Download descent with modification

DESCENT WITH
MODIFICATION:
A DARWINIAN VIEW OF LIFE
Chapter 22
• Darwin noted that current species are
descendants of ancestral species
• Evolution can be defined by Darwin’s phrase
descent with modification
• Evolution can be viewed as both a pattern and
a process
Fig. 22-1
Fig. 22-2
Concept 22.1: The Darwinian revolution challenged
traditional views of a young Earth inhabited by
unchanging species
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
American Revolution
French Revolution
U.S. Civil War
1800
1900
1750
1850
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his hypothesis of evolution.
1830 Lyell publishes Principles of Geology.
1831–1836 Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks.
1844 Darwin writes essay on descent with modification.
1858 Wallace sends his hypothesis to Darwin.
1859 The Origin of Species is published.
Scala Naturae and Classification of Species
• The Greek philosopher Aristotle viewed
species as fixed and arranged them on a scala
naturae
• The Old Testament 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
• Linnaeus was the founder of taxonomy, the
branch of biology concerned with classifying
organisms
Ideas About Change over Time
• 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
Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Older stratum
with older fossils
• Paleontology, the study of fossils, was largely
developed by French scientist Georges Cuvier
• Cuvier advocated catastrophism, speculating
that each boundary between strata represents
a catastrophe
• Geologists James Hutton and Charles Lyell
perceived that changes in Earth’s surface can
result from slow continuous actions still
operating today
• Lyell’s principle of uniformitarianism states
that the mechanisms of change are constant
over time
• This view strongly influenced Darwin’s thinking
Lamarck’s Hypothesis of Evolution
• Lamarck hypothesized that species evolve
through use and disuse of body parts and the
inheritance of acquired characteristics
• The mechanisms he proposed are unsupported
by evidence
Concept 22.2: Descent with modification by natural
selection explains the adaptations of organisms and
the unity and diversity of life
• As the 19th century dawned, it was generally
believed that species had remained unchanged
since their creation
• However, a few doubts about the permanence
of species were beginning to arise
Fig. 22-5
Darwin’s Research
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Equator
Marchena
Santiago
Fernandina
Isabela
Daphne
Islands
Pinzón
Santa
Santa
Cruz
Fe
Florenza
SOUTH
AMERICA
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Cape of
Good Hope
Tasmania
Española
Cape Horn
Tierra del Fuego
New
Zealand
Darwin’s Focus on Adaptation
• In reassessing his observations, Darwin
perceived 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
Figure 22.6 Beak variation in Galápagos finches
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
• In 1844, Darwin wrote an essay on the origin of
species and natural selection but did not
introduce his theory publicly, anticipating an
uproar
• 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:
– Descent with modification explains life’s unity
and diversity
– Natural selection is a cause of adaptive
evolution
Descent with Modification
• Darwin never used the word evolution in the first edition of
The Origin of Species
• The phrase descent with modification summarized
Darwin’s perception of the unity of life
• The phrase refers to the view 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
branches representing life’s diversity
• Darwin’s theory meshed well with the hierarchy of
Linnaeus
Fig. 22-8
Descent with
Modification
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Platybelodon
Stegodon
Mammuthus
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa)
34
24
Millions of years ago
5.5
2 104 0
Years ago
Artificial Selection, Natural Selection, and
Adaptation
• Darwin noted that humans have modified other
species by selecting and breeding individuals
with desired traits, a process called artificial
selection
• Darwin then described four observations of
nature and from these drew two inferences
• Observation #1: Members of a population often
vary greatly in their traits
• Observation #2: Traits are inherited from
parents to offspring
• Observation #3: All species are capable of
producing more offspring than the environment
can support
• Observation #4: Owing to lack of food or other
resources, many of these offspring do not
survive
Fig. 22-9 Artificial Selection
Fig. 22-11
Overproduction of Offspring
Terminal
bud Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Spore
cloud
Leaves
Kale
Cauliflower
Stem
Fig. 22-10 Variation in a Population
Wild mustard
Broccoli
Flowers
and stems
Kohlrabi
• Inference #1: Individuals whose inherited traits
give them a higher probability of surviving and
reproducing in a given environment tend to
leave more offspring than other individuals
• Inference #2: This unequal ability of individuals
to survive and reproduce will lead to the
accumulation of favorable traits in the
population over generations
• Darwin was influenced by Thomas Malthus
who noted the potential for human population
to increase faster than food supplies and other
resources
• If some heritable traits are advantageous,
these will accumulate in the population, and
this will increase the frequency of individuals
with adaptations
• This process explains the match between
organisms and their environment
Natural Selection: A Summary
• Individuals with certain heritable characteristics
survive and reproduce at a higher rate than
other individuals
• Natural selection increases the adaptation of
organisms to their environment over time
• If an environment changes over time, natural
selection may result in adaptation to these new
conditions and may give rise to new species
Fig. 22-12 Camouflage as an example of evolutionary adaptation
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
• Note that individuals do not evolve;
populations evolve over time
• Natural selection can only increase or
decrease heritable traits in a population
• Adaptations vary with different environments
Concept 22.3: Evolution is supported by an
overwhelming amount of scientific evidence
• New discoveries continue to fill the gaps
identified by Darwin in The Origin of Species
Direct Observations of Evolutionary Change
• Two examples provide evidence for natural
selection: the effect of differential predation on
guppy populations and the evolution of drugresistant HIV
Predation and Coloration in Guppies : Scientific
Inquiry
• John Endler has studied the effects of
predators on wild guppy populations
• Brightly colored males are more attractive to
females
• However, brightly colored males are more
vulnerable to predation
• Guppy populations in pools with fewer
predators had more brightly colored males
Fig. 22-13 Can predation result in natural selection for color patterns in guppies?
