the diversity of life on earth

Day 17 November 4th Chapter 10 - The Origin and Diversification of Life on Earth

Dr. Amy B HollingsworthThe University of Akron

Fall 2014

Chapter 10: The Origin and Diversification of Life on Earth

Understanding biodiversityLectures by Mark Manteuffel, St. Louis Community College

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.

Be able to describe:

Macroevolution and the diversity of life.

An overview of the diversity of life on earth.

10.1–10.2

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 Experiments

The first demonstration that complex organic molecules could have arisen in earth’s early environment

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.

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

10.3–10.6

Species are the

basic units of

biodiversity.

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 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

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. Genus2. Specific epithet

Hierarchical System

Inclusive categories at the top…

…leading to more and more exclusive categories below

10.5 Species are not always easily defined.

Difficulties in Classifying Asexual Species

Does not involve fertilization or even two individuals

Does not involve any interbreeding

Reproductive isolation that 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 the northern end of the 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.

There is 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

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

10.7–10.9

Evolutionary trees

help us

conceptualize and

categorize

biodiversity.

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

10.8 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 requires comparing similarities and differences between organisms.