Transcript Chapter 10 Part I: The Origin and Diversification of Life on Earth Part I: Sections: 10.1 to 10.

Chapter 10 Part I: The Origin and
Diversification of Life on Earth
Part I:
Sections:
10.1 to 10. 6
10. 15 to 10. 18
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.
 An overview of the diversity of life on earth.
Learning Objectives
 Define life
 Outline the conditions and evidence that support how life on
earth was formed
 Explain how to identify and name a species
 Compare and contrast the biological species concept and the
morphological species concept
 Understand the purpose of a phylogenic tree and what it can
demonstrate
 Define the difference between analogous traits and
homologous features
 Compare and contrast microevolution and macroevolution
 Explain how adaptive radiation and extinction impacts
evolution
 Understand the current biodiversity found in the three
domains
10.1 Complex organic molecules arise in
non-living environments.
Phase 1: The Formation of Small Molecules
Containing Carbon and Hydrogen
Why is it important that Urey and
Miller’s experiment produced amino
acids?
1. Amino acids are the building
blocks of DNA
2. Amino acids are the building
blocks of RNA
3. Amino acids are the building
blocks of protein
4. Amino acids are the building
blocks of triglycerides
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, informationcontaining molecules.
 RNA appears on the scene.
 RNA 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
molecules?
 How 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

Figure 10-4 Are microspheres a key stage in the origin of life?
1.
2.
3.
4.
5.
The basic definition of life is:
the ability to replicate.
the ability to carry out metabolism.
the ability to use oxygen.
the ability to move.
Both 1 and 2.
Take-home message 10.2
The earliest life on earth appeared about 3.5 billion
years ago, not long after earth was formed.
 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 THIS IS HOW WE DO IT
Could life have originated in ice, rather than in
a “warm little pond”?
What if icy baths, not warm ponds, were the
“incubator” of life?
Chemical requirement 1
Precursor molecules need to last a while and need
to come in contact with each other.
Chemical requirement 2
Precursor molecules need to exhibit catalytic
properties.
Is it even feasible that ice was present on early earth and
precursor molecules could have formed in it?
• Intriguing observations and evidence:
– Freeze tubes containing seawater and the building
blocks of RNA; thaw the tubes—find numerous
RNA molecules
– Earth as a “giant snowball”
• Has exploration of the plausibility of ice as the
initial medium of RNA replication answered the
questions about how life on earth originated?
Is there any value to false starts (and even dead
ends) encountered in research investigations?
What feature of ice may have supported precursor molecule
formation on an early earth?
1.
2.
3.
4.
5.
Small compartments form within ice
Ice floats
The temperature of ice is constant
Both 1 and 2.
All of the above.
Take-home message 10.3
• As researchers investigate how life on earth might have
originated, some are questioning the long-held assumptions
that self-replicating molecules with catalytic properties are
most likely to have formed in a warm, wet environment.
• They’ve proposed that the laws of chemistry and the
properties of water as it freezes may actually favor ice as the
initial incubator of life.
• The answer is unclear, but the process of scientific thinking is
guiding investigators to develop and test their hypotheses.
10.3 What is a species?
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)
Biological Species Concept
Species: different kinds of organisms
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
1. Why are horses and zebras considered separate
species?
1. Because their hybrid offspring look strange.
2. Because their hybrid offspring are unhealthy.
3. Because their hybrid offspring would not breed under
natural conditions.
4. All of the above.
2. A “zorse” is sterile,
suggesting what type of
reproductive barrier?
1. Prezygotic
2. Zygotic
3. Postzygotic
4. Embryonic
Postzygotic Barriers
 Occur
after fertilization
 Generally prevent the production of fertile
offspring
 Hybrids
Take-home message 10.4
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.
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.
Which levels of classification do humans share with
zebras?
1. Family and Genus
2. Genus and Species
3. Class, Order, and Family
4. Kingdom, Phylum, and Class
5. Kingdom, Phylum, Class, Order, and Family
Take-home message 10.5
 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.
10.6 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
 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 Hybridizing
Species
 Hybridization
• the interbreeding of closely related species
 Have
postzygotic barriers evolved?
 Are hybrids fertile?
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
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?!
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
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
Which organism below is not easily classified using the
biological species concept?
1. Bacterial cell
2. Fossil
3. Greenish warblers
4. Fertile hybrids
5. All of the above.
Which choice below would require the morphological species concept to
delineate between the two species?
1. Dog and cat.
2. Salmonella and E. coli
3. Cow and goat.
4. Donkey and horse
Take-home message 10.6
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.
 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.

10.15 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 nucleotide sequences
 Tracking changes
Woese’s approach is not perfect.

Are viruses alive?
According to the phylogenetic tree below, which of
the following are most closely related?
1.
2.
3.
4.
Bacteria and archaea
Archaea and protists
Fungi and animals
Bacteria and animals
Take-home message 10.15
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.

10.16 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 10.16
 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.
• Bacteria have evolved a broad diversity of metabolic and
reproductive abilities relative to Eukarya.
10.17 The archaea domain includes many
species living in extreme environments.
Several Physical Features Distinguish Archeans
from the Bacteria
Thermophiles
 Halophiles
 High- and low-pH tolerant
 High-pressure tolerant
 Methanogens

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 10.17
Archaea, many of which are adapted to life in extreme
environments, physically resemble bacteria but are
more closely related to eukarya.
 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.

10.18 The eukarya domain consists of four
kingdoms.
Protists,
Plants,
Fungi, and Animals,
Take-home message 10.18
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.
