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Chapter 26
The Tree of Life:
An Introduction to
Biological Diversity
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Changing Life on a Changing Earth
• Life is a continuum extending from the earliest
organisms to the variety of species that exist today
• Geological events change the course of evolution
• Conversely, life changes the planet that it inhabits
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 26.1: Conditions on early Earth made the
origin of life possible
• Chemical and physical processes on early Earth
may have produced very simple cells through a
sequence of stages:
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into polymers
3. Packaging of molecules into “protobionts”
4. Origin of self-replicating molecules
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Synthesis of Organic Compounds on Early Earth
• Earth formed about 4.6 billion years ago, along
with the rest of the solar system
• Earth’s early atmosphere contained water vapor
and chemicals released by volcanic eruptions
• Experiments simulating an early Earth atmosphere
produced organic molecules from inorganic
precursors, but such an atmosphere on early
Earth is unlikely
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 26-2
CH4
Miller-Urey
Experiment
Water vapor
Electrode
Condenser
Cold
water
H2O
Cooled water
containing
organic
molecules
Sample for
chemical analysis
• Instead of forming in the atmosphere, the first
organic compounds may have been synthesized
near submerged volcanoes and deep-sea vents
• Bubble Model
Video: Hydrothermal Vent
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Video: Tubeworms
Extraterrestrial Sources of Organic Compounds
• Some organic compounds from which the first life
on Earth arose may have come from space
• Carbon compounds have been found in some
meteorites that landed on Earth
• Small organic molecules polymerize when they
are concentrated on hot sand, clay, or rock
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Protobionts
• Protobionts are aggregates of abiotically
produced molecules surrounded by a membrane
or membrane-like structure
– Could have formed spontaneously
– liposomes can form when lipids or other
organic molecules are added to water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 26-4
Glucose-phosphate
20 mm
Glucose-phosphate
Phosphorylase
Starch
Amylase
Phosphate
Maltose
Maltose
Simple reproduction
Simple metabolism
The “RNA World” and the Dawn of Natural Selection
• The first genetic material was probably RNA, not
DNA
• RNA molecules called ribozymes have been found
to catalyze many different reactions, including:
– Self-splicing
– Making complementary copies of short
stretches of their own sequence or other short
pieces of RNA
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Early protobionts with self-replicating, catalytic
RNA would have been more effective at using
resources and would have increased in number
through natural selection
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fossil Record and Dating
• The absolute ages of fossils can be determined by
radiometric dating – radioactive isotopes
• The magnetism of rocks can provide dating
information
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ratio of parent isotope
to daughter isotope
LE 26-7
Accumulating
“daughter”
isotope
1
2
Remaining
“parent”
isotope
1
1
4
1
2
Time (half-lives)
3
8
1
4
16
• The geologic record is divided into three eons: the
Archaean, the Proterozoic, and the Phanerozoic
• The Phanerozoic eon is divided into three eras:
the Paleozoic, Mesozoic, and Cenozoic
• Each era is a distinct age in the history of Earth
and its life, with boundaries marked by mass
extinctions seen in the fossil record
• Lesser extinctions mark boundaries of many
periods within each era
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Mass Extinctions
• The fossil record chronicles a number of
occasions when global environmental changes
were so rapid and disruptive that a majority of
species were swept away
• Provides evidence for punctuated equilibrium
rather than gradualism in evolution
Animation: The Geologic Record
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 26-8
600
Millions of years ago
400
300
200
500
100
0
100
2,500
80
Number of
taxonomic
families
Permian mass
extinction
2,000
Extinction rate
60
1,500
40
Cretaceous
mass extinction
20
1,000
Paleozoic
Mesozoic
Cenozoic
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
0
Permian
Devonian
Silurian
Ordovician
Cambrian
Proterozoic eon
0
Carboniferous
500
• The Permian extinction killed about 96% of
marine animal species and 8 out of 27 orders of
insects
• It may have been caused by volcanic eruptions
• The Cretaceous extinction doomed many marine
and terrestrial organisms, notably the dinosaurs
• It may have been caused by a large meteor
impact
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Mass extinctions
– opportunities for adaptive radiations into newly
vacated ecological niches
• Drastic change in the environment would provide
a lot of NATURAL SELECTION
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 26.3: As prokaryotes evolved, they
exploited and changed young Earth
• The oldest known fossils are stromatolites,
rocklike structures composed of many layers of
bacteria and sediment
• Stromatolites date back 3.5 billion years ago
• Prokaryotes were Earth’s sole inhabitants from 3.5
to about 2 billion years ago
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Electron Transport Systems
• Electron transport systems were essential to early
life
• Some of their aspects may precede life itself
• The earliest types of photosynthesis did not
produce oxygen
• Oxygenic photosynthesis probably evolved
about 3.5 billion years ago in cyanobacteria
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Effects of oxygen accumulation in the
