Darwin's voyage on the HMS Beagle and observations of species on the Galapagos Islands led him to develop the theory of natural selection. Natural selection proposes that heritable traits better suited to the environment will help individuals survive and reproduce, leading to evolution over generations as beneficial traits become more common. Darwin published his theory in On the Origin of Species in 1859. Modern evidence from fossils, comparative anatomy, biogeography, and molecular biology provide strong support for evolution by natural selection.

1. Unit 8-Evolution
15.1 Darwin’s Theory of Natural Selection
15.2 Evidence of Evolution
15.3 Shaping Evolutionary Theory
Name _________________________ Period _______

2. 15.1 Darwin’s Theory of Natural Selection
• Main idea:
• Objectives
– Discuss the evidence that convinced Darwin that
species could change over time.
– List the four principles of natural selection.
– Show how natural selection could change a
population
• New Vocabulary
– Selective breeding, Artificial selection, Natural selection,
Evolution

3. Developing the Theory of Natural
Selection
• Charles Darwin boarded the
HMS Beagle in 1831.
• Most believed the world was
about 6,000 years old.
• During the ship’s five year
voyage, Darwin made
extensive collections of
rocks, fossils, plants and
animals.
• He also read Charles Lyell’s Principles of
Geology – a book proposing the Earth was
millions of years old.

4. Developing the Theory of Natural
Selection
• In 1835, the Beagle arrived in the Galapagos
Islands off the coast of South America.
• Darwin began to collect mockingbirds, finches,
and other animals on the four islands.
• He noticed that the different islands seemed
to have their own, slightly different varieties
of animals.
HMS Beagle

5. Developing the Theory of Natural
Selection
• Almost every
specimen that
Darwin had
collected on
the islands was
new to
European
scientists.
• Darwin suspected populations from the mainland
changed after reaching the Galápagos.
Galápagos Islands

6. Developing the Theory of Natural
Selection
• Darwin hypothesized that new species could
appear gradually through small changes in
ancestral species.
• Darwin inferred that if humans could change
species by artificial selection (selective
breeding), then perhaps the same process
could work in nature.

7. Developing the Theory of Natural
Selection
• Darwin called his theory Natural Selection
Natural SelectionNatural Selection
• He reasoned that, given
enough time, natural
selection could modify a
population enough to
produce a new species.

8. Basic Principles of Natural Selection

9. The Origin of Species
• Darwin published On the Origin of Species by
Means of Natural Selection in 1859.
• Today, biologists use the term evolution to
define changes in groups of organisms
through time.
• Darwin’s theory of natural selection is NOT
the same as evolution. Natural selection is a
means of explaining HOW evolution works.

10. 15.2 Evidence of Evolution
• Main idea:
• Objectives:
– Describe how fossils provide evidence of evolution.
– Discuss morphological evidence of evolution.
– Explain how physiology and biochemistry provide
evidence of evolution.
• New Vocabulary

Derived trait

Ancestral trait

Homologous structure

Vestigial structure

Analogous structure

Embryo

Fitness

Mimicry

Camouflage

11. Support for Evolution
• The theory of evolution states that all organisms
on Earth have descended from a common
ancestor.
• The fossil record offers some of the most
significant evidence of evolutionary change.
– Fossils provide a record of species that lived
long ago.
– Fossils show that ancient species share
similarities with species that now live on Earth.

12. • The giant armadillo-like
glyptodont, Glyptodon,is an
extinct animal that Darwin
thought must be related to
the living armadillos of
today.
• The fossil record provides
information for determining
the ancestry of organisms
and the patterns of
evolution.
Support for Evolution
The Fossil Record

13. Support for Evolution
Two major classes of traits:
•Derived traits are newly evolved features,
such as feathers, that do not appear in the
fossils of common ancestors.
•Ancestral traits are more primitive
features, such as teeth and tails, that do
appear in ancestral forms.
The Fossil Record

14. Support for Evolution
• Transitional fossils provide detailed patterns
of evolutionary change for ancestors of many
modern animals, including mollusks, horses,
whales and humans.
Example:
•Archeopteryx

