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Evidence of Evolution
Chapter 16
Biology Concepts and Applications, Eight Edition, by Starr, Evers, Starr. Brooks/Cole,
Cengage Learning 2011.
16.1 Early Discoveries
 By the 19th century, advances in geology,
biogeography, and comparative morphology
resulted in awareness of change in lines of
descent of species
Geological Evidence
Asteroids: small planets
size 1-1,500 kilometers
Mile wide Barringer Crater in
Arizona 300,000 ton
asteroid, 50,000 years ago.
Impact 150x greater than
Hiroshima bomb
Geological Evidence
 Mass extinction
• Permanent loss of major groups of organisms
• Occurred 65.5 million years ago
• Event marked by unusual, worldwide layer of rock
called the K-T boundary layer
• Below layer  Dinosaur fossils
• Above layer  no Dinosaur fossils
• Impact crater off the coast of the Yucatan Peninsula
dates about 65.5 million years ago
 Inferred from evidence 
• 20 km or 12 mile wide asteroid wiped out the
dinosaurs
16.2 Early Beliefs, Confounding Discoveries
 Aristotle  Naturalist
• Person who observes life from a scientific perspective
• Viewed nature as a continuum of organization, from
lifeless matter through complex plants and animals
• “Great chain of being”
• From the lowest form (snakes) to humans and even
spiritual beings
• Chain links = a species
• Each new species discovered was another link in the chain
of being
• Chain = complete and continuous
• Once chain is complete  meaning of life would be
revealed
Early Beliefs, Confounding Discoveries
 Alfred Wallace  Biogeography
• Study of patterns in the geographic distribution of
species and communities
• Looked at the natural forces that shape life
• Raised ?
• Isolated species look suspiciously similar to
species living across vast expansions of open
ocean, or on the other side of mountain ranges
Early Beliefs, Confounding Discoveries
Rhea
South America
Ostrich
Africa
All flightless birds.
Long, muscular legs.
Emu
Australia Inhabit flat, open grasslands
about the same distance from
the equator.*Common Ancestors!
Comparative Morphological Evidence
 Comparative Morphology
• Study of body parts and structures among groups
of organisms
 Organisms outwardly similar but different
internally
• Fish and porpoises  Very different
 Outwardly different but similar internally
• Human arm and porpoise flipper
• Elephant leg and bat wing
 Useless parts 
• leg bones in snakes or vestiges of tail in humans
Comparative Morphological Evidence
Fossil Evidence
Fossil  physical evidence
Of an organism that lived
In the ancient past
Mapping rock formation:
Deeper layers hold
Fossils of simple marine
Life. Layers above held
Similar but more intricate
Fossils. Higher layers,
Similar that belong to
Modern species.
16.3 Evolution:
Development of New Theories
 Evolution
• Change that occurs in a line of descent (lineage)
 19th-century naturalists tried to reconcile traditional
beliefs with evidence of evolution
• Georges Cuvier’s theory of catastrophism
• Now abandoned hypothesis that catastrophic geologic
forces unlike those of the present day shaped Earth’s
surface
• Lamarck’s theory of inheritance of acquired
characteristics due to environmental factors
• Species gradually improved over generations to drive
to perfection. Ex. Giraffe  long neck
Voyage of the Beagle
 Charles Darwin’s observations on a voyage
around the world led to new ideas about species
• Theory of uniformity (gradual, repetitive change)
• Idea that gradual repetitive
processes occurring over
long time spans shaped
Earth’s surface
• Theory challenged idea that
Earth was 6,000 yrs old
**However, must have taken
longer to sculpt Earth’s surface
Voyage of the Beagle
Key Concepts: EMERGENCE OF
EVOLUTIONARY THOUGHT
 Long ago, Western scientists started to catalog
previously unknown species and think about
their global distribution
 They discovered similarities and differences
among major groups, including those
represented as fossils in layers of sedimentary
rock
16.4 Descent with Modification
 Darwin compared the modern armadillo with the
extinct glyptodont
Glyptodont – Argentina
Extinct but similar to Armadillo
Armadillo – live only in
Places the Glyptodont once lived
Variations in Traits
 Darwin observed that variations in traits
influence an individual’s ability to secure
resources – to survive and reproduce
A Key Insight – Variation in Traits
 Adaptation (adaptive trait)
• A heritable trait the enhances an individual’s fitness
 Artificial selection
• Selective breeding of animals by humans
Darwin, Wallace, and Natural Selection
 In 1858, Charles Darwin and Alfred Wallace
independently proposed a new theory, that
natural selection can bring about evolution
Theory of Natural Selection
 Natural selection
• Process in which environmental pressures result in the
differential survival and reproduction of individuals of a
population who vary in the details of shared, heritable
traits
• Can lead to increased fitness
 Fitness
• Degree of adaptation to an environment, as measured
by an individual’s relative genetic contribution to future
generations.
