Darwin proposed that evolution occurs through natural selection, where organisms better adapted to their environment are more likely to survive and pass on their traits. He reached this conclusion based on observations from his voyage on the HMS Beagle of fossils, biogeography of the Galapagos Islands, and how species were suited to their environments. Evidence from fossils, anatomical similarities between species, molecular biology, and biogeography provide strong support for Darwin's theory of evolution by natural selection.

1. Chapter 14
Darwin and
Evolution
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2. 14.1
Darwin’s
Theory
of
Evolution
• In this section, the following
objective will be covered:
• Explain Darwin's theory of natural
selection and how his study of
fossils and biogeography
contributed to the theory.
• Differentiate between natural and
artificial selection.
• Define and identify adaptations in
organisms.
• Describe how natural selection can
lead to adaptation, which ultimately
leads to the evolution of a species.

3. Charles
Darwin
•Charles Darwin was 22 in 1831.
•Naturalist aboard the HMS Beagle
•Five year voyage through Southern
Hemisphere
•Mission to expand navy’s
knowledge of natural resources
(water and food) in foreign lands
•Observation led Darwin to
conclude that biological evolution
occurs.
• Contrary to current beliefs of his time

4. Voyage of the
HMS Beagle

5. Before Darwin
•People had an entirely different way of viewing the world.
• Earth was only a few thousand years old.
• Species remained the same since creation.
•Explorers brought back fossils (remains of once-living organisms) found in
strata (layers of rock or sedimentary material).
•Georges Cuvier founded paleontology.
• Study of fossils
• He believed in fixity of species, yet strata showed a succession of different
forms over time.
• Catastrophism—explains appearance of new forms as replacing old forms
due to local catastrophe

6. Strata in Rock
Visible strata © Doug Sherman/Geofile

7. Before Darwin
•Jean-Baptiste de Lamarck
• Evolution occurred and adaptation was the cause of diversity.
• Concluded more complex forms descended from less complex forms
• Inheritance of acquired characteristics
• Use and disuse of a structure can bring about inherited change.
• Long neck in giraffes developed from stretching to reach food.
• Not supported—people who were blinded in an accident would have
blind children
• Modern genetics—phenotypic changes acquired during the lifetime do
not result in genetic changes that can be passed to offspring

8. Lamarck vs. Darwin
Darwin’s ideas were close to Lamarck,
BUT
• Species are suited to the environment
through no will of their own.
• Natural selection is the means for
speciation.

9. Darwin’s
Conclusions
Based upon
Three Main
Factors:
Geology,
Fossils, and
Biogeography
• Darwin collected fossils during
his voyage that differed from
modern forms.
• Once he accepted that the
Earth must be very old, he
began to think there was time
for descent with modification
(evolution) to occur.
• Species are not fixed but
change over time.

10. Fossils in
Strata

11. Fossils Discovered by Darwin

12. Darwin’s
Conclusions
Based Also
upon
Biogeography
•Study of biogeography
• Study of the distribution of
life-forms on Earth
• Compared animals of South
America to England
• Did the Patagonian hare
resemble a rabbit because
the two types of animals
were adapted to the same
environment?
• Convergent evolution

13. The Patagonian Hare and European Rabbit

14. Observations of Biogeography
Galápagos Islands—off the coast of South America
• Too far from mainland for most terrestrial plants and
animals to colonize
• Species there slightly different from mainland forms
• Where did they come from? Why are they different?

15. Observations of Biogeography
Finches
• Some were like mainland finches, others quite different
• Ground-dwelling finch beak size dependent on seed they eat
• Tree-dwelling finch beak size and shape dependent on their insect
prey
• Could have descended from a mainland finch
• Speciation—formation of a new species—occurred because the
isolated population evolved independently of the mainland
population.

