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How Biological Diversity Evolves
MACROEVOLUTION
Biology and Society:
The Sixth Mass Extinction
 Over the past 600 million years the fossil record reveals five
periods of extinction when 50–90% of living species
suddenly died out.
© 2010 Pearson Education, Inc.
Figure 14.00
 Our current rate of extinction, over the past 400 years,
indicates that we may be living in, and contributing to, the
sixth mass extinction period.
 Mass extinctions:



Pave the way for the evolution of new and diverse forms, but
Take millions of years for Earth to recover
The most “famous” mass-extinction is the K-T Mass Extinction
which included the extinction of the dinosaurs (except birds).
This will be discussed in Chapter 17.
MACROEVOLUTION AND THE DIVERSITY OF LIFE
 Macroevolution:
 Encompasses the major biological changes evident in the fossil
record
 Includes the formation of new species
THE ORIGIN OF SPECIES
 Species is a Latin word meaning:


“Kind” or
“Appearance.”
What Is a Species?
 The biological species concept defines a species as

“A group of populations whose members have the potential to
interbreed and produce fertile offspring”
It is also sometimes stated like this:
 “A group of populations whose members share a common gene
pool and are potentially interbreeding”
 Speciation:


Is the focal point of macroevolution
May occur based on two contrasting patterns, non-branching
and branching.
 In non-branching evolution:


A population transforms but does not create a new species
Actually, it may, but the hypothesis is usually untestable.
 In branching evolution, one or more new species branch
from a parent species that may:


Continue to exist in much the same form or
Change considerably
Similarity between different species
Diversity within one species
Figure 14.2
 The biological species concept cannot be applied in all
situations, including:


Fossils
Asexual organisms
Reproductive Barriers/Isolating Mechanisms between Species
 What’s the logic of isolating mechanisms/reproductive
barriers?
?
Reproductive Barriers between Species
 Prezygotic barriers prevent mating or fertilization
between species.
 Below are some examples you can see at MasteringBiology
Video: Albatross Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship Ritual
INDIVIDUALS OF
DIFFERENT SPECIES
Prezygotic Barriers
Temporal isolation
Habitat isolation
Behavioral isolation
MATING ATTEMPT
Mechanical isolation
Gametic isolation
FERTILIZATION
(ZYGOTE FORMS) Postzygotic Barriers
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
VIABLE, FERTILE
OFFSPRING
Figure 14.3
PREZYGOTIC BARRIERS
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Habitat Isolation
Gametic Isolation
Figure 14.4
 Postzygotic barriers operate if:


Interspecies mating occurs and
Hybrid zygotes form
INDIVIDUALS OF
DIFFERENT SPECIES
Prezygotic Barriers
Temporal isolation
Habitat isolation
Behavioral isolation
MATING ATTEMPT
Mechanical isolation
Gametic isolation
FERTILIZATION
(ZYGOTE FORMS) Postzygotic Barriers
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
VIABLE, FERTILE
OFFSPRING
Figure 14.3
 Postzygotic barriers include:



Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
POSTZYGOTIC BARRIERS
Reduced Hybrid Viability Reduced Hybrid Fertility
Horse
Donkey
Mule
Figure 14.5
Hybrid Breakdown
Mechanisms of Speciation
 A key event in the potential origin of a species occurs when
a population is severed from other populations of the
parent species.
 Species can form by:


Allopatric speciation, due to geographic isolation
Sympatric speciation, without geographic isolation
Allopatric speciation
Simpatric speciation
Figure 14.6
Allopatric Speciation
 Geologic processes can:


Fragment a population into two or more isolated populations
Contribute to allopatric speciation
Video: Lava Flow
Video: Volcanic Eruption
Video: Grand Canyon
Ammospermophilus harrisii
Ammospermophilus leucurus
Figure 14.7
 Speciation occurs only with the evolution of reproductive barriers
between the isolated population and its parent population.
Populations
become
allopatric
Populations
become
sympatric
Populations
interbreed
Gene pools merge:
No speciation
Geographic
barrier
Populations
cannot
interbreed
Reproductive
isolation:
Speciation has
occurred
Time
Figure 14.8
Sympatric Speciation
 Sympatric speciation occurs:
 While the new species and old species live in the same time and
place
 If a genetic change produces a reproductive barrier between the
new and old species
 Polyploids can:


Originate from accidents during cell division
Result from the hybridization of two parent species
 Many domesticated plants are the result of sympatric
speciation, including:







Oats
Potatoes
Bananas
Peanuts
Apples
Coffee
Wheat
Domesticated
Triticum monococcum
(14 chromosomes)
BB
AA
Wild Triticum
(14 chromosomes)
AB
Sterile hybrid
(14 chromosomes)
T. turgidum
Emmer wheat
(28 chromosomes)
AA BB
DD
Wild
T. tauschii
(14 chromosomes)
ABD
Sterile hybrid
(21 chromosomes)
AA BB DD
T. aestivum
Bread wheat
(42 chromosomes)
Figure 14.9-4
Figure 14.9a
What Is the Tempo of Speciation?
 There are two contrasting models of the pace of evolution:


The gradual model, in which big changes (speciations) occur by
the steady accumulation of many small changes
The punctuated equilibria model, in which there are

Long periods of little change, equilibrium, punctuated by

Abrupt episodes of speciation
Punctuated
model
Time
Graduated
model
Figure 14.10
THE EVOLUTION OF BIOLOGICAL NOVELTY
 What accounts for the evolution of biological novelty?
Adaptation of Old Structures for New Functions
 Birds:


Are derived from a lineage of earthbound reptiles
Evolved flight from flightless ancestors
Wing claw
(like reptile)
Teeth
(like reptile)
Feathers
Long tail with
many vertebrae
(like reptile)
Fossil
Artist’s reconstruction
Figure 14.11
 An exaptation:


Is a structure that evolves in one context, but becomes adapted
for another function
Is a type of evolutionary remodeling
 Exaptations can account for the gradual evolution of novel
structures.
 Bird wings are modified forelimbs that were previously
adapted for non-flight functions, such as:



Thermal regulation
Courtship displays
Camouflage
 The first flights may have been only glides or extended
hops as the animal pursued prey or fled from a predator.
Evo-Devo: Development and Evolutionary Novelty
 A subtle change in a species’ developmental program can
have profound effects, changing the:



Rate
Timing
Spatial pattern of development
© 2010 Pearson Education, Inc.
 Evo-devo, evolutionary developmental biology, is the
study of the evolution of developmental processes in
multicellular organisms.
 Paedomorphosis:


Is the retention into adulthood of features that were solely
juvenile in ancestral species
Has occurred in the evolution of

Axolotl salamanders

Humans
Animation: Allometric Growth
Gills
Figure 14.12
Chimpanzee fetus
Chimpanzee adult
Human fetus
Human adult
(paedomorphic features)
Figure 14.13
 Homeotic genes are master control genes that regulate:



When structures develop
How structures develop
Where structures develop
 Mutations in homeotic genes can profoundly affect body
form.
EARTH HISTORY AND MACROEVOLUTION
 Macroevolution is closely tied to the history of the Earth.
Geologic Time and the Fossil Record
 The fossil record is:


The sequence in which fossils appear in rock strata
An archive of macroevolution
Figure 14.14
Figure 14.14a
Figure 14.14b
Figure 14.14c
Figure 14.14d
Figure 14.14e
 Geologists have established a geologic time scale
reflecting a consistent sequence of geologic periods.
Animation: The Geologic Record
Animation: Macroevolution
Table 14.1
Table 14.1a
Table 14.1b
Table 14.1c
Table 14.1d
 Fossils are reliable chronological records only if we can
determine their ages, using:


The relative age of fossils, revealing the sequence in which groups
of species evolved, or
The absolute age of fossils, requiring other methods such as
radiometric dating
 Radiometric dating:



Is the most common method for dating fossils
Is based on the decay of radioactive isotopes
Helped establish the geologic time scale
Carbon-14 radioactivity
(as % of living organism’s
C-14 to C-12 ratio)
Radioactive decay
of carbon-14
100
75
50
25
0
0
5.6 11.2 16.8 22.4 28.0 33.6 39.2 44.8 50.4
Time (thousands of years)
How
carbon-14
dating is
used to
determine
the vintage
of a
fossilized
clam shell
Carbon-14 in shell
Figure 14.15
Plate Tectonics and Macroevolution
 The continents are not locked in place. Continents drift
about the Earth’s surface on plates of crust floating on a
flexible layer called the mantle.
 The San Andreas fault is:


In California
At a border where two plates slide past each other
Figure 14.16
 About 250 million years ago:





Plate movements formed the supercontinent Pangaea
The total amount of shoreline was reduced
Sea levels dropped
The dry continental interior increased in size
Many extinctions occurred
Cenozoic
Present
65
Eurasia
Africa
India
South
America Madagascar
Mesozoic
Laurasia
Paleozoic
251 million years ago
135
Antarctica
Figure 14.17
 About 180 million years ago:




Pangaea began to break up
Large continents drifted increasingly apart
Climates changed
The organisms of the different biogeographic realms diverged
 Plate tectonics explains:
 Why Mesozoic reptiles in Ghana (West Africa) and Brazil look so
similar
 How marsupials were free to evolve in isolation in Australia
Mass Extinctions and Explosive Diversifications of Life
 The fossil record reveals that five mass extinctions have
occurred over the last 600 million years.
 The Permian mass extinction:


Occurred at about the time the merging continents formed
Pangaea (250 million years ago)
Claimed about 96% of marine species
© 2010 Pearson Education, Inc.
 The Cretaceous extinction:



Occurred at the end of the Cretaceous period, about 65 million
years ago
Included the extinction of all the dinosaurs except birds
Permitted the rise of mammals
The Process of Science:
Did a Meteor Kill the Dinosaurs?
 Observation: About 65 million years ago, the fossil record
shows that:





The climate cooled
Seas were receding
Many plant species died out
Dinosaurs (except birds) became extinct
A thin layer of clay rich in iridium was deposited
© 2010 Pearson Education, Inc.
 Question: Is the iridium layer the result of fallout from a
huge cloud of dust that billowed into the atmosphere when
a large meteor or asteroid hit Earth?
 Hypothesis: The mass extinction 65 million years ago was
caused by the impact of an extraterrestrial object.
 Prediction: A huge impact crater of the right age should be
found somewhere on Earth’s surface.
 Results: Near the Yucatán Peninsula, a huge impact crater
was found that:



Dated from the predicted time
Was about the right size
Was capable of creating a cloud that could have blocked enough
sunlight to change the Earth’s climate for months
Figure 14.18-1
Figure 14.18-2
Chicxulub
crater
Figure 14.18-3
CLASSIFYING THE DIVERSITY OF LIFE
 Systematics focuses on:


Classifying organisms
Determining their evolutionary relationships
 Taxonomy is the:



Identification of species
Naming of species
Classification of species
Some Basics of Taxonomy
 Scientific names ease communication by:


Unambiguously identifying organisms
Making it easier to recognize the discovery of a new species
 Carolus Linnaeus (1707–1778) proposed the current
taxonomic system based upon:


A two-part name for each species (binomial nomenclature)
A hierarchical classification of species into broader groups of
organisms
Naming Species
 Each species is assigned a two-part name or binomial,
consisting of:


The genus
A name unique for each species
 The scientific name for humans is Homo sapiens, a two part
name, italicized and latinized, and with the first letter of
the genus capitalized.
Hierarchical Classification
 Species that are closely related are placed into the same genus.
Leopard (Panthera pardus)
Tiger (Panthera
tigris)
Lion (Panthera leo)
Jaguar (Panthera onca)
Figure 14.19
 The taxonomic hierarchy extends to progressively broader
categories of classification, from genus to:






Family
Order
Class
Phylum
Kingdom
Domain
Species
Panthera
pardus
Genus
Panthera
Leopard
(Panthera pardus)
Family
Felidae
Order
Carnivora
Class
Mammalia
Phylum
Chordata
Kingdom
Animalia
Domain
Eukarya
Figure 14.20
Classification and Phylogeny
 The goal of systematics is to reflect evolutionary
relationships.
 Biologists use phylogenetic trees to:


Depict hypotheses about the evolutionary history of species
Reflect the hierarchical classification of groups nested within
more inclusive groups
Order
Family
Felidae
Genus
Species
Panthera
Panthera
pardus
(leopard)
Mephitis
Mephitis
mephitis
(striped skunk)
Carnivora
Mustelidae
Lutra
Lutra
lutra
(European
otter)
Canis
latrans
(coyote)
Canidae
Canis
Canis
lupus
(wolf)
Figure 14.21
Sorting Homology from Analogy
 Homologous structures:


Reflect variations of a common ancestral plan
Are the best sources of information used to

Develop phylogenetic trees

Classify organisms according to their evolutionary history
 Convergent evolution:


Involves superficially similar structures in unrelated organisms
Is based on natural selection
 Similarity due to convergence:


Is called analogy, not homology
Can obscure homologies
Systematics
 Molecular systematics:


Compares DNA and amino acid sequences between organisms
Can reveal evolutionary relationships
 Some fossils are preserved in such a way that DNA
fragments can be extracted for comparison with living
organisms.
Figure 14.22
The Cladistic Revolution
 Cladistics is the scientific search for clades.
 A clade:


Consists of an ancestral species and all its descendants
Forms a distinct branch in the tree of life
Iguana
Outgroup
(reptile)
Duck-billed
platypus
Hair, mammary
glands
Gestation
Kangaroo
Ingroup
(mammals)
Beaver
Long gestation
Figure 14.23
 Cladistics has changed the traditional classification of
some organisms, including the relationships between:





Dinosaurs
Birds
Crocodiles
Lizards
Snakes
Lizards
and snakes
Crocodilians
Pterosaurs
Common
ancestor of
crocodilians,
dinosaurs,
and birds
Ornithischian
dinosaurs
Saurischian
dinosaurs
Birds
Figure 14.24
Classification: A Work in Progress
 Linnaeus:


Divided all known forms of life between the plant and animal
kingdoms
Prevailed with his two-kingdom system for over 200 years
 In the mid-1900s, the two-kingdom system was replaced by
a five-kingdom system that:


Placed all prokaryotes in one kingdom
Divided the eukaryotes among four other kingdoms
 In the late 20th century, molecular studies and cladistics
led to the development of a three-domain system,
recognizing:


Two domains of prokaryotes (Bacteria and Archaea)
One domain of eukaryotes (Eukarya)
Animation: Classification Schemes
Domain Bacteria
Earliest
organisms
Domain Archaea
The protists
(multiple
kingdoms)
Kingdom
Plantae
Domain Eukarya
Kingdom
Fungi
Kingdom
Animalia
Figure 14.25
Evolution Connection:
Rise of the Mammals
 Mass extinctions:


Have repeatedly occurred throughout Earth’s history
Were followed by a period of great evolutionary change
© 2010 Pearson Education, Inc.
 Fossil evidence indicates that:


Mammals first appeared about 180 million years ago
The number of mammalian species
 Remained steady and low in number until about 65 million years
ago and then
 Greatly increased after most of the dinosaurs became extinct
Ancestral
mammal
Extinction of
dinosaurs
Reptilian
ancestor
Monotremes
(5 species)
Marsupials
(324 species)
Eutherians
(5,010 species)
250
65 50
Millions of years ago
200
150
100
0
American black bear
Figure 14.26
Bacteria
Earliest
organisms
Archaea
Eukarya
Figure 14.UN3