EXPERIMENT
Predator: Killifish; preys
mainly on juvenile
guppies (which do not
express the color genes)
Experimental
transplant of
guppies
Pools with
killifish,
but no
guppies prior
to transplant
Guppies: Adult males have
brighter colors than those
in “pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on adult guppies
Guppies: Adult males are more drab in color
than those in “killifish pools”
RESULTS
As predicted, over time the population
became more brightly colored
12
Number of
colored spots
12
10
8
6
4
2
0
Source
population
Transplanted
population
10
8
6
4
2
0
Source
population
Transplanted
population
The Evolution of Drug-Resistant HIV
• The use of drugs to combat HIV selects for
viruses resistant to these drugs
• HIV uses the enzyme reverse transcriptase to
make a DNA version of its own RNA genome
• The drug 3TC is designed to interfere and
cause errors in the manufacture of DNA from
the virus
• Some individual HIV viruses have a variation
that allows them to produce DNA without errors
• These viruses have a greater reproductive
success and increase in number relative to the
susceptible viruses
• The population of HIV viruses has therefore
developed resistance to 3TC
• The ability of bacteria and viruses to evolve
rapidly poses a challenge to our society
• Natural selection does not create new traits,
but edits or selects for traits already
present in the population
• The local environment determines which traits
will be selected for or selected against in any
specific population
The Fossil Record
• The fossil record provides evidence of the
extinction of species, the origin of new groups,
and changes within groups over time
Fig. 22-15 Fossil
evidence of
evolution in a
group of trilobites
0
2
4
4
6
4 Bristolia insolens
8
3 Bristolia bristolensis
10
12
3
2 Bristolia harringtoni
14
16
18 1 Bristolia mohavensis
3
2
1
Latham Shale dig site, San
Bernardino County, California
• 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
Fig. 22-16 The
transition to life in
the sea
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)
Homology
• Homology is similarity resulting from common
ancestry
Anatomical and Molecular Homologies
• Homologous structures are anatomical
resemblances that represent variations on a
structural theme present in a common ancestor
Fig. 22-17 Mammalian forelimbs: homologous structures
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
• Comparative embryology reveals anatomical
homologies not visible in adult organisms
Fig. 22-18 Anatomical similarities in vertebrate embryos
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
• Vestigial structures are remnants of features
that served important functions in the
organism’s ancestors
• Examples of homologies at the molecular level
are genes shared among organisms inherited
from a common ancestor
Homologies and “Tree Thinking”
• The Darwinian concept of an evolutionary
tree of life can explain homologies
• Evolutionary trees are hypotheses about the
relationships among different groups
• Evolutionary trees can be made using different
types of data, for example, anatomical and
DNA sequence data
Fig. 22-19 Tree thinking: information provided in an evolutionary tree
Branch point
(common ancestor)
Lungfishes
Amphibians
1
Mammals
2
Tetrapod limbs
Amnion
Lizards
and snakes
3
4
Homologous
characteristic
Crocodiles
Ostriches
6
Feathers
Hawks and
other birds
Birds
5
Convergent Evolution
• Convergent evolution is the evolution of
similar, or analogous, features in distantly
related groups
• Analogous traits arise when groups
independently adapt to similar environments in
similar ways
• Convergent evolution does not provide
information about ancestry
Fig. 22-20
Sugar
glider
NORTH
AMERICA
AUSTRALIA
Convergent
evolution
Flying
squirrel
Biogeography
• Darwin’s observations of biogeography, the
geographic distribution of species, formed an
important part of his theory of evolution
• Islands have many endemic species that are
often closely related to species on the nearest
mainland or island
• Earth’s continents were formerly united in a
single large continent called Pangaea, but
have since separated by continental drift
• An understanding of continent movement and
modern distribution of species allows us to
predict when and where different groups
evolved
What Is Theoretical About Darwin’s 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
• Ongoing research adds to our understanding of
evolution
You should now be able to:
1. Describe the contributions to evolutionary theory made by
Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace
2. Describe Lamarck’s theories, and explain why they have
been rejected
3. Explain what Darwin meant by “descent with modification”
4. List and explain Darwin’s four observations and two
inferences
5. Explain why an individual organism cannot evolve
6. Describe at least four lines of evidence for evolution by
natural selection