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Chapters 25 and 26: history and diversity of life on Earth. Ch. 25: History of Life on Earth. Figure 25.1. How do we know so much about dinosaurs? What can we tell about them?. Figure 25.UN01. Cryolophosaurus skull. Concept 25.1: Conditions on early Earth made the origin of life possible.

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Figure 25 1
Figure 25.1

How do we know so much about dinosaurs? What can we tell about them?


Figure 25 un01
Figure 25.UN01

Cryolophosaurus skull


Concept 25 1 conditions on early earth made the origin of life possible
Concept 25.1: 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 macromolecules

3. Packaging of molecules into protocells

4. Origin of self-replicating molecules

© 2011 Pearson Education, Inc.


Synthesis of organic compounds on early earth
Synthesis of Organic Compounds on Early Earth life possible

Earth formed about 4.6 billion years ago, along with the rest of the solar system

Bombardment of Earth by rocks and ice likely vaporized water and prevented seas from forming before 4.2 to 3.9 billion years ago

Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

© 2011 Pearson Education, Inc.


In the 1920s, A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment and could produce organics

In 1953, Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules (amino acids) in a reducing atmosphere is possible

© 2011 Pearson Education, Inc.


Amino acids have also been found in meteorites that the early atmosphere was a reducing environment and could produce organics

© 2011 Pearson Education, Inc.

The key builiding blocks of life are not hard to come by

  • RNA monomers have been produced spontaneously from simple molecules

  • In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer

  • Adding clay can increase the rate of vesicle formation

  • Vesicles exhibit simple reproduction and metabolism and maintain an internal chemical environment

    • Resultprotocells


Figure 25 3
Figure 25.3 that the early atmosphere was a reducing environment and could produce organics

0.4

Precursor molecules plus

montmorillonite clay

Relative turbidity,

an index of vesicle number

0.2

Precursor

molecules only

0

40

60

0

20

Time (minutes)

(a) Self-assembly

1 m

Vesicle

boundary

20 m

(b) Reproduction

(c) Absorption of RNA


Self replicating rna and the dawn of natural selection
Self-Replicating RNA and the that the early atmosphere was a reducing environment and could produce organicsDawn of Natural Selection

The first genetic material was probably RNA, not DNA

RNA molecules called ribozymes have been found to catalyze many different reactions

For example, ribozymes can make complementary copies of short stretches of RNA

© 2011 Pearson Education, Inc.


Concept 25 2 the fossil record documents the history of life
Concept 25.2: The fossil record documents the history of life

The fossil record reveals changes in the history of life on Earth

© 2011 Pearson Education, Inc.


© 2011 Pearson Education, Inc. life

Video: Grand Canyon


Figure 25 4
Figure 25.4 life

Present

Dimetrodon

Rhomaleosaurus

victor

100 mya

1 m

175

Tiktaalik

0.5 m

200

270

300

4.5 cm

Hallucigenia

Coccosteus

cuspidatus

375

400

1 cm

Dickinsonia

costata

500

525

2.5 cm

Stromatolites

565

600

1,500

Fossilized

stromatolite

3,500

Tappania


Few individuals have fossilized, and even fewer have been discovered

The fossil record is biased in favor of species that

Existed for a long time

Were abundant and widespread

Had hard parts

© 2011 Pearson Education, Inc.


How rocks and fossils are dated
How Rocks and Fossils Are Dated discovered

Sedimentary strata reveal the relative ages of fossils

The absolute ages of fossils can be determined by radiometric dating

A “parent” isotope decays to a “daughter” isotope at a constant rate

Each isotope has a known half-life, the time required for half the parent isotope to decay

© 2011 Pearson Education, Inc.


Figure 25 5
Figure 25.5 discovered

Accumulating

“daughter”

isotope

Fraction of parent

isotope remaining

1

2

Remaining

“parent”

isotope

1

4

1

8

1

16

1 2 3 4

Time (half-lives)


Radiocarbon dating can be used to date fossils up to 75,000 years old

For older fossils, some isotopes can be used to date sedimentary rock layers above and below the fossil

© 2011 Pearson Education, Inc.


The origin of new groups of organisms
The Origin of New Groups of Organisms years old

Mammals belong to the group of animals called tetrapods

The evolution of unique mammalian features can be traced through gradual changes over time

© 2011 Pearson Education, Inc.