Shares features of
both dinosaurs and
birds.
The Fossil Record

15. Support for Evolution
• Homologous
structures are
anatomically
similar structures
inherited from a
common ancestor.
• The forelimbs of
vertebrates are
adapted for
different uses, but
they all have
similar bones.
• Similar structure; different
function.
Comparative Anatomy

16. Support for Evolution
• Vestigial structures are
the reduced forms of
functional structures in
other organisms.
• Evolutionary theory
predicts that features of
ancestors that no longer
have a function for that
species will become
smaller over time until
they are lost.• Examples: Snake pelvis and
human appendix.
Comparative Anatomy

17. Support for Evolution
• Analogous structures can be
used for the same purpose and
can be similar in construction,
but are not inherited from a
common ancestor.
• Show that functionally similar
features can evolve
independently in similar
environments.
• Different structure; same
function;
Comparative Anatomy

18. Support for Evolution
• An embryo is an early pre-birth stage of an
organism’s development.
• Vertebrate
embryos exhibit
homologous
structures during
certain phases of
development but
become totally
different
structures in the
adult forms.
Comparative Embryology

19. Comparative Biochemistry
• Common
ancestry can
be seen in the
complex
metabolic
molecules that
many different
organisms
share.
Support for Evolution

20. Geographic Distribution
• The distribution of plants and animals that
Darwin saw during his travels first suggested
evolution to Darwin.
Rabbit in Europe Mara in S. America
Support for Evolution

21. • Scientists have confirmed
and expanded Darwin’s
study of the distribution
of plants and animals
around the world in a
field of study now called
biogeography.
• Evolution is intimately linked with
climate and geological forces.
Geographic Distribution
Support for Evolution

22. Adaptation
• An adaptation is a trait
shaped by natural selection
that increases an
organism’s reproductive
success.
• Fitness is a measure of the relative contribution
an individual trait makes to the next generation.
It is often measured as the number of
reproductively viable offspring that an organism
produces in the next generation.

23. • Camouflage allows organisms
to become almost invisible to
predators. Some species have
evolved morphological
adaptations that allow them
to blend in with their
environments.
• Mimicry is another
morphological adaptation
that allows one species to
evolve to resemble another
species.
Adaptation
Types of Adaptation

24. • Antimicrobial resistance
- An antibiotic is a
medicine that slows or
kills the growth of
bacteria.
– Some bacteria have
evolved a resistance
to certain antibiotics.

People infected with resistant bacteria can never get rid of it.
Adaptation
Types of Adaptation

25. 15.3 Shaping Evolutionary Theory
• Main idea:
• Objectives:
– Discuss patterns observed in evolution.
– Describe factors that influence speciation.
– Compare gradualism with punctuated equilibrium.
• Review Vocabulary
– Allele: alternative forms of a character trait that can be
inherited.

26. 15.3 Shaping Evolutionary Theory
• Hardy-Weinberg Principle
• Genetic drift
• Founder effect
• Bottleneck
• Punctuated Equilibrium
• Sexual selection
New Vocabulary

27. Mechanisms of Evolution
• Darwin’s theory of natural selection
remains the central theme of evolution
• Scientists of today know that natural
selection is not the only mechanism of
evolution
• Evolution occurs at the population level,
with genes as the raw material.

28. Mechanisms of Evolution
• Hardy-Weinberg Principle states that when allelic
frequencies remain constant, a population is in
genetic equilibrium.
Population Genetics

Even though the number of owls doubled, the ratio of gray
to red owls remained the same.

29. Mechanisms of Evolution
• p2
+ 2pq + q2
= 1
• This equation allows us to determine the
equilibrium frequency of each genotype in the
population:
• homozygous dominant (p2
)
• heterozygous (2pq)
• homozygous recessive (q2
)
– Note the sum of these frequencies equals one.
Population Genetics

30. Mechanisms of Evolution
A population in genetic equilibrium must meet all five
conditions
•The population is very large
•No immigration or emigration
•Mating is random
•Mutations do not occur (no new variations)
•Natural selection does not occur
Population Genetics

31. • Genetic Drift is a change in the allelic
frequencies in a population that is due to
chance.
• In smaller populations, the effects of genetic
drift becomes more pronounced, and the
chance of losing an allele becomes greater.
• Examples: Founder Effect & Bottleneck
Mechanisms of Evolution
Genetic Drift

32. • Founder Effect occurs when a small sample of a
population settles in a location separated from the
rest of the population
Genetic Drift
• Alleles that were
uncommon in the
original population
might be common in
the new population.
Mechanisms of Evolution
• Alleles that were uncommon in the original
population might be common in the new population.

