Chapter 10: The Origin and
Diversification of Life on Earth
Understanding biodiversity
Lectures by Mark Manteuffel, St. Louis Community College
Learning Objectives
Be able to describe how:

Life on earth most likely originated from nonliving
materials.

Species are the basic units of biodiversity.

Evolutionary trees help us conceptualize and
categorize biodiversity.
Learning Objectives
Be able to describe:
 Macroevolution
 An
and the diversity of life.
overview of the diversity of life on
earth.
10.1 Complex organic
molecules arise in nonliving environments.
Phase 1: The Formation of Small Molecules
Containing Carbon and Hydrogen
The Urey-Miller Experiments
 The
first demonstration that complex
organic molecules could have arisen in
earth’s early environment
Take-home message 10.1
 Under
conditions similar to those on early
earth, small organic molecules form which
have some chemical properties of life.
10.2 Cells and self-replicating
systems evolved together to create
the first life.
Life on earth most likely originated from
nonliving materials.
Enzymes Required
 Phase
2: The formation of self-replicating,
information-containing molecules.
 RNA
 RNA
appears on the scene.
can catalyze reactions necessary for
replication.
The “RNA World” Hypothesis
a
self-replicating system
a
precursor to cellular life?!!
 RNA-based
life and DNA-based life
What Is Life?
 Self-replicating
 How
molecules?
do we define life?!
Life Is Defined by Two
Characteristics
1) the ability to replicate
2) the ability to carry out some sort of
metabolism
Phase 3: The Development of a
Membrane, Enabling Metabolism, and
Creating the First Cells
 Membranes
make numerous aspects of
metabolism possible.
How Did the First Cells Appear?
 Spontaneously?
 Mixtures
of phospholipids
 Microspheres
 Compartmentalization
within cells
Take-home message 10.2
 The
earliest life on earth appeared about
3.5 billion years ago, not long after earth
was formed.
Take-home message 10.2
 Self-replicating
molecules—possibly RNA—
may have formed in earth’s early
environment and later acquired or
developed membranes
 Membranes
enabled these self-replicating
molecules to replicate and make metabolism
possible, the two conditions that define life.
10.3 What is a species?
Biological Species Concept
 Species:
different kinds of organisms
 Species
are natural populations of
organisms that:
• interbreed with each other or could possibly
interbreed
• cannot interbreed with organisms outside
their own group (reproductive isolation)
Two Key Features of the Biological
Species Concept:
1) actually interbreeding
or could possibly
interbreed
2) “natural” populations
Barriers to Reproduction
1) Prezygotic barriers
2) Postzygotic barriers
Prezygotic Barriers
 Make
it impossible for individuals to mate
with each other
or
 Make
it impossible for the male’s
reproductive cell to fertilize the female’s
reproductive cell
These barriers include:
 Courtship
rituals
 Physical
differences
 Physical
or biochemical factors involving
gametes
Postzygotic Barriers
 Occur
after fertilization
 Generally
offspring
 Hybrids
prevent the production of fertile
Take-home message 10.3
Species are generally defined as:
1) populations of individuals that interbreed
with each other or could possibly
interbreed.
2) Species cannot interbreed with organisms
outside their own group.
Take-home message 10.3
 This
concept can be applied easily to most
plants and animals, but for many other
organisms it cannot be applied.
10.4 How do we name species?
We need an organizational system!
Carolus Linnaeus and
Systema Naturae
A scientific name
consists of two parts:
1) genus
2) specific epithet
Hierarchical System
Inclusive categories at
the top…
…leading to more and
more exclusive
categories below.
Take-home message 10.4
 Each
species on earth is given a unique
name, using a hierarchical system of
classification.
 Every
species on earth falls into one of
three domains.
10.5
Species are
not always
easily
defined.
Difficulties in Classifying
Asexual Species
 Doesn’t
involve fertilization or even two
individuals
 Does
not involve any interbreeding
 Reproductive
isolation is not meaningful
Difficulties in Classifying
Fossil Species
 Evidence
for reproductive isolation???
Difficulties in Determining When One
Species Has Changed into Another
 It
may not be possible to identify an exact
point at which the change occurred.
Chihuahuas and Great Danes
generally can’t mate.
Does that mean they are different
species?
Difficulties in Classifying Ring
Species
 Example:
insect-eating songbirds called
greenish warblers
 Unable
to live at the higher elevations of
the Tibetan mountain range
 Live
in a ring around the mountain range
Difficulties in Classifying Ring
Species
 Warblers
interbreed at southern end of ring.
