Descent with Modification – A
Darwinian View of Life
Chapter 22
A.P. Biology
Liberty Senior High School
Rick L. Knowles
• Concept 1.4: Evolution accounts for life’s
unity and diversity
• The history of life
– Is a saga of a changing Earth billions of years old
Figure 1.17
Theodosius Dobzhansky
“Nothing in biology makes sense
except in the light of
evolution.”
The American Biology Teacher (1973)
• Overview: Darwin Introduces a Revolutionary
Theory
• A new era of biology began on November 24,
1859
– The day Charles Darwin published On the Origin of
Species by Means of Natural Selection
Charles Darwin, 1831, age 22,
starting his voyage on the HMS
Beagle
• Concept 22.1: The Darwinian revolution
challenged traditional views of a young Earth
inhabited by unchanging species
• In order to understand why Darwin’s ideas were
revolutionary
– We need to examine his views in the context of other
Western ideas about Earth and its life
• The historical context of Darwin’s life and ideas
Fig. 22.2
The Scale of Nature and Classification
of Species
• The Greek philosopher Aristotle
– Viewed species as fixed and unchanging
• The Old Testament of the Bible
– Holds that species were individually designed by
God and therefore perfect
– “Intelligent Design”
• Carolus Linnaeus
– Interpreted organismal
adaptations as evidence that
the Creator had designed
each species for a specific
purpose
– Was a founder of taxonomy,
classifying life’s diversity
“for the greater glory of
God”
– Viewed species similarities
not as evolutionary
relationship, but as patterns
of creation.
Carolus Linnaeus, 1707 -1778
Fossils, Cuvier, and Catastrophism
• The study of fossils
– Helped to lay the groundwork for Darwin’s ideas
• Fossils are remains or traces of organisms from
the past
– Usually found in sedimentary rock, which appears in
layers or strata
Figure 22.3
• Paleontology, the study of fossils
– Was largely developed by French scientist Georges
Cuvier
– Observed that upper strata were younger and lower
strata were older
– Noticed that new species would appear in an older
strata and then disappear in a newer strata.
• Cuvier opposed the idea of gradual evolutionary
change
– And instead advocated catastrophism, speculating
that each boundary between strata represents a
catastrophe (flood or drought).
Theories of Gradualism
• Gradualism
– Is the idea that profound change can take place
through the cumulative effect of slow but continuous
processes.
– 1795, James Hutton proposed that Earth’s geologic
features could be explained by gradual mechanisms
currently operating (ex. valleys are created by
rivers)
• Geologists Hutton and
Charles Lyell
Charles Lyell, 1797-1875
– Perceived that changes in
Earth’s surface can result
from slow continuous
actions still operating
today
– Lyell proposed
uniformitarianism – same
geologic processes are
operating today as in the
past and at the same rate.
– Exerted a strong influence
on Darwin’s thinking
One of the First “Ideas” of Evolution
Jean-Baptiste de Lamarck, 1744 - 1829
• Lamarck compared
species today with the
fossil record.
• 1809, hypothesized that
species evolve through
use and disuse and the
inheritance of acquired
traits.
• Organisms have an innate
drive to become more
complex.
• But the mechanisms he
proposed are
unsupported by evidence
Lamarck’s View of
Evolution
• Plants and animals
changed over time
through the use and
disuse of certain
characteristics.
• These acquired
characteristics were
inherited by the next
generation.
• No support for this
notion.
Darwin and the HMS Beagle
• During his travels
– Darwin observed and collected
many specimens of South
American plants and animals
• Darwin observed various
adaptations of plants and
animals
– That inhabited many diverse
environments
Charles Darwin, 1831, age 22,
starting his voyage on the
HMS Beagle
Fig. 22.5 The Voyage of the HMS Beagle
Name Two (2) Observations that
Darwin Made Leading to His
Theory.
Name One (1) Observation
We’ve Since Made About the
Natural World.
Darwin’s Observations about Evolution
• 1. Fossil Record: noticed that the
fossils of South America
resembled living species of that
continent.
• Example: Glyptodon related to
modern armadillo?
Glyptodon
Modern
Armadillo,
Omaha Zoo,
2009
Darwin’s Observations of Evolution
• 2. Biogeography – plants and animals
in temperate regions of South America
resemble tropical species in South
America than the temperate species in
Europe.
• The distribution of life across similar
climates is not always the same;
(climate alone is not causing diversity).
• Closely related species are found in
same geographic region.
• Different geographic regions, different
mammalian “brands”
– Have evolved independently from different ancestors
Marsupial
Mammal
NORTH
AMERICA
Sugar
glider
AUSTRALIA
Flying
squirrel
Figure 22.17
Placental Mammal
Charles Darwin, 1835, Galapagos
What’s so special about a bunch
of islands?
