Only one species of mockingbird in South
America
 But, on each island there was a different
species
 Mockingbirds on different islands shared
traits that suggested a shared common
ancestor--and were not independently
created

So… Darwin did NOT originate
the idea of Evolution…
… BUT he provided a plausible
Mechanism
… and much evidence
But, Darwin’s theory was not complete
• Because Darwin knew nothing about mutation, he
had no idea how variability was generated in
populations (Lecture 5)
• Because Darwin knew nothing about genetics or
genes, he had no idea how variability was passed
on to offspring (Mendel)
• Darwin did not know about nonadaptive
evolutionary forces, such as Genetic Drift (Lecture 3)
Mendel’s work held part of the key to what
was missing in Darwin’s Theory
• Mendel published in 1865…
was ignored until 1900
• Presented a mechanism for
how traits got passed on
“Individuals pass alleles on
to their offspring intact”
(the idea of particulate
(genes) inheritance)
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