Chapter 10: The Origin and Diversification of Life on Earth Understanding biodiversity Lectures by Mark Manteuffel, St. Louis Community College.

Chapter 10: The Origin and Diversification of Life on

Earth

Understanding biodiversityLectures 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 and the diversity of life.

An overview of the diversity of life on earth.

Life on earth most likely originated from non-living

materials.

10.1 Complex organic molecules arise in non-living environments.

Phase 1: The Formation of Small Molecules Containing Carbon and

Hydrogen

The Urey-Miller Experiment

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 can form, and these molecules have some chemical properties of life.

Life on earth most likely originated from nonliving materials.

10.2 Cells and self-replicating systems evolved together to create the first life.

Enzymes Required

Phase 2: The formation of self-replicating, information-containing molecules.

RNA appears on the scene.

RNA can catalyze reactions necessary for replication.

What Is Life?

The ability to replicateSelf-replicating molecules?

The ability to carry out metabolismDevelopment of a membrane?

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


The earliest life on earth, which resembled bacteria, appeared about 3.5 billion years ago, not long after earth was formed.


Evidence supports the idea that self-replicating molecules, possibly RNAs, may have formed in earth’s early environment and later acquired or developed membranes…

…enabling them to replicate and making 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?


• 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.

Species are the basic units ofbiodiversity.

10.4 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 Reproduction1) Prezygotic barriers2) Postzygotic barriers

Prezygotic Barriers

Make it impossible for individuals to mate with each otheror

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 prevent the production of fertile offspring

Hybrids


Species are generally defined as: 1) populations of individuals that

interbreed with each other, or could possibly interbreed….

2) …and that cannot interbreed with organisms from other such groups.


This concept can be applied easily to most plants and animals, but is not applicable for many other types of organisms.

10.5 How do we name species?

We need an organizational system!

Carolus Linnaeus and Systema Naturae

A scientific name consists of two parts:1) genus2) specific epithet

Hierarchical System

Inclusive categories at the top…

…leading to more and more exclusive categories below.


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

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 ClassifyingRing 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 postzygotic barriers evolved?

Are 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


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, species arising over long periods of time, ring species, and hybridizing species.

In these cases, alternative approaches to defining species can be used.

10.7 How do new species arise?

Speciation

One species splits into two distinct species.

Occurs in two distinct phases:Reproductive isolationGenetic divergence

Requires more than just evolutionary change in a population

Allopatric Speciation

Speciation with geographic isolation

Q Could you create a new species in the laboratory?

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.


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.

Evolutionary trees help us conceptualize and categorize

biodiversity.

10.8 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

Phylogeny• evolutionary history, of organisms


The history of life can be visualized as a tree; by tracing from the branches back toward the trunk, we can follow the pathway back from descendants to their ancestors.


The tree reveals the evolutionary history of all species and the sequence of speciation events that gave rise to them.

10.9 Evolutionary trees show ancestor-descendant relationships.

• Are humans more advanced, evolutionarily, than cockroaches?

• Can bacteria be considered “lower” organisms?

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 by looking at the nodes of the trees

Constructing evolutionary trees by comparing similarities and differences among organisms.


Evolutionary trees constructed by biologists are hypotheses about the ancestor-descendant relationships among species.


The trees represent an attempt to describe which groups are most closely related to which other groups.

10.10 Similar structures don’t always reveal common ancestry.

The mapping of species’ characteristics onto phylogenetic trees

Physical features

DNA 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


Evolutionary trees are best constructed by comparing organisms’ DNA sequences rather than comparing physical similarities

• Convergent evolution can cause distantly related organisms to appear closely related, but it doesn’t increase their DNA sequence similarity.

Macroevolution gives rise to great diversity.

10.11 Macroevolution is evolution above the species level.

Short-term and Long-term Results

Microevolution

Macroevolution


The process of evolution…

…in conjunction with reproductive isolation…

…is sufficient to produce speciation and the rich diversity of life on earth.

10.12 The pace of evolution is not constant.


The pace at which evolution occurs can be rapid or very slow.

In some cases, the fossil record reveals long periods with little evolutionary change punctuated by rapid periods of change.

In others cases, species may change at a more gradual but consistent pace.

10.13 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!


Adaptive radiations tend to be triggered by:

1) mass extinctions of potentially competing species

2) colonization of new habitats

3) or the appearance of evolutionary innovations

10.14 There have been several mass extinctions on earth.

“Forests keep disappearing, rivers dry up, wild life’s become extinct, the climate’s ruined and the land grows poorer and uglier every day.”— ANTON CHEKHOV, Uncle Vanya, 1899

Background Extinction

extinctions that occur at lower rates during periods other than periods of mass extinctions

occur mostly as the result of natural selection

Mass Extinction

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.


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.


Mass extinctions are periods during which a large number of species on earth become extinct over a short period of time.

An overview of the diversity of life on earth: organisms are divided into three domains.

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?


All life on earth can be divided into three domains—bacteria, archaea, and eukarya—which reflect species’ 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


All bacteria 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 a much broader diversity of metabolic and reproductive abilities than do the eukarya.

10.17 The archaea domain includes many species living in extreme environments.

The archaea exhibit tremendous diversity and are often divided into five groups based on their physiological features

Thermophiles

Halophiles

High- and low-pH tolerant

High-pressure tolerant

Methanogens


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.

Plants, Animals, Fungi, and Protists


All living organisms that we can see with the naked eye (and many that are too small to be seen) are eukarya, including all plants, animals, fungi, and protists.

The eukarya are unique among the three domains in that they have cells with organelles.

Chapter 10: The Origin and Diversification of Life on Earth Understanding biodiversity Lectures by Mark Manteuffel, St. Louis Community College.

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