Chapter 7
Evolution and the
Fossil Record
1
Guiding Questions
• What evidence convinced Charles Darwin that evolution
produced the species of the modern world?
• What are the mechanisms of evolution?
• What is the source of the genetic variability that is acted on
by „natural selection‟?
• What factors lead to evolutionary radiation?
• Why is convergence evidence that evolutionary changes are
adaptive?
• Why do species become extinct?
• What is mass extinction?
• What are some observed evolutionary trends?
2
Discovery of
Evolution
3
In the late Nineteenth Century
Charles Darwin
Alfred Russell Wallace
Charles Darwin
• 1831
– Set sail on the
Beagle
– Schooled in
Uniformitarianism
• Lyell‟s Principles
of Geology
– Keen observer
– Published Origin of
Species 1859
5
Charles Darwin
• Rhea
– Large flightless
birds
– Found only in
South America
– Also found extinct
fossil forms of large
mammals
6
Charles Darwin
• Sloths and extinct
armadillos
– Unique to the
Americas
7
Charles Darwin
• Oceanic islands
– Thousands of miles
from the mainland
– Many barren
– Animals must have
come from elsewhere
• Galápagos Islands
– Tortoises with
unique shells on each
island
Common ancestry >> Later differentiation
8
Darwin‟s Finches
• Finches of the Galápagos
– Different beak types
• Slender
• Sturdy
• Woodpecker-like
– Differentiation based on
lifestyle
10
Charles Darwin
• Additional observations
– Differences in marine organisms on the Atlantic
and Pacific sides of the Isthmus of Panama
12
Charles Darwin
• Additional observations
– Anatomical relationships
• Embryos of many vertebrates quite similar
• Homology
– Presence of organs in two different groups of
animals or plants that have the same ancestral
origin but serve different functions
• Vestigial organs
– Organs that serve no apparent purpose but
resemble organs that perform functions in other
creatures, note: vestigial DNA
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Mechanisms
of Evolution
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Causes for Diversity of Life
1.
All populations have the potential to increase or decrease in
size
2.
Individuals in a population differ in their abilities
•
Some of these abilities affect survival
3. Best adapted individuals are most likely to survive and
produce offspring (Natural Selection)
•
4.
“Abilities” are passed on to offspring (Genetics)
Over time the “abilities” of the population shift to include
advantageous traits (Evolution)
Net Result:
Populations change with time to
become better adapted to their
environment (Evolution),
„a tautology‟
Example: Microbe
Resistance
Apply Antibiotic
Survivor‟s with Resistance Reproduce
Theory of Evolution
• Natural Selection
– Process that operates in nature but parallels the
artificial selection by which breeders develop
new varieties of plants and animals
– Success of an individual determined by
advantages it has over others
– Survivors bear offspring with same trait
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How does it Work?
Variation in the Gene Pool of a Population
Theory of Evolution
• Genes
– Hereditary factors
• Particulate inheritance
– Gregor Mendel: Organisms retain identities
through generations
– Peas
• No blending
• Colors could be masked for generations
20
Theory of Evolution
• Mutations
– Alteration of genes
– Provides for variability
• DNA
– Deoxyribonucleic acid
– Transmits chemically
coded information
– Concentrated in
chromosomes
• paired
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23 Pairs of Human Chromosomes
The haploid human genome contains an estimated 20,000–25,000 protein-coding
genes, far fewer than had been expected before its sequencing.[1] In fact, only
about 1.5% of the genome codes for proteins, while the rest consists of RNA
genes, regulatory sequences, introns and (controversially) "junk" DNA.[2]
How do mutations occur?
Errors in DNA Replication
On average 1:10,000-100,000
genes per individual per generation
DNA destruction by exposure to radiation,
chemicals etc.