Figure 25 6
Figure 25.6 years old

Key to skull bones

Reptiles

(including

dinosaurs and birds)

Articular

Dentary

Quadrate

Squamosal

OTHER

TETRA-

PODS

†Dimetrodon

Synapsids

†Very late (non-

mammalian)

cynodonts

Early cynodont (260 mya)

Therapsids

Cynodonts

Temporal

fenestra

(partial view)

Mammals

Synapsid (300 mya)

Hinge

Later cynodont (220 mya)

Temporal

fenestra

Hinges

Hinge

Therapsid (280 mya)

Very late cynodont (195 mya)

Temporal

fenestra

Hinge

Hinge


The years oldgeologic record is divided into the Archaean, the Proterozoic, and the Phanerozoic eons

The Phanerozoic encompasses multicellular eukaryotic life

The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic

Concept 25.3: Key events in life’s history include the origins of single-celled and multicelled organisms and the colonization of land

© 2011 Pearson Education, Inc.


Table 25 1
Table 25.1 years old


Figure 25 7 1
Figure 25.7-1 years old

Origin of solar

system and

Earth

4

Archaean

B

o

i

g

l

l

a

i

o

s

n

r

s

a

e

of

y

3

Prokaryotes

Atmospheric oxygen


Figure 25 7 2
Figure 25.7-2 years old

Origin of solar

system and

Earth

Animals

Multicellular

eukaryotes

4

1

Proterozoic

Archaean

B

o

i

g

l

l

a

i

o

s

n

r

s

a

e

of

y

2

3

Prokaryotes

Single-celled

eukaryotes

Atmospheric oxygen


Figure 25 7 3
Figure 25.7-3 years old

Meso-

zoic

Cenozoic

Humans

Paleozoic

Colonization

of land

Origin of solar

system and

Earth

Animals

Multicellular

eukaryotes

4

1

Proterozoic

Archaean

B

o

i

g

l

l

a

i

o

s

n

r

s

a

e

of

y

2

3

Prokaryotes

Single-celled

eukaryotes

Atmospheric oxygen


Photosynthesis and the oxygen revolution
Photosynthesis and the Oxygen Revolution years old

Most atmospheric oxygen (O2) is of biological origin

In the search for extraterrestrial life, it is our primary target of observation

© 2011 Pearson Education, Inc.


Figure 25 8
Figure 25.8 years old

1,000

100

10

1

Atmospheric O2

(percent of present-day levels; log scale)

0.1

“Oxygen

revolution”

0.01

0.001

0.0001

4 3 2 1 0

Time (billions of years ago)


The early rise in O years old2 was likely caused by ancient cyanobacteria

A later increase in the rise of O2 might have been caused by the evolution of eukaryotic cells containing chloroplasts

© 2011 Pearson Education, Inc.


The first eukaryotes
The First Eukaryotes years old

Eukaryotic cells have a nuclear envelope, mitochondria, endoplasmic reticulum, and a cytoskeleton

The oldest fossils of eukaryotic cells date back 2.1 billion years

The endosymbiont theory proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells

An endosymbiont is a cell that lives within a host cell

© 2011 Pearson Education, Inc.


Which was the first endsymbiotic component
Which was the first endsymbiotic component, years old

chloroplasts or mitochondria?


Figure 25 9 1
Figure 25.9-1 years old

Plasma membrane

Cytoplasm

DNA

Ancestral

prokaryote

Nucleus

Endoplasmic

reticulum

Nuclear envelope


Figure 25 9 2
Figure 25.9-2 years old

Plasma membrane

Cytoplasm

DNA

Ancestral

prokaryote

Nucleus

Endoplasmic

reticulum

Nuclear envelope

Aerobic heterotrophic

prokaryote

Mitochondrion

Ancestral

heterotrophic eukaryote


Figure 25 9 3
Figure 25.9-3 years old

Plasma membrane

Cytoplasm

DNA

Ancestral

prokaryote

Nucleus

Endoplasmic

reticulum

Photosynthetic

prokaryote

Mitochondrion

Nuclear envelope

Aerobic heterotrophic

prokaryote

Mitochondrion

Plastid

Ancestral

heterotrophic eukaryote

Ancestral photosynthetic

eukaryote


Key evidence supporting an endosymbiotic origin of mitochondria and plastids:

Inner membranes are similar to plasma membranes of prokaryotes

Division is similar in these organelles and some prokaryotes

These organelles transcribe and translate their own DNA

Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

© 2011 Pearson Education, Inc.


