1. Chapter 15
Darwin’s Theory
of Evolution

2. 15 – 1 The Puzzle of
Life’s Diversity

3. • There are A LOT of different
organisms
• This variety of living things is called
Biological Diversity
Q: What scientific explanation can
account for the diversity of life?
A: A collection of scientific facts,
observations, and hypotheses known
as Evolutionary Theory

4. Evolution
• Change over time

5. Theory
• A well supported testable
explanation of phenomena that
have occurred in the natural world

6. Charles Darwin
• Born in England, February 12, 1809
• Ships naturalist on a trip around the
world aboard the HMS Beagle
• During his travels, Darwin made
numerous observations and collected
evidence that lead him to propose a
revolutionary hypothesis about the
way life changes over time

7. Charles Darwin

8. The Voyage of the Beagle

9. Darwin’s Observations
• Darwin saw far more diversity during his
travels than he saw in his native country

10. Patterns of Diversity
• Darwin was intrigued by the fact that so
many plants and animals seemed
remarkably well suited to whatever
environment they inhabited
• He was also impressed by the ways in
which organisms survived and produced
offspring
• He was also puzzled by where different
species lived and did not live

11. Fossil
• Preserved remains of ancient
organisms
• Some looked like organisms that
were still alive
• Others looked completely unlike any
creature he had ever seen
• Darwin wondered, why had so many
species disappeared, and how were
they related to living species

12. The Galapagos Islands
• Of all the Beagles ports of call, the
one that influenced Darwin the most
was a group of islands off the coast of
South America called the Galapagos
Islands
• Although they were close together
they all had different climates and
differences between the species

13. Galapagos Tortoises

14. The Journey Home
• While heading home, Darwin spent a great
deal of time thinking about his findings
• Darwin observed that the characteristics of
many animals and plants varied noticeably
among the different islands of the
Galapagos
• Darwin began to wonder if animals living
on different islands had once been
members of the same species

15. 15 – 2 Ideas that Shaped
Darwin’s Thinking

16. • To understand how radical Darwin’s
thoughts appeared, you must understand
a few things about the world in which he
lived
• Most Europeans belived the world was
only a few thousand years old
• Nothing had changed since creation
• Rocks and major geological features were
thought to have been produced suddenly
by catastrophic events that humans rarely
ever witnessed
• Slowly after studying many scientific
theories of his time, Darwin began to
change his thinking dramatically

17. Hutton and Lyell
• Geological forces that have shaped Earth
form very slowly, often over millions of
years

18. Hutton and Geological Change
• Geological forces that have
shaped Earth form very slowly,
often over millions of years
• Therefore Earth had to be much
more than a few thousand years
old

19. Lyell’s Principles of Geology
• Charles Lyell – author “Principles of
Geology”
• Process that shaped the Earth
millions of years earlier continue in
the present
• Darwin Thought: If the earth could
change over time, could life be
changing as well?

20. Lamarck’s Evolution Hypothesis
• Jean – Baptiste Lamarck
• French naturalist
• One of the first scientists to recognize that
living things have changed over time, and
that all species were descended from
other species
• Also realized, that organisms were
somehow adapted to their environments

21. Lamarks theory had 3 aspects to it
1. Tendency toward perfection
• Organsims continually change
and acquire features that help
them live more successfully
Ex.) Birds wanted to fly, so their
wings grew and became suited
to flying

22. 2. Use and Disuse
• Body parts that were used developed,
and those that were not went away
Ex.) Reptiles stopped using their legs
and evolved into snakes
3. Evolution of Acquired Traits
• Organsims that changed a
characteristic in their lifetime, would
pass that change on to its offspring

23. • This theory is WRONG!
• He will forever be known in this
class as Lamark the Loser!

24. Population Growth
• Thomas Malthus - English
economist
• Published an essay in which he
noted that babies were being born
faster than people were dying

25. Malthus reasoned
• That if the human population
continued to grow unchecked,
sooner or later there would be
insufficient living space and food
for everyone

26. • Darwin realized that this applied
even more to plants and animals
than it did to humans because
animals and plants had more
offspring than humans did

27. 15 -3 Darwin Presents His
Case

28. Publication of On the Origin of Species
• Darwin did not rush to publish his thoughts
• Darwin was not only stunned by his
discoveries, he was disturbed by them
• In 1858 Alfred Russel Wallace wrote to
Darwin about a theory of evolution that
was similar to his
• Suddenly Darwin had an incentive to
publish his own work

29. Inherited Variation and Artificial
Selection
• One of Darwin’s most important
insights was that members of
each new species vary from one
another in important ways
• Ex.) some trees have bigger fruit,
some cows give more milk

30. Artificial Selection
• Selection by humans for breeding
of desired characteristics

32. Evolution by Natural Selection
• Darwin was convinced that a
process like artificial selection
occurs in nature
• High birth rates and a shortage for
resources would force organisms
into a competition for resources

33. Survival of the Fittest
• A key factor in the struggle for
existence, was how well suited an
organism is to its environment
• Darwin called the ability of an
organism to survive and reproduce in
its environment fitness
• Darwin purposed that fitness is the
result of adaptations

34. Adaptation
• Any characteristic that increases
an organisms chance of survival

35. • Adaptations can be
• Anatomical
– Speed, protection, camouflage
• Physiological
– The way it goes through
photosynthesis
• Behavioral
– The way it hunts

36. • Individuals with low levels of
fitness die and do not reproduce,
and those with high levels of
fitness survive and reproduce
successfully
• He called this process Survival of
the fittest

37. Natural Selection
• Overtime, natural selection results
in changes in the inherited
characteristics of a population.
These changes increase a
species fitness in its environment

38. Descent with Modification
• Darwin proposed that each living
species has descended, with
changes from other species over
time
• He called this Descent with
Modification

39. The Fossil Record
• By comparing fossils from older
rock layers with fossils from
younger layers, scientists could
document the fact that life on
Earth has changed over time

41. Geographical Distribution of Living
Species
• Many species share similar
characteristics because they
inhabit similar environments

43. Homologous body structures
• Structures that have different
forms but develop from the same
embryonic tissue

46. Vestigial structures
• Structures that are reduced in size
and seem to no longer have a
function
Ex.) appendix, tailbone, wisdom teeth
• Scientists think that vestigial
structures are parts that once
functioned in an ancestor

47. Similarities in Embryology
• Many embryos look especially similar
during early stages of development
• All vertebrates go through a stage in
which they have gill pouches
• Similarities suggest an evolutionary
relationship among all vertebrate
species

49. Summary of Darwin’s Theory
1. Individual organisms in nature differ from one
another. Some of this variation is inherited
2. Organisms in nature produce more offspring
than can survive, and many of those that
survive do not reproduce.
3. Because more organisms are produced than
can survive, members of each species must
compete for resources.
4. Because each organism is unique, each has
different advantages and disadvantages in the
struggle for existence.

50. Summary of Darwin’s Theory
5. Individuals best suited to their environment survive and
reproduce most successfully. The characteristics that
make them best suited to their environment are passed
on to offspring. Individuals whose characteristics are not
as well suited to their environment die or leave fewer
offspring.
6. Species change over time. Over long periods, natural
selection causes changes in the characteristics of a
species, such as in size and form. New species arise,
and other species disappear.
7. Species alive today have descended with modification
from species that lived in the past.
8. All organisms on Earth are united into a single tree of life
by common descent.