atmosphere about 2.7 billion years ago:
– Posed a challenge for life
– Provided opportunity to gain energy from light
– Allowed organisms to exploit new ecosystems
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 26.4: Eukaryotic cells arose from symbioses
and genetic exchanges between prokaryotes
• Among the most fundamental questions in biology
is how complex eukaryotic cells evolved from
much simpler prokaryotic cells
• ENDOSYMBIOTIC THEORY
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Endosymbiotic Origin of Mitochondria and Plastids
• mitochondria and plastids were formerly small
prokaryotes living within larger host cells
• Mito and plastids started as undigested prey or
internal parasites
• In the process of becoming more interdependent,
the host and endosymbionts would have become
a single organism
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 26-13
Cytoplasm
DNA
Plasma
membrane
Ancestral
prokaryote
Infolding of
plasma membrane
Endoplasmic reticulum
Nuclear envelope
Nucleus
Engulfing of aerobic
heterotrophic
prokaryote
Cell with nucleus
and endomembrane
system
Mitochondrion
Mitochondrion
Ancestral
heterotrophic
eukaryote
Engulfing of
photosynthetic
prokaryote in
some cells
Plastid
Ancestral
photosynthetic eukaryote
• Key evidence supporting an endosymbiotic origin
of mitochondria and plastids:
– Similarities in inner membrane structures and
functions
– Both have their own circular DNA
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Eukaryotic Cells as Genetic Chimeras
• Endosymbiotic events and horizontal gene
transfers may have contributed to the large
genomes and complex cellular structures of
eukaryotic cells
• Eukaryotic flagella and cilia may have evolved
from symbiotic bacteria, based on symbiotic
relationships between some bacteria and
protozoans
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 26-14
50 mm
Concept 26.5: Multicellularity evolved several
times in eukaryotes
• After the first eukaryotes evolved, a great range of
unicellular forms evolved
• Multicellular forms evolved also
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Earliest Multicellular Eukaryotes
• Molecular clocks date the common ancestor of
multicellular eukaryotes to 1.5 billion years
• The oldest known fossils of eukaryotes are of
relatively small algae that lived about 1.2 billion
years ago
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Larger organisms do not appear in the fossil
record until several hundred million years later
• Chinese paleontologists recently described 570million-year-old fossils that are probably animal
embryos
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 26-15
150 mm
Two-celled stage of embryonic
development (SEM)
200 mm
Later embryonic stage
(SEM)
The Colonial Connection
• The first multicellular organisms were colonies,
collections of autonomously replicating cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Some cells in the colonies became specialized for
different functions
• The first cellular specializations had already
appeared in the prokaryotic world
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The “Cambrian Explosion”
• Most of the major phyla of animals appear in the
fossil record of the first 20 million years of the
Cambrian period
• Two animal phyla, Cnidaria and Porifera, are
somewhat older, dating from the late Proterozoic
• Molecular evidence suggests that many animal
phyla originated and began to diverge much
earlier, between 1 billion and 700 million years ago
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Early
Paleozoic
era
(Cambrian
period)
Late
Proterozoic
eon
Millions of years ago
500
542
Arthropods
Molluscs
Annelids
Brachiopods
Chordates
Echinoderms
Cnidarians
Sponges
LE 26-17
Colonization of Land by Plants, Fungi, and Animals
• Plants, fungi, and animals colonized land about
500 million years ago
• Symbiotic relationships between plants and fungi
are common today and date from this time
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Continental Drift
• The continents drift across our planet’s surface on
great plates of crust that float on the hot
underlying mantle
• These plates often slide along the boundary of
other plates, pulling apart or pushing each other
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 26.6: New information has revised our
understanding of the tree of life
• Molecular data have provided insights into the
deepest branches of the tree of life
• Early classification systems had two kingdoms:
plants and animals
• Robert Whittaker proposed five kingdoms:
Monera, Protista, Plantae, Fungi, and Animalia
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 26-21
Plantae
Fungi
Protista
Monera
Animalia
Reconstructing the Tree of Life: A Work in Progress
• The five kingdom system has been replaced by
three domains: Archaea, Bacteria, and Eukarya
• Each domain has been split into kingdoms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Domain Archaea
Domain Bacteria
Universal ancestor
Domain Eukarya
Charophyceans
Chlorophytes
Red algae
Cercozoans, radiolarians
Chapter 27
Stramenopiles (water molds, diatoms, golden algae, brown algae)
Alveolates (dinoflagellates, apicomplexans, ciliates)
Euglenozoans
Diplomonads, parabasalids
Euryarchaeotes, crenarchaeotes, nanoarchaeotes
Korarchaeotes
Gram-positive bacteria
Cyanobacteria
Spirochetes
Chlamydias
Proteobacteria
LE 26-22a
Chapter 28
Plants
Fungi
Animals
Bilaterally symmetrical animals (annelids,
arthropods, molluscs, echinoderms, vertebrates)
Chapter 32
Cnidarians (jellies, coral)
Sponges
Chapter 31
Choanoflagellates
Club fungi
Sac fungi
Chapter 28
Arbuscular mycorrhizal fungi
Zygote fungi
Chytrids
Chapter 30
Amoebozoans (amoebas, slime molds)
Angiosperms
Chapter 29
Gymnosperms
Seedless vascular plants (ferns)
Bryophytes (mosses, liverworts, hornworts)
LE 26-22b
Chapters 33, 34