The cambrian explosion
The Cambrian Explosion mitochondria and plastids:

The Cambrian explosion refers to the sudden appearance of a multitude of modern body designs (530 million years ago)

first evidence of predator-prey interactions

© 2011 Pearson Education, Inc.


Figure 25 10
Figure 25.10 mitochondria and plastids:

Sponges

Cnidarians

Echinoderms

Chordates

Brachiopods

Annelids

Molluscs

Arthropods

PROTEROZOIC

PALEOZOIC

Ediacaran

Cambrian

635

605

575

545

515

485

0

Time (millions of years ago)


The colonization of land
The Colonization of Land mitochondria and plastids:

Fungi, plants, and animals began to colonize land about 500 million years ago

Vascular tissue in plants transports materials internally and appeared by about 420 million years ago

Plants and fungi today form mutually beneficial associations and likely colonized land together

© 2011 Pearson Education, Inc.


Arthropods and tetrapods are the most widespread and diverse land animals

Tetrapods evolved from lobe-finned fishes around 365 million years ago

© 2011 Pearson Education, Inc.


The history of life on Earth has seen the rise and fall of many groups of organisms

The rise and fall of groups depends on speciation and extinction rates within the group

Concept 25.4: The rise and fall of groups of organisms reflect differences in speciation and extinction rates

© 2011 Pearson Education, Inc.


© 2011 Pearson Education, Inc. many groups of organisms

Video: Volcanic Eruption


© 2011 Pearson Education, Inc. many groups of organisms

Video: Lava Flow


Figure 25 14
Figure 25.14 many groups of organisms

Present

Cenozoic

Eurasia

North America

Africa

65.5

India

South

America

Madagascar

Australia

Antarctica

Laurasia

135

Millions of years ago

Gondwana

Mesozoic

251

Pangaea

Paleozoic


Continental drift has many effects on living organisms many groups of organisms

A continent’s climate can change as it moves north or south

Separation of land masses can lead to allopatric speciation

© 2011 Pearson Education, Inc.


Mass extinctions
Mass Extinctions many groups of organisms

The fossil record shows that most species that have ever lived are now extinct

At times, the rate of extinction has increased dramatically and caused a mass extinction, and is the result of disruptive global environmental changes

© 2011 Pearson Education, Inc.


The big five mass extinction events
The “Big Five” Mass Extinction Events many groups of organisms

In each of the five mass extinction events, more than 50% of Earth’s species became extinct

© 2011 Pearson Education, Inc.


Figure 25 15
Figure 25.15 many groups of organisms

1,100

1,000

25

900

800

20

700

600

15

Total extinction rate

(families per million years):

Number of families:

500

400

10

300

200

5

100

0

0

Mesozoic

Cenozoic

Paleozoic

Era

Q

D

P

E

O

S

C

Tr

J

C

P

N

Period

488

444

145

416

359

299

251

65.5

0

542

200


The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras 251 million years ago

This mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species

© 2011 Pearson Education, Inc.


A number of factors might have contributed to these extinctions

Intense volcanism in what is now Siberia

Global warming resulting from the emission of large amounts of CO2 from the volcanoes

Reduced temperature gradient from equator to poles

Oceanic anoxia from reduced mixing of ocean waters

© 2011 Pearson Education, Inc.


Is a sixth mass extinction under way
Is a Sixth Mass Extinction Under Way? extinctions

Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate

Extinction rates tend to increase when global temperatures increase

Data suggest that a sixth, human-caused mass extinction is likely to occur unless dramatic action is taken

© 2011 Pearson Education, Inc.


Figure 25 17
Figure 25.17 extinctions

Mass extinctions

3

2

1

Relative extinction rate of marine animal genera

0

1

2

0

2

1

1

2

3

4

3

Cooler

Warmer

Relative temperature


Figure 25 16
Figure 25.16 extinctions

NORTH AMERICA

Chicxulub

crater

Yucatán

Peninsula


Consequences of mass extinctions
Consequences of Mass Extinctions extinctions

Mass extinction can pave the way for adaptive radiations

© 2011 Pearson Education, Inc.


Worldwide adaptive radiations
Worldwide Adaptive Radiations extinctions

Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs

Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods

© 2011 Pearson Education, Inc.


