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Lecture topics
Evolution defined
Darwin’s influences
Darwin’s evidence
Darwin’s argument
“The Modern Synthesis”
Modern evidence
Key Concepts
Populations and species evolve, meaning that
their heritable characteristics change through
time. Evolution is change in allele frequencies
over time.
Natural selection occurs when individuals with
certain alleles produce the most surviving
offspring in a population. An adaptation is a
genetically based trait that increases an
individual’s ability to produce offspring in a
particular environment.
Key Concepts
Evolution by natural selection is not
progressive, and it does not change the
characteristics of the individuals that are
selected―it changes only the characteristics
of the population. Animals do not do things
for the good of the species, and not all traits
are adaptive. All adaptations are constrained
by trade-offs and genetic and historical
factors.
What is evolution?
• Microevolution: changes in allele frequencies in a
population across generations
– An ecological population is a group of individuals of the
same species living in a defined geographical area
– A genetic population or gene pool is the pooled set of
alleles from all the members of that ecological population.
• It represents the set of alleles that can likely combine in
a group isolated from other such groups by limited
migration
• Macroevolution: major evolutionary changes
involving the origin of new species
Charles Darwin
• Darwin was not the first to
think of the idea of
evolution.
• His contribution is the
mechanism of evolution
by natural selection
published in The Origin of
Species
Voyage of the Beagle 1831-1836
• Darwin was lucky!
• Explored coasts of South
America, Australia and
Galapagos Islands
On the Origin of
“On The Origin of Species”
• Darwin developed his ideas
for 20 years after Beagle
voyage
• Alfred Russel Wallace
(The Malay Archipelago)
nearly “scooped” him
• Presented “joint papers” to
Linnaean Society (1858)
• “Origin” (1859) is “only an
abstract”
Darwin Synthesized Ideas From Many Sources
• Jean Baptist Chevalier de
Lamarck 1744-1829
(Philosophie Zoologique)
• Suggested species
change and adapt
• His mechanism –
inheritance of acquired
characteristics – was
wrong, but…
Fig. 20.1.a
Fig. 20.1.b
Other evidence supported idea of mutability
Fruit - eating
seed - eating
grub/worm eating
• Darwin’s own observations
– Galapagos finches (Geospizinae)
– Changes in fossils and similarity between
living and extinct forms
Fig. 21.7
Domestication/
Artificial selection
Darwin Synthesized Ideas From Many Sources
Charles Lyell: (1797-1875)
Geologist
(Principles of Geology)
• Uniformitarianism
• Gradualism (replaced
catastophism)
• Geological column
• Ideas supported by other
evidence
– Fossils, earth movements
Darwin Synthesized Ideas From Many Sources
Charles Lyell: (1797-1875)
Geologist
(Principles of Geology)
Youngest
• Uniformitarianism
• Gradualism (replaced
catastophism)
• Geological column
• Ideas supported by other
evidence
– Fossils, earth movements
Oldest
Darwin Synthesized Ideas From Many Sources
Rev. Thomas Malthus:
1766-1834 Economist
(Essay on the Principle of
Population)
• Food production linear
• Population growth
exponential
Surplus population, which
must starve
Food production or
Food needs (Population)
Malthus' Idea
18
16
Food
14
12
Population
10
8
6
4
2
0
0
10
20
Tim e
.
3
Darwin Synthesized Ideas From Many Sources
Rev. Thomas Malthus: Economist
(Essay on the Principle of Population)
• Food production linear
• Population growth exponential
Surplus population, which must starve
• Darwin argued that “A grain in the balance
will determine which individual shall live
and which shall die,—which variety or
species shall increase in number, and which
shall decrease, or finally become extinct.”
Darwin Synthesized Ideas From Many Sources
Carolus Linnaeus:
1707-1778 Father of
taxonomy (Systema
Naturae)
• Classified organisms in
a nested hierarchy i.e.,
groups within groups
• To Darwin, suggested
branching pattern of
descent
Darwin Synthesized Ideas From Many Sources
Biogeography: patterns of geographical
distributions of living things
• Regional similarity among species
– New world vs. old world warblers
– Island & mainland spp.
