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.

The oldest rocks, found in Greenland, are about 3.8 billion years old. The earliest life forms appeared not long after these rocks were formed: fossilized bacteria-like cells have been found in rocks that are 3.4 billion years old.

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

In 2008, they discovered all 20 amino acids present in the experiment.

Began producing the ozone layer

Life on earth most likely originated from nonliving materials.

After the generation of numerous organic molecules such as amino acids, the second phase in the generation of life from non-life was probably the assembly of these building block molecules into self-replicating, information-containing molecules.

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 – form spherical units that may have been first cells

Microspheres

Compartmentalization within cells

10.3–10.6

Species are the

basic units of

biodiversity.

10.3 What is a species?

How do we know when to classify two individuals as members of different groups and when to classify them as two individuals who are members of the same group?

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???

When it comes to classifying fossil species, differences in the sizes and shapes of fossil bones can never reveal definitively whether there was reproductive isolation between the individuals from whom the bones came. This makes it impossible to apply the biological species concept.

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.

Based on fossils, it appears that modern-day humans, Homo sapiens, evolved from a related species called Homo erectus about 250,000 to 400,000 years ago. This seems reasonable until you consider that your parents—who are in the species Homo sapiens—were born to your Homo sapiens grandparent who were born to your Homo sapiens great grandparents, and so on. If humans evolved from Homo erectus, at what exact point did H. erectus turn into H. sapiens? 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?

Biologists don’t really have a clue about how many species there are on earth. Estimates of the number vary tremendously, from low estimates of 5 million to high estimates of 100 million. Biologists do, however, know the process by which they all arose.

Speciation

One species splits into two distinct species.

Occurs in two distinct phases

Requires more than just evolutionary change in a population

Speciation without Geographic Isolation

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.