Main Premises of the
Theory of Natural Selection
1. A population tends to grow until it begins to
exhaust the resources of its environment
2. Individuals must then compete for resources
such as food and shelter from predators
3. Individuals with forms of traits that make them
more competitive tend to produce more offspring
Inferences of the
Theory of Natural Selection
 Environmental factors acting on a range of traits
in a population influence differential survival and
reproduction of individuals (natural selection)
 Forms of heritable traits that impart greater
fitness to an individual become more common in
a population over generations
Key Concepts:
A THEORY TAKES FORM
 Evidence of evolution, or changes in lines of
descent, gradually accumulated
 Charles Darwin and Alfred Wallace
independently developed a theory of natural
selection to explain how heritable traits that
define each species evolve
16.5 Fossil Evidence
 Fossils
• Physical evidence of life in the distant past
 Found in stacked layers of sedimentary rock
• Younger fossils in more recently deposited layers
• Older fossils underneath, in older layers
Fossilization
Fossilization
• Begins when organisms become covered by
sediments or volcanic ash.
• Water seeps into the remains, and metal ions and
other organic compounds dissolved in water replace
the minerals in the bones and hard tissues.
• Pressure and mineralization process transforms the
remains into rock
Stratification
• Layers of
sedimentary rock
made from river silt,
sand, volcanic ash,
and other materials
from land to sea
Interpreting the Fossil Record
 The fossil record is incomplete
• Have fossils for 250,000 known species
• Most times, remains are obliterated by decay
because organic materials decompose in the
presence of oxygen
• Material remains IF encased in air-excluding
materials (sap, tar, ice, or mud)
 Favors species with hard parts, dense
populations with wide distribution, and that
persisted a long time
Dating Fossils
 Geologic time scale  Chronology of Earth’s History
• Boundaries for major intervals determined by
transitions in the fossil record
• Correlated with macroevolutionary events
• Includes dates obtained by radiometric dating
Geologic Time Scale
Macroevolution
 Major patterns, trends, and rates of change
among lineages (Geologic time scale)
Radiometric Dating: Half-Life
 Half-life
• Characteristic time it takes for half
of a quantity of a radioisotope to
decay
• Ex. Uranium 238  thorium 234 
 lead 206 (takes 4.5 billion yrs)
 Predictable radioactive decay
can be used to find the age of a
volcanic rock
Radiometric Dating: Half-Life
 Radioactive dating
• Method of estimating the age of a
rock or fossil by measuring the
content and proportions of a
radioisotope and its daughter
elements
• Oldest terrestrial rock (tiny zircon
crystal) in Australia
• 4.404 billion years old
• Recent fossils that still contain
carbon can by dated by measuring
their carbon 14 content
• Complete decay of 14C occurs in
60,000 years
Parent isotope remaining (%)
parent isotope in
newly formed rock
100
75
after one half-life
50
after two half-lives
25
0
1
2
3
4
Time (half-life) for any radioisotope
a A simple way to think about the decay of a radioisotope to a more
stable isotope, as plotted against time.
Fig. 16.11a, p.248
Fig. 16.11b-d, p.248
Key Concepts:
EVIDENCE FROM FOSSILS
 The fossil record offers physical evidence of past
changes in lines of descent
16.7 Plate Tectonics Theory
 Movements of Earth’s tectonic plates rafted land
masses to new positions
 Pangea: First ancient supercontinent that formed
about 237 million years ago and broke up about
152 million years ago
• Gondwana  supercontinent that existed before
Pangae, more than 500 million years ago
• Include Southern Hemisphere and India and
Arabia
• Most modern species live only in places that were
once part of Gondwana
16.7 Plate Tectonics Theory
 Plate Tectonics OR Continental drift
• Theory that Earth’s outer layer of rock is cracked into
plates
• Slow movement of which rafts continents to new locations
over geologic time
 Movements had profound impacts on the directions of
life’s evolution
• Evidence of at least 5x since Earth’s outer layer solidified
4.55 billion years ago, a single supercontinent with one
ocean lapping the coast line formed and then split up.
