Transcript Unit 1 Ch. 1, 17, 18. WHAT IS BIOLOGY?

Chapter 14
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.


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”
• The biological species concept is problematic for:




Asexual organisms. Why?
Fossil organisms. Why?
Dead animals in alcohol in jars. Why?
And sometimes animals in captivity. Why?
What Is a Species?
Figure 14.2
Similarity between different species
Diversity within one species
• Eastern and western meadowlarks appear similar in appearance but
are reproductively isolated. Humans are all one species (Homo
sapiens) and are all potentially interbreeding.
• What do “reproductively isolated” and “potentially interbreeding” mean?

Speciation:
• Is the focal point of macroevolution
• May occur based on two contrasting patterns, nonbranching 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. Why?

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
Reproductive Barriers/Isolating Mechanisms
between Species


What’s the logic of isolating mechanisms and
reproductive barriers?
I.e., Why is interspecific breeding biologically “stupid?”
?
Consider the three-toed tree squab and
the three-toed grass squab of Borneo
I made that up but let’s pretend…

What’s the “penalty for inter-squab promiscuity?
Reproductive Barriers
aka
Isolating Mechanisms
 Prezygotic
barriers prevent hybridization in
the first place.
(“Just say no!”)
 Postzygotic
barriers work after fertilization
and make survival of the hybrid less likely.
(“Well, that was a waste of time and effort!”)
Reproductive Barriers between Species

Prezygotic barriers prevent mating or
fertilization between species.
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
PREZYGOTIC BARRIERS
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Gametic isolation particularly important when fertilization is external

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
Hybrid Breakdown
Horse
Donkey
Offspring are frail and less
viable
Mule
These rice hybrids are fertile
but next generation is sterile
and small.
Offspring sterile, infertile
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
Sympatric speciation
Figure 14.6
Allopatric Speciation

Geologic processes can:
• Fragment a population into two or more isolated populations
• Contribute to allopatric speciation

The antelope squirrels of the Grand Canyon Rim
• Ammospermophilus harrisii (south rim)
• Ammospermophilus leucuris (north rim)
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 sympatric
Populations
become allopatric
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)
Polyploidy
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 fetusChimpanzee 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
Radioactive decay
of carbon-14
Carbon-14 radioactivity
(as % of living organism’s
C-14 to C-12 ratio)
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
Eurasia
65
Africa
South
America
India
Madagascar
Antarctica
Paleozoic
251 million years ago
Mesozoic
135
Laurasia
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
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
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
Carnivora
Family Genus Species
Panthera
Felidae Panthera
pardus
(leopard)
Mephitis
Mephitis mephitis
Mustelidae
(striped skunk)
Lutra
Lutra lutra
(European
otter)
Canis
latrans
Canidae Canis (coyote)
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
Molecular Biology as a Tool in
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
Long gestation
Kangaroo
Beaver
Figure 14.23
Ingroup
(mammal

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
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
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
Monotremes
(5 species)
Extinction of
dinosaurs
Reptilian
ancestor
Marsupials
(324 species)
Eutherians
(5,010 species)
250
200
150
Millions of years ago
100
65 50
0
American black bear
Figure 14.26
Bacteria
Earliest
organisms
Archaea
Eukarya
Figure 14.UN3
End for Exam 1