Download BIO41 CH22.pptx

11/19/14
BIOSC 041
Descent with Modification:
A Darwinian View of Life
Reference: Chapter 22
Outline
v  Paradigm
shifts in science
world
v  Fundamental tenets of evolution
v  Examples and evidence
v  Natural selection
v  Darwin’s
Paradigm shifts in science
v  A
new era of biology began in 1859 when Charles
Darwin published The Origin of Species
v  The
Origin of Species focused biologists’ attention
on the great diversity of organisms
v  The
Origin of Species arose from, and gave rise to,
one of the greatest paradigm shifts in science, one
that is still going on today
Paradigm Shift
v  Accepted
§ 
v  Accepted
§ 
view on a particular topic is challenged
Evidence accumulates from various sources
view shifts to new understanding
Seemingly overnight- but not really…
v  Examples
§ 
Geocentrism vs. Heliocentrism
§ 
Round vs. Flat Earth
§ 
Microbiology
§ 
Evolution
In Darwin’s Day…
In Darwin’s Day…
v  Age
v  Animals
§ 
§ 
of the Earth
5,000-6,000 years old
Earth was static
§  Oceans, mountains, etc. were fixed & did not change
except through divine action (e.g. Flood)
v  Earth
§ 
strata
§ 
§ 
& Plants
Created at the same time
Humans at the top of a “great chain of being”
v  Fossils
§ 
§ 
Believed to be the bones of demons/dragons OR
Strange mineral deposits that “grew” in the earth
Formed in place, within the earth
1
11/19/14
Paradigm Challenge
v  Evidence
was mounting that challenged traditional
views of a young Earth inhabited by unchanging
species
§ 
§ 
§ 
New views on geology
New views on religion and human societies
New views on biology
§  Earlier paradigm shift – microorganisms
§  Anatomical and developmental similarities between
very different groups of organisms
Ideas About Change over Time - Catastrophism
The study of fossils helped to lay the groundwork for
Darwin’s ideas
v  Paleontology, the study of fossils, was largely developed
by French scientist Georges Cuvier
v  Cuvier advocated catastrophism, speculating that each
boundary between strata represents a global, geologic
catastrophe (e.g. volcano, flood, etc.)
v 
Darwin’s Research – H.M.S. Beagle
Scala Naturae and Classification of Species
Greek philosopher Aristotle
viewed species as fixed and
arranged them on a scala
naturae (ladder of nature)
v  The Old Testament holds that
all species were individually
designed by God and
therefore perfect
v  Carolus Linnaeus interpreted
organismal adaptations as
evidence that the Creator had
designed each species for a
specific purpose
v 
Ideas About Change over Time - Uniformitarianism
v 
v 
v 
Darwin’s Research – H.M.S. Beagle
v 
Darwin served as naturalist during a
5-year around the world voyage on
the Beagle, where he collected
specimens of South American plants
and animals
v  Observed that fossils resembled
living species from the same
region, and living species
resembled other species from
nearby regions
v  Experienced an earthquake in Chile
and observed the uplift of rocks
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 gradual and constant over time
This view strongly influenced Darwin’s thinking
v 
v 
v 
Darwin was influenced by Lyell’s Principles of Geology and
thought that the earth was more than 6000 years old
His interest in geographic distribution of species was kindled
by a stop at the Galápagos Islands west of South America
He hypothesized that species from South America had
colonized the Galápagos and speciated on the islands
2
11/19/14
Figure 22.5
Figure 22.2
1809
Lamarck publishes
hypothesis of evolution.
1798
Darwin in 1840,
after his return
from the
voyage
Malthus publishes
“Essay on the Principle
of Population.”
HMS Beagle in port
Great
Britain
EUROPE
Genovesa
Isabela
0
20
40
Santa Santa
Cruz
Fe
Florenza
Kilometers
Equator
SOUTH
AMERICA
Equator
Daphne
Islands
Chile
PACIFIC
OCEAN
San
Cristobal
Española
Andes Mtns.
Marchena
Santiago
Pinzón
Fernandina
1830
Lyell publishes
Principles of Geology.