Studying genetic mechanisms of change can provide insight into large-scale evolutionary change

Concept 25.5: Major changes in body form can result from changes in the sequences and regulation of developmental genes

© 2011 Pearson Education, Inc.


Changes in rate and timing
Changes in Rate and Timing into large-scale evolutionary change

Heterochrony is an evolutionary change in the rate or timing of developmental events

It can have a significant impact on body shape

The contrasting shapes of human and chimpanzee skulls are the result of small changes in relative growth rates

© 2011 Pearson Education, Inc.


Figure 25 21
Figure 25.21 into large-scale evolutionary change

Chimpanzee infant

Chimpanzee adult

Chimpanzee fetus

Chimpanzee adult

Human fetus

Human adult


Figure 25 22
Figure 25.22 into large-scale evolutionary change

  • In paedomorphosis, the rate of reproductive development accelerates compared with somatic development

  • The sexually mature species may retain body features that were juvenile structures in an ancestral species

Gills


Concept 25 6 evolution is not goal oriented
Concept 25.6: Evolution is not goal oriented into large-scale evolutionary change

Evolution is like tinkering—it is a process in which new forms arise by the slight modification of existing forms

© 2011 Pearson Education, Inc.


Evolutionary novelties
Evolutionary Novelties into large-scale evolutionary change

Most novel biological structures evolve in many stages from previously existing structures

Complex eyes have evolved from simple photosensitive cells independently many times

Exaptations are structures that evolve in one context but become co-opted for a different function

Natural selection can only improve a structure in the context of its current utility

© 2011 Pearson Education, Inc.


Figure 25 26
Figure 25.26 into large-scale evolutionary change

(a) Patch of pigmented cells

(b) Eyecup

Pigmented cells

(photoreceptors)

Pigmented

cells

Epithelium

Nerve fibers

Nerve fibers

(e) Complex camera lens-type eye

(c) Pinhole camera-type eye

(d) Eye with primitive lens

Cornea

Epithelium

Cellular

mass

(lens)

Cornea

Fluid-filled

cavity

Lens

Retina

Optic nerve

Optic

nerve

Optic nerve

Pigmented

layer

(retina)


Figure 25 27
Figure 25.27 into large-scale evolutionary change

Holocene

0

Equus

Pleistocene

Hippidion and

close relatives

Pliocene

5

Nannippus

Pliohippus

Neohipparion

Sinohippus

Callippus

10

Hipparion

Miocene

Megahippus

Hypohippus

Archaeohippus

15

Anchitherium

Parahippus

Merychippus

20

25

Millions of years ago

Miohippus

Oligocene

30

Haplohippus

35

Mesohippus

Palaeotherium

Key

Grazers

Pachynolophus

Epihippus

40

Browsers

Propalaeotherium

Eocene

45

Orohippus

50

Hyracotherium

relatives

55

Hyracotherium


Chapter 26 into large-scale evolutionary change

Phylogeny and the Tree of Life


Figure 26 1
Figure 26.1 into large-scale evolutionary change

What type of animal is this?...why do you say?


© 2011 Pearson Education, Inc. into large-scale evolutionary change

  • Phylogeny is the evolutionary history of a species or group of related species

  • The discipline of systematics classifies organisms and determines their evolutionary relationships

    • Systematists use fossil, molecular, and genetic data to infer evolutionary relationships


Figure 26 2a
Figure 26.2a into large-scale evolutionary change

Create a cladogram of…


Figure 26 2b
Figure 26.2b into large-scale evolutionary change


Figure 26 2c
Figure 26.2c into large-scale evolutionary change


Figure 26 2
Figure 26.2 into large-scale evolutionary change


Create a cladogram of the following
Create a cladogram of the following into large-scale evolutionary change

  • AAG CAT ATA CGT

  • GAG CAT ATA CAT

  • ACG GAT ATA CGT

  • ACG GGT ATA CGC


Calculate the percent similarity
Calculate the percent similarity into large-scale evolutionary change

  • ACG GGT ATA CGC

  • ACG GAT ATA CGT

  • AAG CAT ATA CGT

  • GAG CAT ATA CAT


Concept 26 1 phylogenies show evolutionary relationships

© 2011 Pearson Education, Inc. into large-scale evolutionary change

Concept 26.1: Phylogenies show evolutionary relationships

  • Taxonomy is the ordered division and naming of organisms


Figure 26 3
Figure 26.3 into large-scale evolutionary change

Species:

Panthera pardus

Genus:

Panthera

Family:

Felidae

Order:

Carnivora

Class:

Mammalia

Phylum:

Chordata

Kingdom:

Animalia

Domain:

Bacteria

Domain:

Archaea

Domain:

Eukarya


Linking classification and phylogeny

© 2011 Pearson Education, Inc. into large-scale evolutionary change

Linking Classification and Phylogeny

  • Systematists depict evolutionary relationships in branching phylogenetic trees


Figure 26 4

Order into large-scale evolutionary change

Family

Genus

Species

Figure 26.4

Panthera

pardus

(leopard)

Felidae

Panthera

Taxidea

taxus

(American

badger)

Taxidea

Carnivora

Mustelidae

Lutra lutra

(European

otter)

Lutra

Canis

latrans

(coyote)

Canidae

Canis

Canis

lupus

(gray wolf)


Figure 26 5

Branch point: into large-scale evolutionary change

where lineages diverge

Figure 26.5

Taxon A

Taxon B

Sister

taxa

Taxon C

Taxon D

Taxon E

ANCESTRAL

LINEAGE

Taxon F

Basal

taxon

Taxon G

This branch point forms a

polytomy: an unresolved

pattern of divergence.

This branch point

represents the

common ancestor of

taxa A–G.


© 2011 Pearson Education, Inc. into large-scale evolutionary change

  • A phylogenetic tree represents a hypothesis about evolutionary relationships

  • Each branch point represents the divergence of two species

  • Sister taxa are groups that share an immediate common ancestor


© 2011 Pearson Education, Inc. into large-scale evolutionary change

  • A rooted tree includes a branch to represent the last common ancestor of all taxa in the tree

  • A basal taxon diverges early in the history of a group and originates near the common ancestor of the group

  • A polytomy is a branch from which more than two groups emerge


Applying phylogenies

© 2011 Pearson Education, Inc. into large-scale evolutionary change

Applying Phylogenies

  • Phylogeny provides important information about similar characteristics in closely related species

  • A phylogeny was used to identify the species of whale from which “whale meat” originated


Figure 26 6

RESULTS into large-scale evolutionary change

Minke (Southern Hemisphere)

Figure 26.6

Unknowns #1a, 2, 3, 4, 5, 6, 7, 8

Minke (North Atlantic)

Unknown #9

Humpback (North Atlantic)

Humpback (North Pacific)

Unknown #1b

Gray

Blue

Unknowns #10, 11, 12

Unknown #13

Fin (Mediterranean)

Fin (Iceland)


Concept 26 2 phylogenies are inferred from morphological and molecular data

© 2011 Pearson Education, Inc. into large-scale evolutionary change

Concept 26.2: Phylogenies are inferred from morphological and molecular data

  • To infer phylogenies, systematists gather information about morphologies, genes, and biochemistry of living organisms


Sorting homology from analogy

© 2011 Pearson Education, Inc. into large-scale evolutionary change

Sorting Homology from Analogy

  • When constructing a phylogeny, systematists need to distinguish whether a similarity is the result of homology or analogy

    • Homology is similarity due to shared ancestry

      • The more complex two similar structures are, the more likely it is that they are homologous

    • Analogy is similarity due to convergent evolution



Evaluating molecular homologies

© 2011 Pearson Education, Inc. characteristics.

Evaluating Molecular Homologies

  • Systematists use computer programs and mathematical tools when analyzing comparable DNA segments from different organisms


Figure 26 8 4
Figure 26.8-4 characteristics.

1

1

2

Deletion

2

1

2

Insertion

3

1

2

4

1

2


Concept 26 3 shared characters are used to construct phylogenetic trees

© 2011 Pearson Education, Inc. characteristics.

Concept 26.3: Shared characters are used to construct phylogenetic trees

  • Once homologous characters have been identified, they can be used to infer a phylogeny


Cladistics

© 2011 Pearson Education, Inc. characteristics.

Cladistics

  • Cladistics groups organisms by common descent

  • A clade is a group of species that includes an ancestral species and all its descendants

    • Clades can be nested in larger clades, but not all groupings of organisms qualify as clades


Figure 26 10
Figure 26.10 characteristics.

(b) Paraphyletic group

(c) Polyphyletic group

(a) Monophyletic group (clade)

A

A

A

B

B

B

Group 

Group 

C

C

C

D

D

D

E

E

Group 

E

F

F

F

G

G

G

  • A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants


© 2011 Pearson Education, Inc. characteristics.