 The
population splits as the warblers move
north along either side of mountain.
 When
the two “side” populations meet at
northern end of ring, they can’t interbreed.
 What
happened?!
Difficulties in Classifying Ring
Species
 Gradual
variation in the warblers on each
side of the mountain range has
accumulated…
 …the
two populations that meet have
become reproductively incompatible…
 …no
exact point at which one species
stops and the other begins
Difficulties in Classifying Hybridizing
Species
 Hybridization
• the interbreeding of closely related species
 Have
 Are
postzygotic barriers evolved?
hybrids fertile?
Morphological Species Concept
 Focus
on aspects of organisms other than
reproductive isolation as defining features
 Characterizes
species based on physical
features such as body size and shape
 Can
be used effectively to classify asexual
species
Take-home message 10.5
 The
biological species concept is useful
when describing most plants and animals.
 It
falls short of representing a universal
and definitive way of distinguishing many
life forms.
Take-home message 10.5
 Difficulties
arise when trying to classify
asexual species, fossil species, speciation
events that have occurred over long
periods of time, ring species, and
hybridizing species.
 In
these cases, alternative approaches to
defining species can be used.
10.6 How do new species arise?
Speciation
 One
species splits into two distinct species.
 Occurs
in two distinct phases
 Requires
more than just evolutionary
change in a population
Allopatric Speciation
 Speciation
with geographic isolation
Speciation without Geographic Isolation
Polyploidy
 Error
during cell division in plants
 Chromosomes
are duplicated but a cell
does not divide.
 This
doubling of the number of sets of
chromosomes is called polyploidy.
Polyploidy
 The
individual with four sets can no longer
interbreed with any individuals having only
two sets of chromosomes
 Self-fertilization
or mating with other
individuals that have four sets can occur.
 Instant
reproductive isolation, considered
a new species.
Take-home message 10.6
 Speciation
is the process by which one
species splits into two distinct species that
are reproductively isolated.
 It
can occur by polyploidy or by a
combination of reproductive isolation and
genetic divergence together.
10.7 The history of life can
be imagined as a tree.
Systematics and Phylogeny
 Systematics
names and arranges species
in a manner that indicated:
• the common ancestors they share
• the points at which they diverged from each
other
Systematics and Phylogeny
 Phylogeny
• evolutionary history, of organisms
 Nodes
• The common ancestor points at which species
diverge
Take-home message 10.7
 The
history of life can be visualized as a
tree; tracing from the branches back
toward the trunk follows the pathway of
descendant back to ancestor.
Take-home message 10.7
 The
tree reveals the evolutionary history
of every species and the sequence of
speciation events that gave rise to them.
10.8 Evolutionary trees show
ancestor-descendant relationships.
Monophyletic Groups
a
group in which all of the individuals are
more closely related to each other than to
any individuals outside of that group
 determined
trees
by looking at the nodes of the
Constructing evolutionary trees
requires comparing similarities and
differences between organisms.
Take-home message 10.8
 Evolutionary
trees constructed by
biologists are hypotheses about the
ancestor-descendant relationships among
species.
Take-home message 10.8
 The
trees represent an attempt to tell us
which groups are most closely related to
which other groups based on physical
features, usually DNA sequences.
10.9 Similar structures don’t
always reveal common ancestry.
The mapping of species’ characteristics
onto phylogenetic trees
 Physical
 DNA
features
sequences
Convergent Evolution
 and
analogous traits
Analogous traits:
Features that are produced by convergent
evolution
Homologous traits:
Features that are inherited from a common
ancestor
How do you know whether traits
are homologous or analogous?
DNA analysis
Take-home message 10.9
 Evolutionary
trees are best constructed by
comparing genetic similarity among
organisms.
 Convergent
evolution can cause distantly
related organisms to appear much more
closely related.
10.10 Macroevolution is
evolution above the species
level.
Short-term and Long-term Results
 Microevolution
 Macroevolution
Take-home message 10.10
 The
process of evolution…
 …in
conjunction with reproductive
isolation…
 …is
sufficient to produce speciation,
diversification, and the rich diversity of life
on earth.
10.11 The pace of
evolution is not constant.
Take-home message 10.11

The pace at which evolution occurs can be
rapid or very slow.

