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Evolutionary Patterns, Rates, and
Trends
Chapter 13
Asteroid Impacts
• Many past catastrophic
impacts altered the course of
evolution
• Iridium layer implicates
asteroid in extinction of
dinosaurs
• Asteroids are still a threat
Macroevolution
Large-scale patterns, trends,
and rates of change among
families and other more inclusive
groups of species
Impacts, Issues Video
Measuring Time
Fossils
• Recognizable evidence of ancient life
What do Fossils Tell Us?
• Each species is a mosaic of ancestral and
novel traits
• All species that ever evolved are related to
one another by way of descent
Stratification
• Fossils are found in
sedimentary rock
• This type of rock is formed
in layers
• In general, layers closest to the
top were formed most recently
Sedimentary Rock
Radiometric Dating
• Organism becomes
buried in ash or
sediments
• Organic remains
become infused with
metal and mineral ions
• Carbon 14 dating
Radiometric Dating
parent isotope in
newly formed rock
after one half-life
after two half-lives
Radiometric Dating
Radioisotope decay
Radiometric dating
Geologic
Time
Scale
• Boundaries
based on
transitions
in fossil
record
Phanerozoic
eon
Cenozoic
era
Mesozoic
era
Quaternary period
Tertiary period
65
Cretaceous period
145
Jurassic period
Triassic period
Paleozoic
era
213
248
Permian period
286
Carboniferous period
360
Devonian period
Silurian period
Ordovician period
Cambrian
Cambrianperiod
period
410
440
505
544
Proterozoic eon
Archean eon and earlier
2,500
mya
Geologic time scale
Record Is Incomplete
• Fossils have been found for
about 250,000 species
• Most species weren’t
preserved
• Record is biased toward the
most accessible regions
Macroevolution
• Major patterns and trends among
lineages
• Rates of change in geologic time
Continental Drift
• Continents were once joined and have
since “drifted” apart
• Initially based on shapes
• Later supported by world distribution of
fossils and existing species, orientation
of particles in iron-rich rocks
Plate Tectonics
• Earth’s crust is fractured into plates
Geologic forces
Plate Tectonics
• Movement of plates is driven by upwelling of
molten rock at mid-oceanic ridges
island arc
oceanic crust
lithosphere
hot
(solid layer of mantle) spot
oceanic ridge trench
athenosphere
(plastic layer of mantle)
continental crust
subducting
plate
Fig. 13-6a, p.199
Plate margins
Comparative Morphology
• Comparing body forms and structures of
major lineages
• Guiding principle:
– When it comes to introducing change in
morphology, evolution tends to follow the
path of least resistance
4
Morphological
Divergence
3
early
reptile
21
5
21
3
• Change from
body form of a
common
ancestor
4
pterosaur
1
chicken
2
3
1
2
bat
3 4
• Produces
homologous
structures
1
5
porpoise
2
4
3
5
penguin
2
1
2
3
4
5
3
human
Morphological divergence
Morphological Convergence
• Individuals of different
lineages evolve in similar
ways under similar
environmental pressures
• Produces analogous
structures that serve similar
functions
Morphological Convergence
Comparative Development
• Each animal or plant proceeds through a
series of changes in form
• Similarities in these stages may be clues
to evolutionary relationships
• Mutations that disrupt a key stage of
development are selected against
Proportional Changes in Skull
Mutation and proportional changes
Molecular Evidence
• Biochemical traits shared by species
show how closely they are related
• Can compare DNA, RNA, or proteins
Biological Species Concept
“Species are groups of interbreeding
natural populations that are
reproductively isolated from other
such groups.”