  • A shared ancestral character is a character that originated in an ancestor of the taxon

  • A shared derived character is an evolutionary novelty unique to a particular clade

  • What are some examples?


Figure 26 11
Figure 26.11 characteristics.

Lancelet

(outgroup)

TAXA

Lancelet

(outgroup)

Lamprey

Lamprey

Leopard

Turtle

Bass

Frog

Vertebral

column

(backbone)

Bass

0

1

1

1

1

1

Vertebral

column

Hinged jaws

0

0

1

1

1

1

Frog

Hinged jaws

Four walking

legs

0

0

0

1

1

CHARACTERS

1

Turtle

Four walking legs

0

0

0

0

1

1

Amnion

Amnion

Leopard

Hair

0

0

0

0

1

0

Hair

(b) Phylogenetic tree

(a) Character table


© 2011 Pearson Education, Inc. characteristics.

  • An outgroup is a species or group of species that is closely related to the ingroup, the various species being studied

    • The outgroup is a group that has diverged before the ingroup

    • Systematists compare each ingroup species with the outgroup to differentiate between shared derived and shared ancestral characteristics


Figure 26 12
Figure 26.12 characteristics.

Drosophila

Lancelet

Zebrafish

Frog

Chicken

Human

Mouse

  • In some trees, the length of a branch can reflect the number of genetic changes that have taken place in a particular DNA sequence in that lineage


Drosophila

Lancelet

Zebrafish

Frog

Chicken

Human

Mouse

MESOZOIC

CENOZOIC

PALEOZOIC

251

65.5

Present

542

Millions of years ago


© 2011 Pearson Education, Inc. characteristics.

Systematists can never be sure of finding

the best tree in a large data set

  • Maximum parsimony assumes that the tree that requires the fewest evolutionary events (appearances of shared derived characters) is the most likely

  • The principle of maximum likelihood states that, given certain rules about how DNA changes over time, a tree can be found that reflects the most likely sequence of evolutionary events


Figure 26 14

Human characteristics.

Tulip

Mushroom

Figure 26.14

40%

30%

0

Human

40%

Mushroom

0

Tulip

0

(a) Percentage differences between sequences

5%

15%

5%

15%

15%

10%

25%

20%

Tree 1: More likely

Tree 2: Less likely

(b) Comparison of possible trees


Figure 26 15

TECHNIQUE characteristics.

Figure 26.15

Species 

Species 

Species 

1

Three phylogenetic hypotheses:













Site

2

1

2

3

4

Species 

C

T

A

T

Species 

C

T

T

C

Species 

A

G

A

C

Ancestral sequence

A

G

T

T

3

1/C



1/C







1/C





1/C

1/C

4

3/A

3/A

2/T



2/T

3/A

4/C







4/C

4/C

2/T





2/T

2/T

3/A

4/C

3/A

4/C

RESULTS













7 events

6 events

7 events


Phylogenetic trees as hypotheses

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Phylogenetic Trees as Hypotheses

  • The best hypotheses for phylogenetic trees fit the most data: morphological, molecular, and fossil

  • Phylogenetic bracketingallows us to predict features of an ancestor from features of its descendants

    • For example, phylogenetic bracketing allows us to infer characteristics of dinosaurs


Figure 26 16
Figure 26.16 characteristics.

Lizards

and snakes

Crocodilians

Ornithischian

dinosaurs

Common

ancestor of

crocodilians,

dinosaurs,

and birds

Saurischian

dinosaurs

Birds


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  • Birds and crocodiles share several features: four-chambered hearts, song, nest building, and brooding

  • These characteristics likely evolved in a common ancestor and were shared by all of its descendants, including dinosaurs

  • The fossil record supports nest building and brooding in dinosaurs


Figure 26 17
Figure 26.17 characteristics.

Front limb

Hind limb

Eggs

(a) Fossil remains of

Oviraptor and eggs

(b) Artist’s reconstruction of the dinosaur’s

posture based on the fossil findings


Concept 26 4 an organism s evolutionary history is documented in its genome

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Concept 26.4: An organism’s evolutionary history is documented in its genome

  • Comparing nucleic acids or other molecules to infer relatedness is a valuable approach for tracing organisms’ evolutionary history

  • DNA that codes for rRNA changes relatively slowly and is useful for investigating branching points hundreds of millions of years ago

  • mtDNA evolves rapidly and can be used to explore recent evolutionary events


Figure 26 18
Figure 26.18 characteristics.