In some cases, the fossil record reveals rapid
periods of evolutionary change punctuated
by longer periods with little change.

In others cases, species may change at a
more gradual, but consistent, pace.
10.12 Adaptive radiations are
times of extreme diversification.
When a small number of species
diversifies into a much larger
number of species
Three Phenomena May Trigger
Adaptive Radiations
 All
result in
access to
plentiful new
resources.
 Colonizers
find a large number of
opportunities for adaptation and
diversification.
 Galapagos finches
 Hawaiian fruit flies
 innovations
such as the wings and rigid
skeleton that appeared in insects
 helped them to diversify into the most
successful group of animals
 more than 800,000 species today!
Take-home message 10.12
Adaptive radiations tend to be triggered by:
1) mass extinctions of potentially
competing species
2) colonization of new habitats
3) the appearance of evolutionary
innovations
10.13 There have been
several mass extinctions on
earth.
Background Extinction
 extinctions
that occur at lower rates
during periods other than periods of mass
extinctions
 occur
mostly as the result of natural
selection
Background and Mass Extinctions
Have Different Causes
 Mass
extinctions are due to extraordinary
and sudden changes to the environment.
 Background
extinctions occur mostly as
the result of natural selection.
Take-home message 10.13
 As
new species are being created, others
are lost through extinction.
 Extinction
may be a consequence of
natural selection or large, sudden changes
in the environment.
Take-home message 10.13
 Mass
extinctions are periods during which
a large number of species on earth
become extinct over a short period of
time.
 These
periods are usually followed by
periods of unusually rapid adaptive
radiations and diversification of the
remaining species.
10.14 All living organisms are
divided into one of three
groups.
Classification Systems
 The
two-kingdom system
• Animal and plant
 The
five-kingdom system
• Monera, plant, animal, fungi, and protists
Classification Takes a Leap Forward
 Carl
Woese, an American biologist, and his
colleagues
 Examined
 Tracking
nucleotide sequences
changes
Woese’s approach is not perfect.
Are viruses alive?
Take-home message 10.14
 All
life on earth can be divided into three
domains—bacteria, archaea, and
eukarya—which reflect their evolutionary
relatedness to each other.
 Plants
and animals are just two of the four
kingdoms in the eukarya domain,
encompassing only a small fraction of the
domain’s diversity.
10.15 The bacteria domain
has tremendous biological
diversity.
Why is morning breath so
stinky?
Bacteria Are a Monophyletic Group
All bacteria have a few features in common:
 single-celled
organisms with no nucleus or
organelles
 one or more circular molecules of DNA
 several methods of exchanging genetic
information
 asexual organisms
Take-home message 10.15
 The
bacteria all share a common ancestor
and have a few features in common:
• All are prokaryotic, asexual, single-celled
organisms with no nucleus or organelles.
• All have one or more circular molecules of
DNA as their genetic material.
• All have several methods of exchanging
genetic information.
Take-home message 10.15
 Bacteria
have evolved a broad diversity of
metabolic and reproductive abilities
relative to Eukarya.
10.16 The archaea domain
includes many species living
in extreme environments.
Several Physical Features Distinguish
Archeans from the Bacteria
 Archaeans’
cell walls contain
polysaccharides not found in either
bacteria or eukaryotes.
 Archeans
have cell membranes,
ribosomes, and some enzymes similar to
those found in eukaryotes.
Take-home message 10.16
 Archaea,
many of which are adapted to
life in extreme environments, physically
resemble bacteria but are more closely
related to eukarya.
Take-home message 10.16
 Because
they thrive in many habitats that
humans have not yet studied well,
including the deepest seas and oceans,
they may turn out to be much more
common than currently believed.
10.17 The eukarya domain
consists of four kingdoms.
Plants, Animals, Fungi, and Protists
Take-home message 10.17
 All
living organisms that you can see with
the naked eye are eukarya, including all
plants, animals, fungi, and protists.
 The
eukarya are unique among the three
domains in that they have cells with
organelles.