16. Galápagos
Finches
a: © Miguel Castro/Science Source; b: © David Hosking/Alamy; c: © Michael Stubblefield/Alamy RF
a.Ground-
dwelling finch
b.Woodpecker finch
c.Cactus finch

17. Observations of Biogeography
Galápagos Islands tortoises
• Each island also had its own type of tortoise.
• Long-necked tortoises in dry areas where food scarce
• Short-necked tortoises in moist regions with abundant food
• Adaptation—any characteristic that makes an organism more suited
to its environment

18. Natural Selection and Adaptation
• Mechanism for evolution
• Process that results in the evolution of organisms well adapted to their
environment
• Requires:
• Members of a population to have heritable variation
• More offspring produced than can be supported
• Individuals with favorable traits survive and reproduce more than those
lacking the traits.
• Across generations, a larger proportion of the population possesses the
favorable traits and become adapted to the environment.

19. Natural Selection
and Adaptation
•Uses only variations
resulting from genetic
changes
• No direction or
anticipation of future
needs
•Ongoing process—as
environment changes,
suitability of adaptations
changes

20. Organisms Vary in Their Traits
• Prior to Darwin, variations were
considered imperfections and ignored.
• Variations are essential to Darwin’s natural
selection process.
• Genes, together with the environment,
determine phenotype.
• Mutations, chromosomal rearrangements,
and assortment of chromosomes during
meiosis and fertilization can cause new
variations to arise.

21. Organisms
Struggle to
Exist
• Thomas Malthus said death
and famine are inevitable
because the human population
increases faster than the food
supply.
• Darwin applied this to all
organisms.

22. Organisms
Differ in
Fitness
•Fitness—reproductive success of an
individual relative to other members
of the population
• Determined by comparing the
number of surviving fertile
offspring produced by each
member of a population
•Most-fit individuals capture the most
resources and convert into a larger
number of viable offspring.
•What determines fitness varies for
different populations.
•Artificial selection—humans choose
particular traits
•In nature, interaction with the
environment determines fitness.

23. Mechanism
of
Evolution
Lamarck’s proposal
Originally, giraffes had
short necks.
Giraffes stretched their necks
in order to reach food.
With continual stretching,
most giraffes now have
long necks.
Darwin’s proposal
Originally, giraffe
neck length varied.
Struggle to exist causes
long-necked giraffes to have
the most offspring.
Due to natural selection,
most giraffes now have
long necks.

24. Organisms
Become
Adapted
•An adaptation may take many
generations to evolve.
•Manatees, penguins, and sea
turtles all have flippers to move
through the water.
• Convergent evolution
•Natural selection causes adaptive
traits to be increasingly
represented in succeeding
generations.
•Only natural selection results in
adaptation to the environment.

25. Darwin and Wallace
After the HMS Beagle retuned to England in 1836, Darwin
waited 20 years to publish On the Origin of Species.
• Gathered evidence to support his hypothesis
• Prompted to publish after reading similar hypothesis by Wallace
Alfred Russel Wallace
• Also an English naturalist and collector at home and abroad
• Conceived idea of “survival of the fittest”
• Sent essay to Darwin for comment
Joint paper presented to Linnean Society
• Darwin presented an abstract of On the Origin of Species.
• Wallace presented “On the Tendency of Varieties to Depart Indefinitely
from the Original Type.”
• Announced to the world that species evolve through natural selection
with common descent

26. Wallace’s Line
and
Biogeography

27. 14.2
Evidence
of
Evolution
ary
Change
• In this section, the following
objective will be covered:
• Explain how the fossil record,
biogeographical evidence,
comparative anatomy, and
biochemistry support evolutionary
theory.

28. Evidence of Evolutionary Change
• The theory of evolution states that all living things have a
common ancestor, but each is adapted to a particular way of
life.
• Hypotheses become a scientific theory only when a variety of
evidence from independent investigators supports the
hypothesis.
• Theory of evolution is a unifying theme in biology because it
can explain so many different observations in various fields
of biology

29. Fossil
Evidence
• Fossils trapped in rock strata are the
fossil record that tell us about the
history of life.
• Succession of life-forms from the
simple to the more complex
• Find transitional links between
groups
• Archaeopteryx fossils intermediate
between reptiles and birds.
• Evolution of tetrapods and whales

30. Re-creation
Archaeopteryx

31. Evolution of
Tetrapods

32. Evolution
of
Whales
Hypothetical
mesonychid
skeleton
Modern toothed whales
The reduced hindlimbs of Rodhocetus Kasrani
could not have aided it in walking or
swimming. Rodhocetus swam with an up-and-
down motion, as do modern whales.
Ambulocetus natans
probably walked on land (as do
modern sea lions) and swam by
flexing its backbone and paddling with its
hindlimbs (as do modern otters).