Formation of orthologous genes:

a product of speciation

Formation of paralogous genes:

within a species

Ancestral gene

Ancestral gene

Species C

Ancestral species

Speciation with

divergence of gene

Gene duplication and divergence

Orthologous genes

Paralogous genes

Species B

Species A

Species C after many generations


Genome evolution

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Genome Evolution

  • Orthologous genes are widespread and extend across many widely varied species

    • For example, humans and mice diverged about 65 million years ago, and 99% of our genes are orthologous


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  • Gene number and the complexity of an organism are not strongly linked

    • For example, humans have only four times as many genes as yeast, a single-celled eukaryote

  • Genes in complex organisms appear to be very versatile, and each gene can perform many functions


Concept 26 5 molecular clocks help track evolutionary time

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Concept 26.5: Molecular clocks help track evolutionary time

  • To extend molecular phylogenies beyond the fossil record, we must make an assumption about how change occurs over time


Molecular clocks

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Molecular Clocks

  • A molecular clock uses constant rates of evolution in some genes to estimate the absolute time of evolutionary change

  • In orthologous genes, nucleotide substitutions are proportional to the time since they last shared a common ancestor

  • In paralogous genes, nucleotide substitutions are proportional to the time since the genes became duplicated


Figure 26 19
Figure 26.19 characteristics.

90

60

Number of mutations

30

0

60

120

90

30

Divergence time (millions of years)


Neutral theory

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Neutral Theory

  • Neutral theory states that much evolutionary change in genes and proteins has no effect on fitness and is not influenced by natural selection

  • It states that the rate of molecular change in these genes and proteins should be regular like a clock


Problems with molecular clocks

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Problems with Molecular Clocks

  • The molecular clock does not run as smoothly as neutral theory predicts

  • Irregularities result from natural selection in which some DNA changes are favored over others

  • Estimates of evolutionary divergences older than the fossil record have a high degree of uncertainty

  • The use of multiple genes may improve estimates


Applying a molecular clock the origin of hiv

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Applying a Molecular Clock: The Origin of HIV

  • Phylogenetic analysis shows that HIV is descended from viruses that infect chimpanzees and other primates

  • HIV spread to humans more than once

  • Comparison of HIV samples shows that the virus evolved in a very clocklike way

  • Application of a molecular clock to one strain of HIV suggests that that strain spread to humans during the 1930s


Figure 26 20

0.20 characteristics.

Figure 26.20

0.15

HIV

Index of base changes between HIV gene sequences

0.10

Range

Adjusted best-fit line

(accounts for uncertain

dates of HIV sequences)

0.05

0

1900

1920

1940

1960

1980

2000

Year


Concept 26 6 new information continues to revise our understanding of the tree of life

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Concept 26.6: New information continues to revise our understanding of the tree of life

  • Recently, we have gained insight into the very deepest branches of the tree of life through molecular systematics


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Animation: Classification SchemesRight-click slide / select “Play”


Figure 26 21

Eukarya characteristics.

Figure 26.21

Land plants

Dinoflagellates

Forams

Green algae

Diatoms

Ciliates

Red algae

Amoebas

Cellular slime molds

Euglena

Trypanosomes

Animals

Leishmania

Fungi

Green

nonsulfur bacteria

Sulfolobus

Thermophiles

(Mitochondrion)

Spirochetes

Chlamydia

Halophiles

COMMON

ANCESTOR

OF ALL

LIFE

Green

sulfur bacteria

Bacteria

Methanobacterium

Cyanobacteria

Archaea

(Plastids, including

chloroplasts)


© 2011 Pearson Education, Inc. characteristics.

  • There have been substantial interchanges of genes between organisms in different domains

  • Horizontal gene transfer complicates efforts to build a tree of life

    • Horizontal genetransfer is the movement of genes from one genome to another

      • It occurs by exchange of transposable elements and plasmids, viral infection, and fusion of organisms


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Is the Tree of Life Really a Ring?

  • Some researchers suggest that eukaryotes arose as a fusion between a bacterium and archaean

  • If so, early evolutionary relationships might be better depicted by a ring of life instead of a tree of life


Figure 26 23
Figure 26.23 characteristics.

Archaea

Eukarya

Bacteria


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