AFRICA
PACIFIC
OCEAN
Pinta
Brazil
Malay Archipelago
PACIFIC
OCEAN
1790
Charles Darwin
is born.
Cape of
Argentina Good Hope
Cape Horn
1831-36
1809
AUSTRALIA
Tasmania
New
Zealand
1858
Cuvier publishes extensive
studies of vertebrate fossils.
Hutton proposes
principle of
gradualism.
ATLANTIC
OCEAN
The
Galápagos
Islands
1812
1795
NORTH
AMERICA
Darwin travels around
the world on HMS
Beagle.
While studying species in
the Malay Archipelago,
Wallace (shown in 1848)
sends Darwin his hypothesis
of natural selection.
1859
1870
On the Origin of
Species is published.
1844
Darwin writes
essay on descent
with modification.
The Galápagos Islands
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
§  Coined the term “descent with
modification” to describe his
hypothesis for perceived
similarities and differences
between species
v  Modern evolutionary biologists have
confirmed Darwin’s hypothesis
regarding Galapagos finches and
iguanas (and other species as well)
v 
Natural Selection
v 
Darwin based his theory of natural selection on
two key observations:
1. 
2. 
Overproduction
Heritable variation among individuals
On The Origin of Species
v 
In 1844, Darwin wrote an essay on natural selection as
the mechanism of descent with modification, but did
not introduce his theory to a wide public audience
v 
Natural selection is a process in which individuals with
favorable inherited traits are more likely to survive and
reproduce
v 
In 1858, Darwin received a manuscript from Alfred
Russell Wallace, who had developed a theory of natural
selection similar to Darwin’s
v 
Darwin quickly finished The Origin of Species and
published it the next year
Observation 1: Overproduction
v  All
species tend to
produce excessive
numbers
§ 
§ 
Leads to a struggle for
existence
Now known as intraspecific
competition
v  Individuals
compete with
one another for food and
other resources
3
11/19/14
Observation 2: Individual variation
v  Variation
§ 
§ 
Darwin’s Big Leap
exists among individuals in a population
v 
Now known as phenotypic variation
Phenotype = physical trait expressed
v  Much
of this variation is heritable
v 
The result of natural selection is evolutionary
adaptation
Observation à Inference
§  Favorable traits that are heritable become more common
§  Unfavorable traits become more rare
Why?
§  Those individuals with traits best suited for the local
environment are more successful
§  Leave behind more offspring
§  Pass along more of their genes
Sources of Genetic Variation
Mutations and sexual recombination
§  Mutations are changes in the DNA of an organism
§  Sexual recombination shuffles alleles during meiosis
v  Sources of genetic variation occur at the level of the
individual
v  Natural selection may act at the level of the individual
v 
(b) A Trinidad tree
mantid that mimics
dead leaves
BUT
v 
(a) A flower mantid in Malaysia
(c) A leaf mantid in Costa Rica
Natural Selection does not act on the individual
v 
Evolution acts at the level of the population
Lamarck: believed that characteristics acquired by the
individual can be passed on to offspring
Natural Selection acts on populations (next lecture)
v 
Relies on heritable, phenotypic variation within a population
4
11/19/14
Descent from a common ancestor
Evolution is supported by an overwhelming amount
of scientific evidence
v  Darwin’s
1. 
§ 
§ 
§ 
ideas explained three broad observations:
The unity of life
The diversity of life
The match between organisms and their environment
v  Darwin
never used the word evolution in the first
edition of The Origin of Species
v  The phrase descent with modification summarized
Darwin’s perception of the unity of life
v  The phrase refers to the view that all organisms are
related through descent from an ancestor that lived
in the remote past
1. Evidence of Evolution – Fossil Record
Fossil Record
Comparative Anatomy
Comparative Embryology
Comparative Genomics
Biogeography
Artificial Selection
Evolution in Real Time
2. 
3. 
4. 
5. 
6. 
7. 