– Fossil & extant spp.
Darwin Synthesized Ideas From Many Sources
Comparative Anatomy
• Homology – shared structure based on
shared anatomical design (shared
because derived from common ancestor)
• e.g., Wing of bat, human hand, cat’s paw,
whale’s flipper
Darwin Synthesized Ideas From Many Sources
Comparative Anatomy
• Homology – shared structure based on
shared anatomical design (shared
because derived from common ancestor)
• e.g., Pea tendril and cactus spine both
modified leaves
Darwin Synthesized Ideas From Many Sources
Comparative Anatomy
• Homology – shared structure based on
shared anatomical design (shared
because derived from common ancestor)
– e.g., Wing of bat, human hand, cat’s paw,
whale’s flipper
– e.g., Pea tendril and cactus spine both
modified leaves
• Contrast homology with homoplasy
(analogy)
Convergent evolution and
homoplasy
• Analogous (homoplastic) features:
similar in structure because serve a
similar function, not because they are
derived from a common ancestor
• Result from convergent evolution
• e.g., Barberry and hawthorn thorns
Convergent evolution and homoplasy
• Analogous (homoplastic) features: similar
in structure because serve a similar
function, not because they are derived
from a common ancestor
• Result from convergent evolution
• e.g., fusiform shape of shark, tuna,
ichthyosaur, and porpoise
Convergent evolution and homoplasy
• E.g., Similarities between placental and
marsupial mammals
Convergent evolution and
homoplasy
• Homology and homoplasy are
relative terms: Bat, bird, and
pterosaur wings are homologous as
forelimbs, but homoplastic as
wings, since each derived from
forelimb of different ancestor
Darwin Synthesized Ideas From Many Sources
Comparative Anatomy
• Vestigial structures – remnants of
previously functional organs
–e.g., human tail and appendix
–e.g., pythons’ and boas’ spurs
Darwin Synthesized Ideas From Many Sources
Comparative Anatomy
• Embryology – Similarity greatest
between close relatives.
• e.g., most vertebrates, gradually
become distinguishable as different
classes, orders…as development
proceeds
•Problem: Early drawings by Haeckel as
evidence that “ontogeny recapitulates
phylogeny” appear too similar
•Presumably
fudged to
enhance
similarity
• The truth revealed?
You decide…
More “honest”
images
• Still, general
pattern of greater
similarity among
closer relatives
Darwin’s Four Postulates
1. Individuals in a population vary in their traits.
PHENOTYPES.
2. Some of these differences are heritable; they are passed on to
offspring.
3. In each generation, many more offspring are produced than can
survive; of these, only some will survive long enough to
reproduce, and some
will
produce
than offspring
others.
among
these,
somemore
will offspring
produce more
than others.
4. Individuals with certain heritable traits are more likely to survive
reproduce.
when individuals
with
4. and
Individuals
withNatural
certainselection
heritableoccurs
PHENOTYPES
are more
certain
produce
more offspring
thanselection
do individuals
likely totraits
survive
and reproduce.
Natural
occurs without
when
those
traits. with certain PHENOTYPES produce more offspring
individuals
than do individuals with other PHENOTYPES.
© 2011 Pearson Education, Inc.
Darwin’s Postulates: The Logic of
the Argument for Natural Selection
1. Individuals vary and this variation is
heritable
2. There is surplus production
3. There is competition among variants for
limited resources or to avoid predators
4. Some variants are better suited to leave
offspring than others
•
Variants best suited to the environment will
increase, while those least suited will decrease
Andy’s Version
• If phenotypes vary within a population
• And that variation is heritable (i.e., has a
genetic component – not just environmental)
• And there is a relationship between between
phenotype and reproductive success
• Then genotypes that produce more successful
phenotypes will increase relative to genotypes
that produce less successful phenotypes
• Note: there is no need for surplus production for
this to work (though that would accelerate it)!
Darwin’s Dangerous Idea
• Darwin argued that all animals must
have descended from a common
ancestor.
