Darwin's revolutionary theory of evolution by natural selection

Chapter 22

Descent with Modification: A
Darwinian View of Life

PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece

Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• 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


• The Origin of Species
– Focused biologists’ attention on the great
diversity of organisms

Figure 22.1


• Darwin made two major points in his book
– He presented evidence that the many species
of organisms presently inhabiting the Earth are
descendants of ancestral species
– He proposed a mechanism for the evolutionary
process, natural selection


• 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
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, nutural selection)
Mendel (inheritance)
Wallace (evolution, natural selection)
American Revolution French Revolution U.S. Civil War
1750 1800 1850 1900
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his theory of evolution.
1830 Lyell publishes Principles of Geology.
1831–1836 Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks on the origin of species.
1844 Darwin writes his essay on the origin of species.
1858 Wallace sends his theory to Darwin.
1859 The Origin of Species is published.
1865 Mendel publishes inheritance papers.

Figure 22.2


Resistance to the Idea of Evolution
• The Origin of Species
– Shook the deepest roots of Western culture

– Challenged a worldview that had been
prevalent for centuries


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


• 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”


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

• Cuvier opposed the idea of gradual
evolutionary change
– And instead advocated catastrophism,
speculating that each boundary between
strata represents a catastrophe


Theories of Gradualism
• Gradualism
– Is the idea that profound change can take
place through the cumulative effect of slow but
continuous processes


• Geologists Hutton and Lyell
– Perceived that changes in Earth’s surface can
result from slow continuous actions still
operating today
– Exerted a strong influence on Darwin’s thinking


Lamarck’s Theory of Evolution
• Lamarck hypothesized that species evolve
– Through use and disuse and the inheritance of
acquired traits
– But the mechanisms he proposed are
unsupported by evidence

Figure 22.4

• Concept 22.2: In The Origin of Species, Darwin
proposed that species change through natural
selection
• As the 19th century dawned
– It was generally believed that species had
remained unchanged since their creation, but a
major change would challenge this thinking


Darwin’s Research
• As a boy and into adulthood, Charles Darwin
– Had a consuming interest in nature

• Soon after Darwin received his B.A. degree
– He was accepted on board the HMS Beagle,
which was about to embark on a voyage
around the world


The Voyage of the Beagle
• During his travels on the Beagle
– 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


• Darwin’s interest in the geographic distribution
of species
– Was kindled by the Beagle’s stop at the Galápagos
Islands near the equator west of South America

England
EUROPE
NORTH
AMERICA
PACIFIC ATLANTIC
OCEAN OCEAN

Galápagos AFRICA HMS Beagle in port
Islands

SOUTH
Darwin in 1840, AMERICA
after his return
AUSTRALIA
Andes

Cape of
Good Hope

Tasmania
Cape Horn New
Tierra del Fuego Zealand
Figure 22.5


Darwin’s Focus on Adaptation
• As 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


• From studies made years after Darwin’s
voyage
– Biologists have concluded that this is indeed
what happened to the Galápagos finches

(a) Cactus eater. The long, (c) Seed eater. The large ground
sharp beak of the cactus finch (Geospiza magnirostris)
ground finch (Geospiza has a large beak adapted for
scandens) helps it tear cracking seeds that fall from
and eat cactus flowers plants to the ground.
and pulp.

Figure 22.6a–c (b) Insect eater. The green warbler
finch (Certhidea olivacea) uses its
narrow, pointed beak to grasp insects.

• In 1844, Darwin wrote a long essay on the
origin of species and natural selection
– But he was reluctant to introduce his theory
publicly, anticipating the uproar it would cause

• In June 1858 Darwin received a manuscript
from Alfred Russell Wallace
– Who had developed a theory of natural
selection similar to Darwin’s

• Darwin quickly finished The Origin of Species
– And published it the next year

The Origin of Species
• Darwin developed two main ideas
– Evolution explains life’s unity and diversity

– Natural selection is a cause of adaptive
evolution


Descent with Modification
• 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


• In the Darwinian view, the history of life is like a tree

– With multiple branchings from a common trunk
to the tips of the youngest twigs that represent
the diversity of living organisms
Sirenia Elephas Loxodonta Loxodonta
Hyracoidea (Manatees
maximus africana cyclotis
Years ago

(Hyraxes) and relatives) (Africa)
(Asia) (Africa)

Mammuthus
Stegodon
Mammut
Deinotherium

Platybelodon
Millions of years ago

Barytherium
Moeritherium

Figure 22.7

Natural Selection and Adaptation
• Evolutionary biologist Ernst Mayr
– Has dissected the logic of Darwin’s theory into
three inferences based on five observations


• Observation #1: For any species, population
sizes would increase exponentially
– If all individuals that are born reproduced
successfully

