Transcript The Origin and Diversification of Life on Earth

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:
Biodiversity leads to long-term stability in an
ecosystem.
 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.

Why do we care about biological diversity?
• Diversity-stability hypothesis proposes that an
ecosystem with high biodiversity is better able
to survive disturbances than an ecosystem with
low biodiversity.
• Other benefits?
–
–
–
–
Plants/producers
Medicines
Foods
Fibers/products
10.1 Complex organic
molecules arise in nonliving environments.
The 4-Stage Hypothesis for the Origin of Life
explains the origin of organic molecules and
how cooperation and polymerization led to the
evolution of the first prokaryotic cell.
Follow the slides – your book doesn’t cover
Stage 2: Abiotic Synthesis of Organic
Polymers
Stage 1: The Formation of Small Molecules
Containing Carbon and Hydrogen
The Urey-Miller Experiments
 Stage
1: Abiotic Synthesis of Organic
Monomers (small molecules containing
carbon and hydrogen)
 The first demonstration that complex
organic molecules could have arisen in
earth’s early environment
– Recall repeatability in science
– These experiments have been repeated again
and again and have produced all 20 amino
acids, several sugars, lipids, and nucleotides.
Stage 2: Abiotic Synthesis of
Organic Polymers
• Researchers have observed polymerization
of organic monomers in various situations.
• By dripping solutions of organic monomers
onto hot sand or rock, the heat vaporizes
the water and concentrates the monomers.
• Some of the monomers spontaneously
bond together via dehydration synthesis
without the aid of enzymes or other cellular
equipment.
10.2 Cells and self-replicating
systems evolved together to create
the first life.
RNA appears on the scene.
RNA can catalyze reactions necessary for
replication.
Here it gets a little more speculative.
Some researchers believe enzymes were
required.
Stage 3: Origin of Self-Replicating
Molecules
• Laboratory experiments have shown that short
RNA molecules can assemble spontaneously.
Original “gene”
RNA monomers
Formation of
short RNA
polymers: simple
“genes”
Assembly of a
complementary
RNA chain
(pairing rules are
G with C and A
with U)
Complementary
chain serves as
template for
making
copy of original
“gene”
Stage 4: The Development of a
Membrane, Enabling Metabolism, and
Creating the First Cells
 Membranes
numerous
aspects of
metabolism
possible.
make
Lipids self-assemble into
membrane enclosed droplets.
10.3 What is a species?
Species is a Latin word meaning “kind”
or “appearance”, but many times we
cannot tell simply by appearance alone.
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 – before the mating
attempt
or
 Make
it impossible for the male’s
reproductive cell to fertilize the female’s
reproductive cell – after the mating
attempt
Prezygotic barriers include:
 Courtship
rituals – behavioral isolation
 Physical
differences – habitat isolation,
temporal isolation, and mechanical
isolation
 Physical
or biochemical factors involving
gametes – gametic isolation
Mating behaviors may be complex… slug sex video?
Postzygotic Barriers
 Occur
after fertilization
– Are backup mechanisms that operate should
interspecies mating actually occur and
produce hybrid zygotes
– Offspring fail to develop normally
– Prevent the production of fertile offspring
 Hybrids
• Postzygotic barriers include:
– Hybrid inviability = offspring die before they
can reproduce.
– Hybrid sterility = The mule is sterile.
Horse
Mule (hybrid)
Donkey
Figure 14.7
10.4 How do we
name species?
A scientific name for a
particular species
consists of two parts
(binomial
nomenclature):
1) genus
2) specific epithet
(species name)
Hierarchical System
Inclusive categories at
the top…
…leading to more and
more exclusive
categories below.
10.5
Species are
not always
easily
defined
using the
biological
species
concept.
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
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.
Asexual
reproduction
and selffertilization
are much
more
common in
plants.
10.7 The history of life can
be imagined as a tree.
The tree reveals the
evolutionary history
of every species and
the sequence of
speciation events
that gave rise to
them.
 This tree is only a
working hypothesis
and is revised as
new evidence is
revealed.

Most evolutionary trees are constructed
using fossil, structural, and more and
more molecular evidence.
10.9 Similar
structures
don’t always
reveal
common
ancestry.
Recall analogous
vs. homologous
structures
Because
appearances
are
sometimes
deceptive,
molecular
evidence is
generally
more reliable.
10.10 Macroevolution is
evolution that goes beyond
the species level.
Short-term and Long-term Results
 Microevolution
 Macroevolution
10.11 The pace of evolution is not
constant.
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.
Evolutionary Innovations
• What accounts for the
evolution of biological
novelty like flight in
birds and human
intelligence?
Birds are derived from a
lineage of earthbound
reptiles.
Developed from flightless
ancestors, but how?
• Exaptation
– Involves a structure that evolves in one context
and gradually becomes adapted for other
functions.
– Is one mechanism for novel features to arise
gradually.
– Natural selection can only refine a structure in the
context of its current utility, it does not predict
future change.
– In birds, did feathers or lightweight bones come first? The
first flights may have been glides or extended hops.
Feathers are also used for warmth.
Evolutionary Innovations
• A subtle change in developmental genes can
have profound effects.
• Paedomorphosis
– Is the retention
of juvenile body
features in the
adult
– Probably played
a role in human
evolution
Neoteny: Human and Chimpanzee skull
development:
Chimpanzee fetus
Chimpanzee adult
Extending the juvenile process of brain development helps
the human brain grow larger .
Human fetus
Human adult
Figure 14.17
• Earth was born 4.5 billion years ago
– Prokaryotes - 3.5
billion years ago
– Oxygen production 2.5 billion years ago
– Single-celled
eukaryotic organisms
- 1.7 billion years ago
– Multicellular
organisms – 1 billion
years
– Animal diversification
– 570 million
– Plants and fungi move
to land – 475 million
10.14 All living organisms are
divided into one of three groups.
10.15 The bacteria domain has tremendous
biological diversity.
10.16 The archaea domain includes many
species living in extreme environments.
10.17 The eukarya domain consists
of four kingdoms.