Charles Darwin developed the theory of evolution by natural selection based on observations from his voyage on the HMS Beagle. He noticed that finches on the Galapagos Islands had adaptations to the individual islands they inhabited. Darwin hypothesized that species slowly change over generations as beneficial genetic variations allow individuals to better survive and pass traits to offspring. His 1859 book On the Origin of Species explained how natural selection acts on genetic variation within populations to produce evolution, sparking scientific and religious controversy.

2. The True Story of the
Theory of Evolution
Or Fitzroy, Fickle Fuegians, and Funny,
Feathered Finches

3. 1973: “Nothing in biology makes sense, except in the
light of evolution.”
-Theodosius Dobzhansky (1900-1975)

4. Evolution, Pre-Darwin
 Beginnings in Ancient Greece
 Species are changeable… Variation occurs!
 Selective breeding utilized already
 “Artificial Selection”
 Widely accepted in early-1800s: Lamarck’s
Theory of Acquired Characteristics

5. Jean-Baptiste de Lamarck
 1744-1829
 1. Individuals lose
characteristics they do
not require (or use) and
develop characteristics
that are useful
 2. Individuals inherit the
traits of their ancestors.

6. Thomas Malthus
 Malthus: An Essay on The
Principles of Populations (1798)
 Populations grow exponentially
while food supply grows linearly.
 Eventually population will
outgrow food supply; life is a
constant struggle
 What keeps a population in
check? War, pestilence, famine,
competition, etc.

7. Charles Lyell
 Principles of Geology
(1830)
 “The present is the key
to the past.”
 Geologic change is the
steady accumulation of
tiny changes over a
lengthy period of time.

9. Charles Robert Darwin
 Born in 1809, same day
as Lincoln
 Wealthy, upper-class
 Father, Robert, was a
physician and anti-
evolutionist
 Grandfather, Erasmus,
was pro-evolutionist and
gifted debater

10. Darwin’s Career
 Robert: “You will be
a disgrace to
yourself and all of
your family”
 Eventually earned a
degree in divinity
from Cambridge

11. The HMS Beagle
 First voyage: May 22,
1826
 Captain Pringle Stokes
 Mission: survey coast
of southern South
America

13. First Voyage of the Beagle
 Stokes – suicide
 Robert Fitzroy
becomes captain:
seeking a literal, biblical
interpretation of
creation
 Boat stolen
 Fuegians captured as
hostages, then returned
to England

14. The Beagle’s Second Voyage
 Darwin – captain’s
companion
 Fitzroy and Darwin –
devoted observers of
the natural world
 IMPORTANT – Darwin
did not SET OUT to
discover natural
selection

15. Darwin’s Finches
 Galapagos islands
(Pacific Ocean)
 Finches uniquely related
to the individual islands
 Ornithologist John Gould
helped Darwin make
his…
 HYPOTHESIS:
Modification of original
group of finches that
colonized islands

16. Megatherium

17. Darwin’s Later Life
 Returned to England in
1836 and never left again
 Suffered frequent
illnesses, probably
tropical in nature
 Married his cousin,
Emma Wedgewood
 Son Charles fell critically
ill in June, 1858

18. Evolution, Post-Darwin
 Wallace sends his
manuscript – 1858
 Darwin faces pressing
dilemma – to present or not
to
 Darwin and Wallace present
together on July 1, 1858
 Around 1900, Mendel’s
papers were “re-
discovered”, as many
scientists attempted to
merge the two theories.Alfred Russell Wallace

19. On the Origin of Species (1859)
 Caused controversy in religious and
scientific communities
 Darwin did not use the term “evolution”
and did not suggest humans descended
from apes
 Questions remained for Darwin… “The
eye to this day gives me a cold shudder...”
 Theory did not gain wide acceptance until
1930s-40s

21. Premises of Natural Selection
1. Populations overproduce.
2. Resources are limited, so
competition ensues.
3. Genetic variations directly
impact the ability of
organisms to survive.

22. Premises of Natural Selection
4. Organisms with beneficial
differences will have a better
chance of survival.
5. Surviving individuals pass
their traits onto future
generations.
6. This results in a slow change
in populations over time.

23. Natural Selection
 process by which
individual organisms
with favorable traits are
more likely to survive
and reproduce
 IMPORTANT –
Individuals do not
evolve. Populations
evolve.

24. KEY DEFINITIONS
 Population: all members of a
species in one area
 Species: Group of organisms that
can produce fertile offspring
 Variation: slight differences among
organisms, often caused through
genetic mutations

25. KEY DEFINITIONS
 Adaptation: Trait that affords
organism a better chance of survival
 Evolution: Gradual change in a
species over time***
 Natural Selection: One mechanism
through which evolution occurs
 Adaptive Radiation: multiple species
descend from one original species
because of selection

26. Darwin’s Mechanisms for Evolution
1. Natural Selection
2. Whatever would
cause “nature” to
select for such a
ridiculous tail on this
peacock?