Darwin & Theory of Evolution
by Natural Selection
Chapter 22
Evolution- Just a Theory?
• Theory vs. Law vs. Dogma
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Theory – explain
Laws describe
Dogma is not tested – beliefs
Science is limited to things we can
measure, test.
• Hypothesis – is an “educated” guess to
explain a problem,
Scientific Method
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Problem, observation
Background information, literature search
Hypothesis based on previous work
Experiment to test hypothesis
Analyze results
If hypothesis supported – publish a paper.
Darwin’s Theory
• Populations have inherent variation among
individuals.
• These traits are heritable
• Resources in the environment are limited
• Populations have a greater fertility than their
environment can sustain.
• Populations would grow exponentially, but most
remain stable in size.
A population of Liguus fascitus
Variation in shell coloration patterns
Fig. 22-10
Darwin’s Theory continued:
• There is a struggle to survive among the
offspring called Natural Selection.
• The survivors are better fit
• Fitness is the ability to have more offspring
(frequency of genes in the genepool).
Natural Selection
• “struggle “ or competition does not have to
be a fight to death
• may just be as simple as a seed
germinating earlier and getting established
first. It produces 120 seeds. A later
germinating plant makes only 50 seeds.
• “Fitness” is the success rate of the
offspring in future generations.
Fig. 22-7
Fig. 22-19
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
Some Evidence for Evolution
• Microevolution- antibiotic, pesticide resistance
– Artificial selection
• Fossil record
• Biochemical comparisons
– Protein sequences
– DNA, gene comparisons
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Morphological comparisons
Embryology
Biogeography
Genetically modified organisms
Fig. CO 13
All made by Artificial
Selection from wild mustard
Artificial Selection: human designed breeding of plants and animals for desired
traits by selecting which individuals get to reproduce.
Fig. 22-9
Terminal
bud
Lateral
buds
Cabbage
Brussels sprouts
Flower
clusters
Leaves
Kale
Cauliflower
Stem
Wild mustard
Flowers
and stems
Broccoli
Kohlrabi
Fig. 25-18
Close North American relative,
the tarweed Carlquistia muirii
Dubautia laxa
KAUAI
5.1
million
years
MOLOKAI
OAHU
3.7 LANAI
million
years
1.3
MAUI million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Fossils
• Give us real dates
• Show us what the “intermediate” features
looked like
• “Missing Links” the intermediate species
along lineages
– e.g.. From apes to humans
• Very limited, chances of a species getting
fossilized are low.
Fig. 22-3
Layers of deposited
sediment
Younger stratum
with more recent
fossils
Older stratum
with older fossils
Missing Links
Fig. 22-16
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)
Fig. 13.4
Fig. 22-8
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
Fig. 22-8a
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
Fig. 13.3
Fig. 22-15
0
Fossil
Evidence
of Evolution
in a group of
Trilobites
over time
2
4
4
6
4 Bristolia insolens
8
3 Bristolia bristolensis
10
12
3
2 Bristolia harringtoni
14
16
Location
and angle of
head spines
18 1 Bristolia mohavensis
3
2
1
Latham Shale dig site, San
Bernardino County, California
Fig. 22-15c
0
2
4
3
Depth (meters)
4
6
4
Bristolia insolens
8
3
Bristolia bristolensis
10
Vestigial Structures
• Come from an ancestral species
• No longer serve an function
• Are neutral traits, not harmful, and thus not
“selected against” in origins of new
species
– Appendix
– Hip bones in Pythons, Whales
– Ear muscles in humans
backbone
pelvic girdle
coccyx (bones
where many
other mammals
have a tail)
thighbone
attached to
pelvic girdle
small bone
attached to
pelvic girdle
Molecular Comparisons
• Counts mutations to an important gene
• “Conserved” genes mutate slowly, used to
show distant relationships
• Can compare any living species, or fossil
tissues that still have DNA
• Show how closely they are related
• Doesn’t show what intermediate species
looked like
Fig. 13.5
Molecular clocks
• Useful comparisons of any living species
• Uses date from fossil for when species
lineages separated
• Compares mutations to common gene
between these species to show a rate of
mutation in a gene
• Can make an estimate for species with
that gene, that do not have a fossil record
• Gives an estimated date
Fig. 13.6
Embryology
• Animals only, especially the vertebrates
• The more closely related two species are
the more similar their embryo will be for a
longer period of development
Fig. 22-18
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
Comparative embryology
Comparative embryology
Structures
• Homologous structures– Show common ancestry
– Derived from a common ancestral structure
– May have specialized into different functions
Homologous Bones in
Mammals
Fig. 22-17
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Human
Cat
Whale
Bat
Analogous Features
• Have same functions ( by convergence)
• Do not have a common ancestry
• Are not derived from the same ancestral feature
Butterfly and Bird
• No bones in butterfly, not
from common ancestor
• Structures not related
Convergence
• Not closely related
• Look similar due to adapting to similar
habitat
Fig. 13.9b
Rate of evolution
• Gradualism- slow and constant changes
build up over time to make new species.