Most Mutations are bad or neutral, but
some are good
What is “good” depends on environmental conditions
Manipulation of HOX regulatory genes creates a
mutant house fly
Theory of Evolution
• Sexual recombination
– Each parent contributes one-half of its chromosomes to offspring
– Gamete
• Special reproductive cell contains one of each type of chromosome
– Female egg; male sperm
– Yields new combinations
• Mutations increase variability
• Gene pool
– Sum total of genetic components of a population or group of interbreeding
individuals
• Reproductive barriers limit the pool
• Speciation
– Origin of a new species from two or more individuals of a preexisting species
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Origination Rates
• Rates
– Galápagos Islands
• Formed millions of years ago
– Lake Victoria
• 13,000 years old
• 497 unique species of cichlid fish
• Specialized adaptations
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Origination
• Evolutionary radiations
• Adaptive breakthrough
– Pattern of expansion from some
– Appearance of key features that allow
ancestral adaptive condition
radiation to occur
represented by descendant taxa • Fossil record documents patterns
– Jurassic corals
Modern hexacorals expanded rapidly during the Jurassic
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Most suborders in the early Jurassic
Many families before the end of the Jurassic
• Molecular clocks
– Assume average rate of mutation of
„neutral‟ genes
– Determine number of mutations
– Extrapolate timing split in gene pools
Promising but still many
problems
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Extinction
• Caused by extreme impacts of
limiting factors
– Predation
– Disease
– Competition
• Pseudoextinction
– Species evolutionary
line of descent continues
but members are given a
new name
• High rates of extinction
make useful index
fossil
– Ammonoids
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Extinction
• Rates
– Average rate of
extinction has declined
through time
• Mass extinctions
– Many extinctions within
a brief interval of time
– Largest events peak at
extinction of > 40%
genera
– Rapid evolutionary
radiation follows
32
Modern Mass Extinctions
• Fossil patterns
reflected in modern
times
– Tropical species
– Large animals
• Loss of habitat
• Direct exploitation
• Likely replacement
by opportunistic
species
33
Evolutionary Trends
• Cope‟s rule
– Body size increases
during evolution of a
group of animals
– Structural limitations
on size
• Specialized
adaptations limit
evolution
– Elephants
– Manatees
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Evolutionary Trends
• Whales
– Terrestrial origin
• 50 M years ago
• Small (2 m)
mammals with feet
– Marine adaptation
•
•
•
•
40 M years ago
Lost hind limbs
No pelvic bones
Up to 20 m
35
Phylogeny
• Horses
– Increase in body size
– Evolved tall, complex
molars, and single-hoofed
toe
– Change driven by climate
• Expansion of
grasslands
37
Phylogeny
• Rates
• Gradualistic Model
– Very slow rates
• Punctuational Model
– Rapid evolution with
little change between
steps
– Bowfin fish
• Little change in 60
Million years
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Phylogeny
• Complex, largescale trend within a
branching tree of
life
• Gradual large-scale
change from one
species to another
is rare
– Jurassic coiled
oysters
39
Phylogeny
• Axolotl
– Example of rapid
speciation from
parent species
• Parent is
amphibious
• Offspring is aquatic
throughout life after
one simple genetic
change
40
• Dollo‟s law
– Evolutionary transition from at
least several genetic changes is
unlikely to be reversed by
subsequent evolution
„You can‟t go home again‟
43
Evidence for
Evolution
Evidence for Evolution: Fossils
& Faunal Succession
Evidence for Evolution:
Analogous/Convergent Structures
Evidence for Evolution:
Homologous Structures
Evidence for Evolution: Vestigial
Structures
Evidence for
Evolution:
Biochemistry of
Life
DNA, ATP,
amino acids,
chirality, lipid
structures
Evidence for
Evolution:
Gene
Sequencing
Evidence for Evolution:
Artificial Selection
Evidence for Evolution:
Artificial Selection
Some Interesting
Effects of Evolution
Extinction
Species A
Sometimes a species cannot
adapt fast enough to
environmental change or
competition
No moa, no moa,
In old Ao-tea-roa.
Can‟t get „em.
They‟ve et „em.
They‟ve gone and there ain‟t no moa!
Moa
Extinctions through time
Evolution & Speciation
Species B
Species A
Species A is separated into 2
isolated populations, each
affected by different
environmental conditions
Species C
In effect, Species A goes Extinct
Evolutionary Convergence
• Evolution of similar
forms in two or more
different biological
groups
• Marsupials and
placental mammals
– Similar form
– Isolated, adaptive
convergent evolution
after initial divergence
58
Convergent Evolution
Coevolution:
Plants and Pollinators
Coevolution:
Predator/Prey
63
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