National Geographic Series
Galapagos,
Tape #254
Darwin’s Finches
The Galapagos Archipelago
Bartoloma Island
Isabela Island
• Darwin proposed that natural selection
– Could enable an ancestral species to “split”
into two or more descendant species,
resulting in a “tree of life”
Large
ground finch
Large cactus
ground finch
Small
ground
finch
Large
tree finch
Camarhynchus
Green
Geospiza
Gray
Geospiza
magnirostris
psitacula
warbler
warbler
Sharp-beaked
fuliginosa
Woodpecker Medium
Geospiza Medium
finch
finch
tree finch
ground finch
finch
conirostris ground
finch
Certhidea Certhidea
Geospiza Cactus
Cactospiza Camarhynchus olivacea fusca
difficilis ground finch
pauper
pallida
Geospiza Mangrove
Small tree finch
finch
fortis
Geospiza
Camarhynchus
Cactospiza
scandens
parvulus
heliobates
Vegetarian
Cactus flower
Seed eater
Seed eater
finch
eater
Platyspiza
crassirostris
Insect eaters
Ground finches
Figure 1.23
Tree finches
Bud eater
Warbler finches
Common ancestor from
South American mainland
Large
ground finch
Large cactus
ground finch
Geospiza
magnirostris
Geospiza
conirostris
Woodpecker
finch
Medium
ground
finch
Cactus
ground finch
Cactospiza
pallida
Geospiza
fortis
Geospiza
scandens
Seed eater
Camarhynchus
psitacula
Geospiza
fuliginosa
Sharp-beaked
ground finch
Geospiza
difficilis
Large
tree finch
Small
ground
finch
Cactus flower
eater
Green
warbler
finch
Medium
tree finch
Certhidea
olivacea
Camarhynchus
pauper
Mangrove
finch
Gray
warbler
finch
Certhidea
fusca
Small tree finch
Camarhynchus
parvulus
Cactospiza
heliobates
Vegetarian
finch
Seed eater
Platyspiza
crassirostris
Insect eaters
Ground finches
Figure 1.23
Tree finches
Bud eater
Warbler finches
Common ancestor from
South American mainland
Seen one tortoise, you’ve seen them
all?
Dome-shaped Carapace
Saddle-shaped Carapace
Galapagos Tortoise Distribution
Galapagos tortoise distribution, Galapagos Islands. Redrawn from
Iverson (1992).
Galapagos Tortoise-Env. Club
2008, Omaha Zoo
Darwin’s Focus on Adaptation
• Years later, Darwin
reassessed all that
he had observed
during the voyage
of the Beagle
• He began to
perceive
adaptation to the
environment and
the origin of new
species as closely
related processes
Fig. 22.6
Alfred Russel Wallace, 1823-1913
•Explored
Indonesia and
southeast Asia,
from 1854-1861,
•Observed
Tigers, Orangs,
and Rhinos, Oh
My!
Indian Rhino
Sumatran Rhino
Javan Rhino
Other Observations about Evolution
• 3. Artificial Selection - humans have modified
other species over many generations by selecting
and breeding individuals that possess desired traits
Fig. 22.10
• The Origin of Species articulated two
main points…
– Descent with modification
– Natural selection
Figure 1.19
Natural Selection
• Darwin proposed natural selection
– As the mechanism for evolutionary adaptation
of populations to their environments
Population
of organisms
Hereditary
variations
Overproduction
and struggle for
existence
Differences in reproductive
success
Figure 1.20
Evolution of adaptations
in the population
• Natural selection is the evolutionary process that
occurs…
– When a population’s heritable variations are exposed
to environmental factors that favor the reproductive
success of some individuals over others.
1
Populations with varied inherited traits
2 Elimination of individuals with certain traits.
3 Reproduction of survivors.
Figure 1.21
4 Increasing frequency of traits that enhance
survival and reproductive success.
The Origin of Species
• Darwin developed two main ideas
– Evolution explains life’s unity and diversity
– Natural selection is a cause of adaptive evolution
• The phrase descent with modification
– Summarized Darwin’s perception of the unity of life
– States that all organisms are related through descent
from an ancestor that lived in the remote past
Elephant Phylogeny
Fig. 22.7
Summary of Natural Selection
• Natural selection is differential success in
reproduction
– That results from the interaction between individuals
that vary in heritable traits and their environment
• If an environment changes over time
– Natural selection may result in adaptation to these
new conditions
• Over time natural
selection can
produce an
increase
– In the
adaptation of
organisms to
their
environment
Fig. 22.11
• Concept 22.3: Darwin’s theory explains a wide
range of observations
• Darwin’s theory of evolution
– Continues to be tested by how effectively it can
account for additional observations and experimental
outcomes
– Natural Selection in Action – Evolution continues
today!
• Guppies
• HIV
• Humans
Differential Predation in Guppy
Populations
• Researchers have observed natural selection
– Leading to adaptive evolution in guppy populations
EXPERIMENT Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools
and measured the average age and size of guppies at maturity over an 11-year period (30 to
60 generations).