33. • Bottleneck occurs
when a population
declines to a very
low number and
then rebounds
Mechanisms of Evolution
Genetic Drift

Can decrease
genetic variety.

34. • A population in genetic equilibrium
experiences no gene flow, however, few
populations are isolated
• Random movement of individuals between
populations reduces differences between
populations
Mechanisms of Evolution
Gene Flow

35. • Rarely is mating completely
random in a population.
• Usually individuals mate
with individuals in close
proximity.
Nonrandom mating
Mechanisms of Evolution
• This promotes inbreeding and could lead to a change
in allelic proportions favoring individuals that are
homozygous for particular traits.

36. • A mutation is a random
change in genetic material.
• Occasionally mutations
provide an advantage to
organisms and become more
common in subsequent
generations.
• Basis upon which natural
selection works.
Mechanisms of Evolution
Mutation

37. Select the individuals that are best
adapted for survival and
reproduction
•Stabilizing selection
– eliminate extreme
expressions
• Birth Weights
•Directional selection
– makes organisms more fit.
• Peppered Moths
•Disruptive selection
– process that splits a
population into two groups.
• Lake Erie Water Snakes
Mechanisms of Evolution
Natural Selection

38. • Sexual selection operates in
populations where males and
females differ significantly in
appearance.
– Males are largest and most colorful
in the group
– More likely target for predators yet
bodies enhance reproductive
success
• Examples: Peacocks & Deer
Natural Selection
Mechanisms of Evolution

39. • prevents reproduction
by making fertilization
unlikely.
– Eastern and Western
meadowlarks similar in
appearance but their
mating songs separate
them behaviorally.
Reproductive Isolation
Prezygotic Isolation

40. • Occurs when
fertilization has
occurred but a
hybrid offspring
cannot develop or
reproduce.
Reproductive Isolation
Postzygotic Isolation

A Liger is the offspring of a male lion and
a female tiger. Ligers are sterile.

41. • A physical barrier divides one population into
two or more populations.
Speciation
Allopatric speciation
• For speciation to occur, a population must
diverge and then be reproductively isolated.

42. • Species evolves into a new species without a
physical barrier
Speciation
Sympatric speciation

Apple maggot flies lay
eggs on apples or
hawthorns depending
on the type of fruit the
grew up on.
• For speciation to occur, a population must
diverge and then be reproductively isolated.

43. • Can occur in a relatively short time when one
species gives rise to many different species in
response to the creation of new habitat or some
other ecological opportunity.
Patterns of Evolution
Adaptive Radiation (aka divergent evolution)
• Follows large-
scale
extinction
events

Cichlid fish of
Lake Victoria
in Africa.

44. • The relationship between two species might be so
close that the evolution of one species affects the
evolution of the other species.
• Mutualism – occurs when two species benefit each
other.
Coevolution
Patterns of Evolution

45. • The plant evolves a chemical
defense
• The insects evolve the
biochemistry to resist the
defense
• Response continues to escalate.
Patterns of Evolution
Coevolution
• Coevolutionary arms race – one species can
evolve a parasitic dependency on another
species.
• A plant and an insect that is dependent on the
plant for food

46. • Unrelated species
evolve similar traits
even though they live in
different parts of the
world.
• Occurs in environments
that are geographically
far apart but have
similar ecology and
climate.
Patterns of Evolution
Convergent Evolution

47. • Punctuated
equilibrium
explains rapid
spurts of genetic
change causing
species to diverge
quickly.
Rate of Speciation
Patterns of Evolution
• Evolution proceeds in small, gradual steps =
gradualism.