• He then noted the many underlying
similarities between plants and
animals, then followed this logic to a
natural conclusion.
Darwin’s Dangerous Idea
“Therefore I should infer from
analogy that probably all the
organic beings which have ever
lived on this earth have descended
from some one primordial form,
into which life was first breathed.”
Evolution since Darwin
• Natural selection widely accepted based on
logic, even though heredity not understood
– Mendel a contemporary to Darwin, but his
work not recognized until discovered by
Correns, DeVries and von Tschermak
• Discovery of genetics and mutation led to
decline in support for Darwinism!
– Mutations thought main driver of evolution
The Modern Synthesis
• Mathematical population geneticists
reconciled natural selection with genetics
• Sewall Wright, Ronald A. Fisher, J.B.S.
Haldane, Theodosius Dobzhansky,
Ernst Mayr, George Gaylord Simpson
• Neo-Darwinism generally accepted since
the 1930s
Molecular Evidence
• All organisms use same genetic code
(with some minor variations)
• Similarity of code reflects pattern of
descent
–More similar-looking species share
more of their DNA
• Similarity of proteins also
Molecular Clocks
• DNA undergoes relatively steady rates of
mutation over time
• Changes accumulate over time.
Accumulated difference between two species
indicates time since shared ancestor
• Allows biologists to construct molecular
clocks based on the rates of change in
homologous DNA
• This can aid in the dating of branching points
in the evolutionary record
Transitional
Fossils
• Darwin suggested whales may
have originated from terrestrial
mammal (e.g., swimming bear)
• New fossils (Phil Gingerich, Hans
Thewissen) suggest whales
derived from mesonychid ruminants
that moved to the sea
• Ambulocetus otter-like (~50 mybp)
• Rodhocetus (45-50 mybp)has fluke
and vertebrae for vertical flapping
• Basilosaurus (40 mybp) nearly
modern structure with reduced hind
limbs
• Vestigial hind limbs still present in
modern whales
Fig. 21.17
Supported by molecular data
• Molecular and
anatomical
analyses suggest a
close relationship
between whales
and ruminants.
• Hippos seem to be
whales’ closest
living relatives
Sometimes new finds
fall right in place!
• Some transitional fishes so
intermediate that some authors
classified as fish, others as
amphibians based on partial
fossils
• Tiktaalik just discovered about 6
years ago!
• Right age and morphology to fit
amid other transitional fish
Direct Observation of Evolution
• H. B. D. Kettlewell – industrial melanism in
the peppered moth, Biston betularia
Direct Observation of Evolution
• Resistance to insecticides and antibiotics
Three bad habits foster evolution of
antibiotic resistance
1. Overprescription of antibiotics
2. Not finishing course of antibiotics
3. Routine use of antibiotics in
livestock
Field Experiment on Evolution
• David Reznick and John Endler –
Venezuelan and Trinidadian guppies
• Observation: Size and color vary above vs.
below waterfalls.
So do the predators present.
– Crenicichla large, can eat all size classes
– Rivulus smaller, can not eat adult guppies
Fig. 20.17
Guppies
larger and
more
colorful
above
waterfalls
Reznick and Endler, cont’d
• Hypothesis: size-selective predation
– Below falls: Large predator (Crenicichla)
eats all sizes, so selection favors early
reproduction at small size
– Above falls: Small predator (Rivulus)
eats juveniles, but cannot eat adults, so
selection favors delaying reproduction
and reaching larger size
• Experiment: move fish from below to
above falls
Field Data
• After only 11 years above
falls, collected guppies
from above and below
falls
• Fish reared in a constant
lab environment for one
generation to control for
environmental effects
• Change is Evolution!
Fig. 20.18
Lab
experiment:
rear fish for
10
generations
alone and
with each
predator
•Population exposed to Crenicichla
became less colorful
Lecture topics
Evolution defined
Early ideas on evolution
Darwin’s influences
Darwin’s evidence
Darwin’s argument
Darwinism’s near death and resurrection
“The Modern Synthesis”
Modern evidence