Pools with killifish,
but not guppies prior
to transplant
Predator: Killifish; preys
mainly on small guppies
Experimental
transplant of
guppies
Guppies:
Larger at
sexual maturity
than those in
“pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on large guppies
Guppies: Smaller at sexual maturity than
those in “killifish pools”
Figure 22.12
RESULTS
After 11 years, the average size and age at maturity of guppies in the transplanted
populations increased compared to those of guppies in control populations.
185.6
85.7 92.3
161.5
Control Population: Guppies
from pools with pike-cichlids
as predators
58.2
48.5
67.5 76.1
Males
CONCLUSION
Females
Males
Females
Experimental Population:
Guppies transplanted to
pools with killifish as
predators
Reznick and Endler concluded that the change in predator resulted in different variations
in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered
selection pressure resulted in an observable evolutionary change in the experimental population.
The Evolution of Drug-Resistant
HIV
• In humans, the use of drugs
– Selects for pathogens that through chance mutations
are resistant to the drugs’ effects
• Natural selection is a cause of adaptive evolution
Anatomy of HIV
Inside HIV
• Researchers have developed numerous drugs to
combat HIV
– But using these medications selects for viruses
resistant to the drugs
Figure 22.13
New Evidence that
Darwin Did Not Have
• How old did most 19th Century
people believe the Earth was?
• About 6,000 years old (Cuvier’s
young Earth)
• 1. Age of the Earth- 4.5 billion
year old. Better dating techniques
than in Darwin’s time; more
complete fossil record.
2. Transitional Species
• Have intermediate characteristics of
two groups of animals – may represent
a link in evolution (missing link?).
• Changes in structures may be small –
difficult to identify in fossils.
• Species replaced quickly – not
common in fossil record.
Archaeopteryx (150 million years ago)
Archaeopteryx
Archaeopteryx at the KU Natural
History Museum
Evolution Happens in
Small Steps
Show me the frogs!
Discover- Weird Nature:
Marvelous Motion, tape #55
Other Transitional Examples?
Rodhocetus
balochistanensis
Modern
Whales
A Walking Whale?
Ambulocetus natans
Transitional
Skulls
Rodhocetus Foot
Transitional Diatoms in Yellowstone
3. Vestigial Structures
• Existing structures that have no
apparent function, but resemble
structures of presumed ancestors.
• Examples: human appendix;
muscle set in humans for moving
ears;
The “Pelvis” of a Whale
Evidence of Transitional
Species Today!
Vestigial Structure- blue whales
with femurs?
Life of Mammals-Return to the
Water video, tape #110
Vestigial Organs in Humans?
Structures of little or no use but may
represent historical remnants of
structures that had important
functions in ancestors.
Vermiform Appendix
Goosebumps?
Vomeronasal or Jacobson’s Organ
“Junk”DNA; L-gulonolactone oxidase
gene
Extra Ear Muscles – auriculares
muscles
Plantaris Muscle – 9% don’t have it
Wisdom Teeth – mandible becoming
smaller
Third Eyelid – Plica semilunaris
Darwin’s (Auricular) Tubercle – only
10.4% have it.
Coccyx
Four-Finned Dolphin; Oct, 2006
Divers hold a
bottlenose dolphin
which has an extra
set of human
palm-sized fins
near its tail in Taiji,
Wakayama
prefecture in
western Japan.
-USA Today, Nov.
6, 2006
Four-Finned Dolphin; Oct, 2006
Divers hold a
bottlenose dolphin
which has an extra
set of human palmsized fins near its tail
in Taiji, Wakayama
prefecture in western
Japan.
-USA Today, Nov. 6,
2006
Show me more vestigial
structures!
Do snakes have “feet”?
The story of boas and
pythons.
4. Anatomical Homologies
• Homologous structures between organisms
– Are anatomical resemblances that represent
variations on a structural theme that was present in a
common ancestor
Human
Figure 22.14
Cat
Whale
Bat
Homology
• Homologous Structures – structures in different
species that are similar because of commons
ancestry.
Sophie and a Mosasaur
Analogy
• Analogous Structures – similarity in structures due
to adaptations from similar evolutionary pressures
(convergent evolution) and not a common ancestor.
• The products of natural selection
– Are often exquisite adaptations of organisms to
the special circumstances of their way of life
and their environment
Figure 1.22
5. Comparative Embryology
– Reveals additional anatomical homologies not visible
in adult organisms
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Figure 22.15
Human embryo
Show me an example of
homologous structures!
Compare a human hand
and bat wing.
Life of Mammals- Life
in the Trees video, tape
#110
6. Molecular Homologies
• Biologists
observe
homologies
among
organisms at the
molecular level
– Genes and
proteins that are
shared among
organisms
inherited from a
common
ancestor.
Fig. 22.16
Darwin’s Theory of Evolution
• Natural selection is the driving
force of changes within species
populations.
Can we see evolution?
• Weiner, J. 1994. The Beak of
the Finch. Knopf, New York.
• The video “What Darwin
Never Saw”
I want to see evolution in
action!
Scientific American
Frontiers-Voyage to the
Galapagos, 2000, VT 551.4
SCI