Figure 22.20
Other
even-toed
ungulates
The fossil record provides evidence of the extinction of
species, the origin of new groups, and changes within
groups over time
v  Fossils can document important transitions
§  For example, the transition from land to sea in the
ancestors of cetaceans
v 
Hippopotamuses
†Pakicetus
†Rodhocetus
Common
ancestor
of cetaceans
†Dorudon
Living
cetaceans
70
2. Evidence of Evolution – Homology & Comparative Anatomy
v 
Comparative anatomy
§ 
Comparison of body structure between species
§ 
Homology
§  Similarity in structures due to common ancestry
60
50
40
30
20
Millions of years ago
10
0
Key
Pelvis
Femur
Tibia
Foot
3. Evidence of Evolution – Comparative Embryology
v  Comparative
§ 
Embryology
the comparison of common structures that appear
during the development of different organisms
5
11/19/14
4. Evidence of Evolution – Genomic Similarities
v 
Evolutionary relationships among species
§ 
§ 
§ 
Leave markers in DNA and proteins
Can be determined by comparing genes and proteins of
different organisms
Another type of homology
Island Biogeography
v  Endemic
species are species that are not found
anywhere else in the world
v  Islands often have endemic species closely related
to species on the nearest mainland or island
v  Darwin explained that species on islands gave rise
to new species as they adapted to new
environments
7. Evidence of Evolution - Direct Observations
v 
Two examples provide evidence of natural selection
§ 
Natural selection of introduced plant species
§ 
Evolution of drug-resistant bacteria
5. Evidence of Evolution - Biogeography
v 
v 
v 
Biogeography is the geographic distribution of species
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 infer when and where
different groups evolved
6. Evidence of Evolution - Artificial Selection
v 
Humans have modified other species by selecting and
breeding individuals with desired traits from a common
ancestor
Natural Selection in Response to Introduced Plant
Species
Soapberry bugs use a “beak” to feed on seeds in fruits
In southern Florida soapberry bugs feed on native
balloon vine with larger fruit; they have longer beaks
v  In central Florida they feed on non-native goldenrain
tree with smaller fruit; they have shorter beaks
v  Correlation between fruit size and beak size has also
been observed in Louisiana, Oklahoma, and Australia
v 
v 
6
11/19/14
Soapberry Bug Evolution
Figure 22.13b
RESULTS
Beak
10
v  In
all cases, beak size has
evolved in populations
that feed on introduced
plants with fruits that are
smaller or larger than the
native fruits
v  These cases are examples
of evolution by natural
selection
v  In Florida this evolution in
beak size occurred in less
than 35 years
The Evolution of Drug-Resistant Bacteria
v 
v 
v 
v 
The bacterium Staphylococcus aureus is commonly found on
people
One strain, methicillin-resistant S. aureus (MRSA) is a
dangerous pathogen
S. aureus became resistant to penicillin in 1945, two years
after it was first widely used
S. aureus became resistant to methicillin in 1961, two years
after it was first widely used
A Different Cause of Resemblance: Convergent Evolution
v 
v 
v 
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
On native species,
southern Florida
8
Number of individuals
6
4
2
0
Museum-specimen average
10
On introduced species,
central Florida
8
6
4
2
0
6
7
8
9
Beak length (mm)
10
11
The Evolution of Drug-Resistant Bacteria
v 
v 
v 
v 
When exposed to methicillin, MRSA strains are more likely to
survive and reproduce than nonresistant S. aureus strains
MRSA strains are now resistant to many antibiotics
Antibiotic resistance is not a “learned” adaptation; bacteria
have short generation times and large population sizes,
which increase the rate at which they evolve
Drug-resistant bacteria are the result of spontaneous
mutation and natural selection
Natural Selection: A Summary
v 
v 
v 
v 
v 
v 
Individuals with heritable traits that are adaptive to the
current environment survive and reproduce at a higher rate
than other individuals
Over time natural selection increases the adaptation of a
population of organisms to their environment
If an environment changes over time, natural selection may
result in adaptation to these new conditions and may give
rise to new species
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
Evolution can be viewed as both a pattern and a process
7
11/19/14
What Is Theoretical About Darwin’s View of Life?
v 
v 
v 
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
§  Evolutionary biology is an active field- we don’t know
everything yet!
8