33. Biogeographical Evidence
•Study of distribution of organisms throughout the world
•Distribution consistent with hypothesis that, when forms are related, they evolved in one locale
and then spread to accessible regions
•Darwin noted that South America lacks rabbits even though the environment is suitable.
• Rabbits evolved elsewhere and had no means of reaching South America.
•South America, Antarctica, and Australia connected long ago.
• Marsupials and placental mammals arose at that time.
• Marsupials only plentiful in Australia because it drifted away, separating them from
competition with placental mammals
• Opossum only marsupial in the Americas
•In some cases marsupial and placental mammals resemble each other.
• Supports hypothesis that evolution is influenced by environment

34. Marsupials of Australia
Sugar glider, Petaurus breviceps, is a tree-
dweller and resembles the placental
flying squirrel.
The Australian wombat, Vombatus, is
nocturnal and lives in burrows. It
resembles the placental woodchuck.
The Tasmanian wolf (now extinct) was
a carnivore that resembled the American
wolf.
(sugar glider): © A.N.T. Photo Library/Science Source; (wombat): © Photodisc Collection/Getty RF;
(Tasmanian tiger): © World History Archive/Alamy

35. Anatomical
Evidence
Vestigial structures
• Anatomical features that are fully
developed in one group of organisms
but reduced and nonfunctional in other
similar groups
• Most birds have well-developed wings;
ostriches do not.
• Whales and snakes have remnants of
hip bones and legs.
• Humans have a tailbone.
• Presence explained by common descent
hypothesis

36. Anatomical
Evidence
Homologous structures
• Anatomically similar structures are
explainable by inheritance from a
common ancestor.
• All vertebrate forelimbs contain the
same set of bones organized in similar
ways despite dissimilar functions.
• Analogous structures—structures serve
the same function but are not
constructed similarly—bird and insect
wings

37. Significance of Structural Similarities:
Bird and Bat

38. Significance of
Structural
Similarities:
Whale and Cat

39. Significance
of Structural
Similarities:
Horse and
Human

40. Homology
•Homology shared by vertebrates
extends to their embryological
development.
• At some time during development, all
vertebrates have a postanal tail and paired
pharyngeal pouches.
• In fishes and amphibian larvae, pouches
develop into functioning gills.
• In humans, the first pair of pouches becomes
cavity of middle ear and auditory tube, the
second pair becomes tonsils, and the third and
fourth pair become thymus and parathyroid
glands.
• New structures originate by modifying
preexisting structures of one’s ancestors.

41. Significance of Developmental Similarities
(pig & chick): © Carolina Biological Supply/Phototake

42. Molecular Evidence
•All living organisms use the same biochemical molecules, including DNA,
ATP, and many nearly identical enzymes.
•Many developmental genes (Hox) are shared in animals ranging from
worms to humans.
•Life’s vast diversity has come about from only slight differences in the
same genes.
•Cytochrome c is a molecule used in the electron transport chain of all
organisms.
• Data on the amino acid sequence demonstrate that the sequence varies
consistent with other data regarding anatomical similarities, and
therefore show relatedness.

43. Significance
of
Biochemical
Differences

44. Chapter 14 Objective Summary
• You should now be able to:
• 1. Explain Darwin's theory of natural selection and how his study
of fossils and biogeography contributed to the theory.
• 2. Differentiate between natural and artificial selection.
• 3. Define and identify adaptations in organisms.
• 4. Describe how natural selection can lead to adaptation, which
ultimately leads to the evolution of a species.
• 5. Explain how the fossil record, biogeographical evidence,
comparative anatomy, and biochemistry support evolutionary
theory.