Download Evolution = descent with modification

Chapter 21:
Evidence for Evolution
I.
Evolution & Darwin
II. Artificial Selection
III. Fossil Record
IV. Comparative Anatomy
V. Embryology
VI. Genetic Analysis
VII. Biogeographical Evidence
VIII. Conclusions
“Nothing in biology makes sense except in the light of evolution”
--Theodosius Dobzhansky
I. Evolution & Darwin
Evolution = descent with modification
! Macroevolution = large changes
! Microevolution = small changes
Both rely on same mechanisms!
Primarily natural selection
Charles Darwin:
On the Origin of Species
(mid-1800’s)
• Traveled extensively
• Galapagos Islands
– off the coast of Ecuador
• One area of focus: finches
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I. Evolution & Darwin
• Finches of the Galapagos
• 14 species
• Difference between them:
– Beak shape
•
•
•
•
Seed crackers
Cactus eaters
“Tool users”
Vampire
• Darwin’s idea:
– One original species has adapted to different food
sources
II. Artificial Selection
CAN selection produce major evolutionary change?
! 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!
• 3 examples…
A) Plants
!Broccoli, brussel sprouts, kale,
cabbage, & cauliflower
! All artificially selected
from Brassica oleracea
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II. Artificial Selection (cont.)
B) Insects: Pesticide resistance
(Florida)
Agent of Natural Selection:
Pesticide called "Combat®"
– 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
II. Artificial Selection (cont.)
C) Mammals: Dogs
Change can happened
over a very short
geological period if the
selection pressure is
strong!
READ 420-421
SILVER FOX
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III. The Fossil Record
Fossils: Preserved remains of ancient organisms
III. The Fossil Record
How to make a fossil:
! Burial in sediment
! Mineralization of organic
material
! Hardening of sediment
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III. The Fossil Record
Darwin and his contemporaries saw and knew of fossils:
! Local fossils looked like local organisms
! 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
Organization of fossils:
a) Fossils are found in distinct layers
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Organization of fossils:
a) Fossils are found in distinct layers
b) Resemblance to modern forms of
life gradually increases with
younger fossils
c) Many fossils are of species now
extinct
Conclusions:
! Many different types of organisms
in the past (some extinct)
! Change in lineages over time
III. The Fossil Record
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
–Fish, amphibians, reptiles, mammals, and birds appear in order
• Seedless vascular plants, seeds, gymnosperms, and
angiosperms appear in order
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Unstable isotopes decay at a constant and predictable rate
READ 422
Allows setting of absolute age on rock strata.
One conclusion: the Earth is very old ! ~4.5 billion years
How Do We Know That Evolution Has Occurred?
Fossil record
evidence of
evolutionary
change over time
Ancient primitive
organisms !
Several intermediary
stages
!Modern forms
READ 423-425
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Whale Evolution:
Fossil Record of Evolution
Modern toothed whales
Rodhocetus kasrani
reduced hind limbs
could not walk;
swam with up-down motion
like modern whales
Ambulocetus natans
walked on land
…like sea lions
Pakicetus attocki
lived on land;
skull had whale
characteristics
swam
by flexing & paddling
… like otters
READ 422-423
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
III. The Fossil Record: Evidence for Mass Extinctions
Number of families
Diversity over the Last 600 Million Years
800
600
400
200
0
600
Cambrian
(545-490)
500
400
Silurian
(438-408)
Ordovician
(490-438)
300
200
100
Carboniferous Triassic Cretaceous
(360-280)
(248-213) (144-65)
Devonian
(408-360)
Permian Jurassic
(280-248) (213-144)
0
Tertiary
(65-2)
Millions of years ago
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IV. Comparative Anatomy
• Organisms can be grouped (classified) by
unique anatomical characteristics
• Similar anatomy is found in organisms with
greatly divergent functions
Similar anatomy is found in organisms with
greatly divergent functions
Homologous structures
! structures that may have different appearances and
functions, yet all derived from a common ancestor
Evolution helps us understand patterns in the diversity of life
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Vestigial structures are Evolutionary relicts. They
present a strong argument for common ancestry.
Vestigial structures
! No apparent purpose
! Resemble similar
functional structures in
other, closely related
species
! also human appendix
V. Embryology and Comparative Development
Embryological stages
pig
cow
rabbit
human
! All vertebrate embryos look
similar early in their
development
! evidence of common ancestry
! similar developmental
“instructions” in DNA
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V. Embryology and Comparative Development
Comparative Development Reveals
Descent from a Common Ancestor
VI. Genetic Analysis
Modern technology reveals relatedness among diverse
organisms
• 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)
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Molecular Record – Independent test
! Distantly related organisms are expected to accumulate a greater
number of evolutionary differences than closely related species.
VII. Biogeographical Evidence
• 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
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VII. Biogeographical Evidence
• Different continents have different species
• Modern species on any continent are most similar to
fossils on that continent
VIII. Conclusions
Evolution in Action
• Darwin’s Finches – beak size
– Grant and Grant – 1970s
• Showed beak size heritable and responsive to
environmental change
• Guppies – with and without predators
• Pesticide and Antibiotic resistance
• Peppered Moths/Industrialized Melanism!
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VIII. Conclusions
READ 416-417
VIII. Conclusions
Evolution – Supported by Many
Independent Lines of Evidence
! Evolution requires that all of these facts are true
and congruent with each other.
– Fossils, Order of Appearance, Relative and
Absolute Dates
– Anatomical Classification, Vestigial Structures,
Homologies
– Embryology
– Biogeography
– Genetic Analysis
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VIII. Conclusions
Evolution – Both a Fact and a Theory
• That evolution has occurred (and is currently
occurring) is NOT in scientific debate now; it has been
settled.
• FACT – The biodiversity on Earth is a result of
evolution from a common ancestor.
• FACT – Evolution continues today.
• THEORY – The intricacies of evolutionary change and
mechanisms driving evolution.
VIII. Conclusions
Myths
! Evolution is “only a theory”.
– Misuse of word “theory”
– Theory of Gravity, Relativity, Cell theory,
Germ theory of disease etc.
– “Theory” in science means most certain
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End Evolution
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