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Chapter 13: How
Populations Evolve
Evidence for Evolution
I.
Evolution & Darwin
II. Artificial Selection
III. Fossil Record
IV. Comparative Anatomy
V. Comparative embryology
VI. Genetic Analysis
VII. Biogeographical Evidence
VIII. Conclusions
I. Evolution & Darwin
Evolution = descent with modification
Æ Macroevolution = large changes
Æ Microevolution = small changes
Both rely on same mechanismsÆ
Primarily natural selection
Charles Darwin:
On the Origin of Species
(mid-1800’s)
“Nothing in biology makes sense except in the light of evolution”
--Theodosius Dobzhansky
I. Evolution & Darwin
I. Evolution & Darwin
• Traveled extensively
• Galapagos Islands—off the coast of Ecuador
• One area of focus: finches
North
America
Great
Britain
Europe
• Finches of the Galapagos
• 13 species
• Difference between them:
Asia
– Beak shape
ATLANTIC
OCEAN
PACIFIC
OCEAN
Africa
PACIFIC
OCEAN
Equator
The
Galápagos
Islands
Pinta
PACIFIC
OCEAN
South
America
Genovesa
Fernandina
0
0
Isabela Santa
Santa
San
Cruz Fe
Cristobal
40 km
Florenza Española
40 miles
Seed crackers
Cactus eaters
“Tool users”
Vampire
Australia
Andes
Marchena
Equator
Santiago
Daphne
Pinzón Islands
•
•
•
•
Cape of
Good Hope
Cape Horn
Tasmania
New
Zealand
Tierra del Fuego
While on the voyage of the HMS Beagle in the 1830s Charles
Darwin observed similarities between living and fossil organisms
and the diversity of life on the Galápagos Islands
I. Evolution & Darwin
Darwin proposed natural selection as the mechanism
of evolution
– Darwin observed that organisms
z
Produce more offspring than the environment can
support
z
Vary in many characteristics that can be inherited
– Darwin reasoned that natural selection
z
Results in favored traits being represented more and
more and unfavored ones less and less in ensuing
generations of organisms
– Darwin found convincing evidence for his ideas in the results
of artificial selection
z
The selective breeding of domesticated plants and
animals
• Darwin’s idea:
– One original species has adapted to different food
sources
Charles Darwin, 1859:
On the Origin of the Species
Charles Darwin proposed
Natural Selection as the
mechanism of evolution
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II. Artificial Selection
II. Artificial Selection (cont.)
CAN selection produce major evolutionary change?
Æ Darwin found convincing evidence for his ideas in the results of
artificial selection
Artificial selection:
• organisms may be modified by controlled breeding
• and change drastically in short time periods!
• 2 examples…
A) Plants
B) Mammals: Dogs
Change can happened
over a very short
geological period if the
selection pressure is
strong!
ÆBroccoli, brussel sprouts, kale,
cabbage, & cauliflower
Æ All artificially selected
from Brassica oleracea
III. The Fossil Record
Fossils: Preserved remains of ancient organisms
III. The Fossil Record
III. The Fossil Record
How to make a fossil:
Æ Burial in sediment
Æ Mineralization of organic
material
Æ Hardening of sediment
Organization of fossils:
a) Fossils are found in distinct layers
Darwin and his contemporaries saw and knew of fossils:
Æ Local fossils looked like local organisms
Æ Progressive changes in layers
• Fossil Record
– Remains or evidence of past life
– Dating fossils
• Relative dating – old layers under new
• Absolute dating – radioactive decay
– Fossilization chancy
• Right kind of organism, in right place
• Gaps unavoidable
– Many excellent series though
• Horses, titanotheres, whales, humans
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Organization of fossils:
a) Fossils are found in distinct layers
Fossil Record of Evolution:
Whale Evolution
b) Resemblance to modern forms of
life gradually increases with
younger fossils
Modern toothed whales
Ancient primitive organisms Æ
Several intermediary stages Æ
Modern forms
Rodhocetus kasrani
reduced hind limbs
could not walk;
swam with up-down motion
like modern whales
c) Many fossils are of species now
extinct
Ambulocetus natans
walked on land
…like sea lions
Pakicetus attocki
lived on land;
skull had whale
characteristics
Conclusions:
Æ Many different types of organisms
in the past (some extinct)
Æ Change in lineages over time
swam
by flexing & paddling
… like otters
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Facts – Geology and Fossils
• Fossils are found in sedimentary rocks
• Many fossils represent extinct organisms
• Oldest sedimentary rocks contain no fossils, or fossils of
extremely simple organisms
– Prokaryotes (stromatolites)
• Fossil prokaryotes appear prior to fossil eukaryotes
• Colonial eukaryotes appear prior to multicellular
eukaryotes (invertebrates and plants)
• Invertebrates appear prior to vertebrates
III. The Fossil Record: Evidence for Mass Extinctions
Diversity over the Last 600 Million Years
Number of families
III. The Fossil Record
800
600
400
200
0
600
500
Cambrian
(545-490)
400
Silurian
(438-408)
Ordovician
(490-438)
300
200
0
100
Carboniferous Triassic Cretaceous
(360-280)
(248-213) (144-65)
Devonian
(408-360)
Permian Jurassic
(280-248) (213-144)
Tertiary
(65-2)
Millions of years ago
–Fish, amphibians, reptiles, mammals, and birds appear in order
• Seedless vascular plants, seeds, gymnosperms, and
angiosperms appear in order
IV. Comparative Anatomy
Similar anatomy is found in organisms with greatly
divergent functions
Homologous structures
Æ structures that may have different appearances and functions,
yet all derived from a common ancestor
Vestigial structures are Evolutionary relicts. They
present a strong argument for common ancestry.
Vestigial structures
Æ No apparent purpose
Æ Resemble similar
functional structures in
other, closely related
species
Æ also human appendix
Evolution helps us understand patterns in the diversity of life
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V. Comparative Embryology
Embryological stages
V. Embryology and Comparative Development
pig
cow
rabbit
human
Æ all vertebrate embryos look
similar early in their
development
Comparative Development Reveals
Descent from a Common Ancestor
Æ evidence of common ancestry
Æ similar developmental
“instructions” in DNA
VI. Genetic Analysis
Modern technology reveals relatedness among diverse
organisms
Molecular Record – Independent test
Æ Distantly related organisms are expected to accumulate a greater
number of evolutionary differences than closely related species.
• Essentially all organisms have DNA as genetic material
• With very few exceptions, all organisms use the same
genetic code
• Similarities in genes and proteins exist in predictable ways
(based on morphological similarities)
VII. Biogeographical Evidence
VIII. Conclusions
• Islands often have unique (endemic) species
• Species on islands are most similar to those on
nearest continent (or nearest island)
Species of Gallotia lizards on
the Canary Islands
There are many documented cases of
Evolution in Action
• Darwin’s Finches – beak size
– Grant and Grant – 1970s
• Showed beak size heritable and responsive to
environmental change
• Pesticide and Antibiotic resistance
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VIII. Conclusions: Evolution in Action
Insects: Pesticide resistance
(Florida)
Agent of Natural Selection:
Pesticide called "Combat®"
End Evolution
– Cockroaches who like
bait: continuously killed
– Those who didn’t like
bait: survived
• Had rare, glucose
disliking mutation
– Bait now is ineffective>>
populations are resistant
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