Figure 22.8


• Observation #2: Nonetheless, populations tend
to be stable in size
– Except for seasonal fluctuations

• Observation #3: Resources are limited

• Inference #1: Production of more individuals
than the environment can support
– Leads to a struggle for existence among
individuals of a population, with only a fraction
of their offspring surviving


• Observation #4: Members of a population vary
extensively in their characteristics
– No two individuals are exactly alike

Figure 22.9


• Observation #5: Much of this variation is
heritable
• Inference #2: Survival depends in part on
inherited traits
– Individuals whose inherited traits give them a
high probability of surviving and reproducing
are likely to leave more offspring than other
individuals


• Inference #3: This unequal ability of individuals
to survive and reproduce
– Will lead to a gradual change in a population,
with favorable characteristics accumulating
over generations


Artificial Selection
• In the process of artificial selection
– Humans have modified other species over
many generations by selecting and breeding
individuals that possess desired traits
Terminal Lateral
bud buds

Cabbage Brussels sprouts

Flower Leaves
cluster

Cauliflower Kale

Flower
Stem
and
stems
Broccoli Wild mustard Kohlrabi

Figure 22.10

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


• Natural selection can produce an increase over time

– In the adaptation of organisms to their
environment
(a) A flower mantid
in Malaysia

(b) A stick mantid
in Africa

Figure 22.11

• If an environment changes over time
– Natural selection may result in adaptation to
these new conditions


• 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
• Two examples
– Provide evidence for natural selection


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

Experimental
transplant of
Predator: Killifish; preys guppies
mainly on small 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.
Weight of guppies
at maturity (mg)

at maturity (days)
Control Population: Guppies

Age of guppies
185.6
161.5 85.7 92.3
from pools with pike-cichlids
58.2 as predators
48.5
67.5 76.1
Experimental Population:
Guppies transplanted to
Males Females Males Females pools with killifish as
predators

CONCLUSION 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


• Researchers have developed numerous drugs
to combat HIV
– But using these medications selects for
viruses resistant to the drugs
Patient
Percent of HIV resistant to 3TC

No. 1
Patient No. 2

Patient No. 3

Weeks

Figure 22.13

• The ability of bacteria and viruses to evolve
rapidly
– Poses a challenge to our society


Homology, Biogeography, and the Fossil Record
• Evolutionary theory
– Provides a cohesive explanation for many
kinds of observations


Homology
• Homology
– Is similarity resulting from common ancestry


Anatomical Homologies
• Homologous structures between organisms
– Are anatomical resemblances that represent
variations on a structural theme that was
present in a common ancestor

Human Cat Whale Bat
Figure 22.14

• Comparative embryology
– Reveals additional anatomical homologies not
visible in adult organisms

Pharyngeal
pouches

Post-anal
tail

Chick embryo Human embryo
Figure 22.15


• Vestigial organs
– Are some of the most intriguing homologous
structures
– Are remnants of structures that served
important functions in the organism’s
ancestors


Molecular Homologies
• Biologists also observe homologies among
organisms at the molecular level
– Such as genes that are shared among
organisms inherited from a common ancestor


Homologies and the Tree of Life
• The Darwinian concept of an evolutionary tree
of life
– Can explain the homologies that researchers
have observed


• Anatomical resemblances among species
– Are generally reflected in their molecules, their
genes, and their gene products
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Species
Human Hemoglobin Polypeptide

Human 100%

Rhesus monkey 95%

Mouse 87%

Chicken 69%

Frog 54%

14%
Figure 22.16 Lamprey


Biogeography
• Darwin’s observations of the geographic
distribution of species, biogeography
– Formed an important part of his theory of
evolution


• Some similar mammals that have adapted to
similar environments
– Have evolved independently from different ancestors

NORTH
AMERICA
Sugar
glider

AUSTRALIA

Flying
squirrel

Figure 22.17

The Fossil Record
• The succession of forms observed in the fossil
record
– Is consistent with other inferences about the
major branches of descent in the tree of life


• The Darwinian view of life
– Predicts that evolutionary transitions should
leave signs in the fossil record

• Paleontologists
– Have discovered fossils of many such
transitional forms

Figure 22.18

What Is Theoretical about the Darwinian View of Life?
• In science, a theory
– Accounts for many observations and data and
attempts to explain and integrate a great
variety of phenomena


• Darwin’s theory of evolution by natural
selection
– Integrates diverse areas of biological study
and stimulates many new research questions


Darwin's revolutionary theory of evolution by natural selection

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (20)

Similar to Darwin's revolutionary theory of evolution by natural selection

Similar to Darwin's revolutionary theory of evolution by natural selection (20)

Darwin's revolutionary theory of evolution by natural selection