Charles Darwin developed the theory of evolution by natural selection based on observations and evidence from his voyage on the HMS Beagle. He proposed that (1) natural variation exists between individuals of a species, (2) there is a struggle for existence as members of a species compete for limited resources, and (3) the individuals best suited for their environment (the fittest) will survive and pass on their traits, leading to the evolution of species over time. Darwin provided evidence from fossils, biogeography, embryology, and homologous structures to support his theory of common descent and evolution.

1. Chapter 15: Darwin’s
Theory of Evolution
Pages 368-386

2. Chapter 15-1: The Puzzle
of Life’s Diversity
Pages 369-372

3. Vocabulary 15-1
evolution
theory
fossil

4. Evolution
Definition: change over time, the
process by which modern organisms
have descended from ancient
organisms

5. The Theory of Evolution
helps us understand how:
• fossils fit into life’s history
• bacteria become resistant to
antibiotics & insects to pesticides
• determine the relationships among
the different groups of organisms on
Earth

6. Charles Darwin
• Born Feb.12, 1809 in England
• Sailed on the H.M.S. Beagle in
1831 for a 5 year voyage around the
world
• Made many observations & collected
evidence that caused him to
hypothesize about how life changes
over time
• His observations were influenced by
reading the ideas of other scientists

7. Charles Darwin

9. Scientific beliefs before
Darwin:
• Species were unchanging – the same
organisms always existed.
• Earth was about 10,000 years old.

10. Darwin’s Observations
1. A large variety of organisms inhabit the
Earth
• Example: He collected 68 species of
beetles in 1 day in a rainforest in Brazil
2. Organisms were well suited for the
different environments in which they were
found
• Examples: On the Galapagos Islands, t ortoises
from different islands have different shaped
shells & neck lengths and different finches (birds)
have different shaped beaks

11. Fossils
• Definition: preserved remains of ancient
organisms
• Fossil evidence raises many questions:
• Why have so many species disappeared?
• How do extinct organisms relate to living
organisms?
• Darwin based most of his beliefs on the
fossils he found and wondered if animals
on different islands once belonged to the
same species

12. Review: Species
Definition: organisms belong to the
same species if they can interbreed
(produce fertile offspring) under
natural conditions

13. Good News:
We are skipping
Chapter 15-2.

14. To summarize Chapter
15-2:
Many scientists contributed ideas that
helped frame Darwin’s theory, ideas such
as:
3) The Earth is actually millions of years
old and is still changing…
4) Organisms acquired or lost certain traits
during their lifetime that could be passed
onto offspring, thus changing a species
(later proved false)…
5) If a population grows unchecked, sooner
or later, food and space will run out…

15. Chapter 15-3: Darwin
Presents His Case
Pages 378-386

16. Vocabulary 15-3
natural variation
struggle for existence
fitness
adaptation
survival of the fittest
natural selection
common descent
homologous structure
vestigial organ

17. Darwin’s Book
• Darwin collected his ideas and
published the book “On the
Origin of Species” which
proposed:
– A mechanism of evolution he called
natural selection, based on three
major principles
– That the process of evolution has
been taking place for millions of
years

18. Principle #1: Natural
Variation
• Definition: differences among
individuals of a species
• Darwin argued that natural variation
is found in all species
• These “variations” can be passed on
to the next generation

19. These natural variations occur
through:
• Sexual reproduction
• Independent assortment of
chromosomes
• Segregation of alleles
• Crossing-over during meiosis
• Mutations in DNA

20. Principle #2: Struggle for
Existence
Members of each species compete
for living space, food, and other
things needed for them to:
SURVIVE AND
REPRODUCE.

21. Principle #3: Survival of the
Fittest
1) The greater fitness an organism has, the
more likely it is to survive in an
environment (i.e. “win the struggle”).
Fitness: is the ability of an organism to survive and
reproduce in an environment
2) Fitness is the result of adaptations .
Adaptations: any inherited characteristic that
increases an organism’s chance of survival
• Example: can be physical (porcupine quills) or
behavioral
(hunting in a pack)

22. Darwin’s Theory of Evolution
by Natural Selection
• Individuals with high levels of
fitness survive and reproduce the
most offspring – survival of the
fittest.
• Individuals not suited to their
environment (low fitness) either
die or produce small number of
offspring.

23. Common Ancestry
• Definition: all living organisms are
related to one another
• Common descent: all species –
living and extinct – came from
common ancestors

24. Evidence for
Evolution

25. 1. The Fossil Record
• Fossil: preserved remains of an ancient
organism; formed by sediment settling over
remains
• Fossil records are incomplete – many
organisms have lived and died and were
never preserved
• Fossils in the same layer of rock lived at
the same time
• Shows how some organisms change slowly
over time
• Show how complex animals and plants of
today were preceded by simpler ones

28. The “fishapod”…375 million years old…may
be the link between water and land.

29. “Ida”…47 million years old…possibly the
missing link in primate evolution.

31. 2. Geographic Distribution of
Species
• Isolated land areas and island groups
evolve their own distinct plants and
animals fit to the environment
• The same kinds of fossils are found
in areas which were once connected
(ex. Pangaea, the “supercontinent”)
but now separated as a result of
continental drift

34. 3. Homologous Body
Structures & Vestigial
Organs
• Many different organisms have similar
body structures – which may perform
different functions but are
constructed of the same basic bones
and tissues
• Vestigial organ: organ that is so
reduced in size it does not perform a
function

37. 4. Embryonic Development
• Embryos of closely related organisms
have similar early stages of
development

39. 5. Molecular Analysis
• If two species have genes and
proteins sequences that match
closely, biologists conclude that the
sequence was copied from a relatively
recent common ancestor