• 14 million years ago, that Earth and it’s continents mirror
today
Evidence of Drifting Continents
 Evidence for plate tectonics theory
•
•
•
•
•
Distribution of global land masses
Global fossil distribution
Magnetic rocks
Seafloor spreading from mid-oceanic ridges
In faults (fault lines)
• Volcanic island chains  form as a plate moves
across an undersea hot spot (place where a
narrow plume of molten rock wells up from deep
inside Earth and ruptures a plate
Forces of Plate Tectonics
island arc
oceanic crust
oceanic ridge trench
lithosphere
hot
asthenosphere
(solid layer of mantle) spot (plastic layer of mantle)
continental crust
subducting
plate
Fig. 16.14b, p.250
Drifting Continents
a 420 mya
b 237 mya
c 152 mya
d 66 mya
e 14 mya
Fig. 16.15, p.251
Key Concepts:
EVIDENCE FROM BIOGEOGRAPHY
 Correlating evolutionary theories with geologic
history helps explain the distribution of species,
past and present
16.8 Comparative Morphology
 Comparisons of body form and structure of
major groups of organisms
 Reveals evolutionary connections among
lineages
Morphological Divergence
 Homologous structures:
• Similar body parts that became modified
differently in different lineages
 Evidence of descent from a common ancestor
 Morphological divergence
• Evolutionary pattern in which a body part of an
ancestor changes in its descendants
Homologous
Structures
Morphological
Divergence
1
2
3
4
stem reptile
5
Fig. 16.16a, p.252
2
3
1
pterosaur
4
Fig. 16.16b, p.252
1
2
3
chicken
Fig. 16.16c, p.252
2
3
penguin
Fig. 16.16d, p.252
1
porpoise
4
2
5
3
Fig. 16.16e, p.252
1
2
bat
3
4
5
Fig. 16.16f, p.252
1
2
3
4
5
human
Fig. 16.16g, p.252
1
2
3
4
5
elephant
Fig. 16.16h, p.252
Morphological Convergence
 Analogous structures:
• Body parts in different lineages that look alike, but
evolved separately after the lineages diverged
• Did not evolve in a common ancestor
 Morphological convergence
• Evolutionary pattern in which similar body parts
evolve separately in different lineages
Analogous Structures
Morphological convergence
Insects
Bats
Humans
Crocodiles
Birds
wings
wings
wings
limbs with
5 digits
Fig. 16.17d, p.253
16.9 Changes in Patterns of Development
 Similarities in patterns of embryonic
development suggest shared ancestry
 Mutations in genes that affect development may
cause morphological shifts in a lineage
 Gene duplications account for some differences
between closely related lineages
Comparative Embryology:
Vertebrate Relationships
Human
Mouse
Bat
Chicken
Alligator
All vertebrate embryos have similar stages:
- Stage with 4 limb buds, a tail, and divisions called somites
along their back
Chimps and Humans:
Genes That Control Growth Rate
Key Concepts: EVIDENCE FROM
COMPARATIVE MORPHOLOGY
 Species of different lineages often have similar
body parts that may be evidence of descent from
a shared ancestor
DNA, RNA, and Proteins
 Comparisons of DNA, RNA, and proteins reveal
and clarify evolutionary relationships
Molecular Clock
 Neutral mutations accumulate in DNA at a
predictable rate
• Help estimate when two lineages diverged
• Mitochondrial DNA (mtDNA) is inherited intact
 Closely related species share more nucleotide
or amino acid sequences than less related ones
Key Concepts: EVIDENCE FROM
COMPARATIVE BIOCHEMISTRY
 Molecular comparisons help us discover and
confirm relationships among species and
lineages
Constructing a Cladogram
 All organisms are related by descent
 Representing life’s history as a tree with
branchings from ancestral stems clarifies
relationships
Constructing a Cladogram
Fig. 16.27a, p.260
Fig. 16.27c, p.260
Fig. 16.27d, p.260
Life’s Evolutionary History
Key Concepts:
ORGANIZING THE EVIDENCE
 Evolutionary tree diagrams are based on the
premise that all species interconnect through
shared ancestors—some remote, others recent
Animation: Comparative pelvic anatomy
Animation: Evolutionary tree diagrams
Animation: Finches of the Galapagos
Animation: Geologic forces
Animation: Interpreting a cladogram
Animation: Morphological divergence
Animation: Mutation and proportional
changes
Animation: Plate margins
Animation: Radioisotope decay
Animation: Radiometric dating
Animation: The Galapagos Islands