• Punctuated equilibrium there are relatively
brief ( in geologic time scale) periods with
rapid change, followed by long periods
with little change in species.
– Follow periods of climate change and mass
extinctions
Fig. 13.2
Charles Darwin
Putting Darwin in the context
of his time
Important people
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Linnaeus
Lamarck
Cuvier
Malthus
Lyell
Wallace
Natural Theology
• Belief that studying nature revealed divine
knowledge – arguments to prove the existence
of God – without supernatural revelation.
– Paley’s watchmaker argument
– Intelligent design arguments of today
Used along with Christian Beliefs based on a literal
view of the Genesis Story:
• Earth 6,000 yrs old
• No new species
• No physical changes (valleys, mountains)
• Study, categorizing nature to reveal a divine
plan.
Linnaeus
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Studying biology to reveal a divine plan
Developed modern taxonomy
Made Binomials: Homo sapiens
Based groupings on morphology
Did not believe in evolution,
Taxonomy data would later provide some
of best evidence
His Purpose:
• The Earth's creation is the glory of God, as
seen from the works of Nature by Man
alone. The study of nature would reveal
the Divine Order of God's creation, and it
was the naturalist's task to construct a
"natural classification" that would reveal
this Order in the universe.
• He liked to say
' Deus creavit,
Linnaeus
disposuit, '
Latin for, "God
created,
Linnaeus
organized".
Other accomplishments:
• Reversed Celsius’ thermometer – from
100 – melting and 0 boiling to today’s
• 0 – freezing, 100 boiling.
Still very early science:
• Also named (as real) in his taxonomy various
mythological animals; including the troglodyte,
satyr, hydra, and phoenix
• Included other human species from legends:
– Homo ferus: four footed, mute & hairy
– Juvenis lupinus - wolf boys
• Still use his method of classification into
hierarchies and the binomial, not his actual
taxonomy.
• He did classify humans as animals, and then as
primates. Controversial for the time.
Cuvier
• Developed Paleontology
– the study of fossils
• deeper the strata (layers) more dissimilar
to current organisms
• Didn’t believe in evolution
• Thought strata relate to catastrophic
events ( Noah’s flood etc.) and
replacement by migration
Lamarck
• Got the genetics wrong
• Stressed acquired traits-(wrong)
– Giraffes stretched their necks
– Babies had longer necks
• But- said species evolved to be better
suited to environment – right!
Fig. 13.1
Malthus
• British economist studied Paris after the
revolution
• Limited resources
• Excess population growth
• Struggle to survive,
• competition among individuals
• Survival of the richest
Lyell
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British geologist.
Following Hutton’s work
Earth is old
Valleys formed by erosion
Mountains by uplifting
Slow processes over long periods of time
Voyage of the Beagle
Galapagos Finches
• Specialization to different feeding sources
may have diversified the species.
Darwin
Wolf
Pinta
Genovesa
Marchena
Santiago
Bartolomé
Fernandia
Rabida
Pinzon
Baltra
Santa Cruz
Santa Fe
San Cristobal
Isabela
Tortuga
Floreana
Española
Fig. 22-6
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
Fig. 22-12
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Fig. 22-UN1
Observations
Individuals in a population
vary in their heritable
characteristics.
Organisms produce more
offspring than the
environment can support.
Inferences
Individuals that are well suited
to their environment tend to leave
more offspring than other individuals
and
Over time, favorable traits
accumulate in the population.
Fig. 22-UN2
Fig. 22-UN3
Evidence that Made Darwin think..
• The variation among organisms in a population
• Biogeography – where species are found around
the globe
• Fossil record
• Comparative morphology – Linnaeus's
classification
• Artificial Selection
• Geology and the age of the earth
• Malthus and economic theory
• Lamarck’s theory and adaptations
Darwin and
Human Evolution
• Published “Descent
of Man” in 1871
• Wasn’t first to
hypothesis our
relation to apes
• caused more popular
criticism of his
general theory
• “There is grandeur in this view of life, with
its several powers, having been originally
breathed into a few forms or into one; and
that, whilst this planet has gone cycling on
according to the fixed law of gravity, from
so simple a beginning endless forms most
beautiful and most wonderful have been,
and are being, evolved.”