Ernst Mayr
Genetic Divergence
• Gradual accumulation of differences in
the gene pools of populations
• Natural selection, genetic drift, and
mutation can contribute to divergence
• Gene flow counters divergence
Reproductive Isolation
• Cornerstone of the biological
species concept
• Speciation is the attainment of
reproductive isolation
• Reproductive isolation arises as a
by-product of genetic change
Reproductive Isolating
Mechanisms
• Prevent pollination or mating
• Block fertilization or embryonic
development
• Cause offspring to be weak or sterile
Reproductive
Isolation
Mechanisms
Isolating Mechanisms
Reproductive isolating mechanisms
Prezygotic Isolation
Mechanical isolation
Temporal isolation
Behavioral isolation
Ecological isolation
Gametic mortality
Mechanical
Isolation
• Wasp and zebra
orchid
Temporal
Isolation
• Cicada
Reproductive Isolation
Temporal isolation among cicadas
Behavioral Isolation
• Albatrosses
Reproductive Isolation
Albatross courtship
Postzygotic Mechanisms
Early death
Sterility
Low survival rates
Models for Speciation
• Allopatric speciation
• Sympatric speciation
• Parapatric speciation
Models for Speciation
Models of Speciation
Allopatric Speciation
• Speciation in geographically isolated
populations
• Some sort of barrier arises and prevents
gene flow
• Effectiveness of barrier varies with
species
Allopatric Speciation
Extensive Divergence Prevents
Inbreeding
• Species separated by geographic
barriers will diverge genetically
• If divergence is great enough it will
prevent inbreeding even if the barrier
later disappears
Archipelagos
• Island chains some distance from
continents
– Galapagos Islands
– Hawaiian Islands
• Colonization of islands followed by
genetic divergence sets the stage for
speciation
Models of Speciation
Allopatric speciation on an archipelago
Hawaiian Islands
• Volcanic origins, variety of habitats
• Adaptive radiations:
– Honeycreepers: in absence of other
bird species, they radiated to fill
numerous niches
Ancestral Type
Housefinch (Carpodacus)
Fig. 13-18d13, p.209
Speciation in Hawaiian Honeycreepers
Akepa (Loxops coccineus)
Fig. 13-18d1, p.209
Speciation without a Barrier
• Sympatric speciation
– Species forms within the home range of the
parent species
• Parapatric speciation
– Neighboring populations become distinct
species while maintaining contact along a
common border
Sympatric Speciation in African
Cichlids
• Studied fish species in two lakes
– Species in each lake are most likely
descended from single ancestor
• No barriers within either lake
Sympatric Speciation in African Cichlids
• Feeding preferences localize species in
different parts of lake
Parapatric Speciation
• Populations in contact along a common border
giant
velvet
worm
blind
velvet
worm
We’re All Related
• All species are related by descent
• Share genetic connections that
extend back in time to the
prototypical cell
Evolutionary Trees
species 2
species 3
species 1
ancestral
stock
Summarize
information
about
relationships
among groups
Evolutionary Trees
Evolutionary tree diagram
Gradual Model
• Species emerge through
many small changes
accumulating over time
• Fits well with evidence from
certain lineages in fossil
record
Punctuation Model
• Speciation model in which most changes
in morphology are compressed into brief
period near onset of divergence
• Supported by fossil evidence in
some lineages
Adaptive Radiation
• Burst of divergence
• Single lineage gives rise to many new
species
• New species fill vacant
adaptive zone
• Adaptive zone is “way of life”
• Cenozoic radiation of mammals
Adaptive
Radiations of
Mammals
Extinction
• Irrevocable loss of a species
• Mass extinctions play a major role in
evolutionary history
• Fossil record shows 20 or more largescale extinctions
• Reduced diversity is followed by
adaptive radiation
Who Survives?
• Species survival is somewhat random
• Asteroids have repeatedly struck Earth,
destroying many lineages
• Changes in global temperature favor
lineages that are widely distributed
Taxonomy
• The identification, naming, and
classification of species
• Somewhat subjective
• Information about species can be
interpreted differently
Naming Species
• Each species has a two-part name
• First part is generic name
• Second part is species name
• Ursus arctos = brown bear
Ursus americanus = black bear
Bufo americanus = American toad
Higher Taxa
• Kingdom
• Phylum
• Class
• Order
• Family
• Inclusive groupings
reflect assumed
relationships among
species
Examples of Classification
western juniper
Kingdom
Phylum
Class
Order
Family
Genus
Species
Plantae
Coniferophyta
Coniferopsida
Cuoniferales
Cupressaceae
Juniperus
J. occidentalis
vanilla orchid
Plantae
Anthophyta
Monocotyledonae
Asparagales
Orchidaceae
Vanilla
V. planifolia
housefly
Animalia
Anthropoda
Insecta
Diptera
Muscidae
Musca
M. domestica
human
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
H. sapiens
Phylogeny
• The scientific study of evolutionary
relationships among species
• Practical applications
– Allows predictions about the needs or
weaknesses of one species on the basis of
its known relationship to another
Six-Kingdom Classification
Bacteria
Archaea
Protists
Plants
Fungi
Animals
Three-Domain System
Bacteria
Archaea
Eukarya
Evolutionary
Tree
Evolutionary Tree
Current evolutionary tree
Table 13-1, p.216
Llama-Camel Hybrid