the history of life on earth - houston community …...made the origin of life possible earth...

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LECTURE PRESENTATIONS

For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson

© 2011 Pearson Education, Inc.

Lectures by

Erin Barley

Kathleen Fitzpatrick

The History of Life on Earth

Chapter 25 Overview: Lost Worlds

• Past organisms were very different from those

now alive

• The fossil record shows macroevolutionary

changes over large time scales, for example:

– The emergence of terrestrial vertebrates

– The impact of mass extinctions

– The origin of flight in birds


Figure 25.1 Figure 25.UN01

Cryolophosaurus skull

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


Synthesis of Organic Compounds on Early

Earth

• 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)


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• In the 1920s, A. I. Oparin and J. B. S. Haldane

hypothesized that the early atmosphere was a

reducing environment

• In 1953, Stanley Miller and Harold Urey conducted

lab experiments that showed that the abiotic

synthesis of organic molecules in a reducing

atmosphere is possible


• However, the evidence is not yet convincing that the early atmosphere was in fact reducing

• Instead of forming in the atmosphere, the first organic compounds may have been synthesized near volcanoes or deep-sea vents

• Miller-Urey type experiments demonstrate that organic molecules could have formed with various possible atmospheres


Video: Hydrothermal Vent

Video: Tubeworms

Figure 25.2

Ma

ss

of

am

ino

ac

ids

(m

g)

Nu

mb

er

of

am

ino

ac

ids

20

10

0

1953 2008

200

100

0

1953 2008

Figure 25.2a

Mass o

f am

ino

acid

s (

mg

)

Nu

mb

er

of

am

ino

acid

s

20

10

0

1953 2008

200

100

0

1953 2008

Figure 25.2b

• Amino acids have also been found in meteorites


25_02HydrothermalVent_SV.mpg

25_02Tubeworms_SV.mpg

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Abiotic Synthesis of Macromolecules

• RNA monomers have been produced

spontaneously from simple molecules

• Small organic molecules polymerize when they

are concentrated on hot sand, clay, or rock


Protocells

• Replication and metabolism are key properties of

life and may have appeared together

• Protocells may have been fluid-filled vesicles with

a membrane-like structure

• 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


Figure 25.3

(a) Self-assembly

Time (minutes)

Precursor molecules plus

montmorillonite clay

Precursor

molecules only

Re

lati

ve

tu

rbid

ity,

an

in

de

x o

f v

es

icle

nu

mb

er

0

20 m

(b) Reproduction (c) Absorption of RNA

Vesicle boundary

1 m

0

0.2

0.4

40 20 60

Figure 25.3a

Time (minutes)

Precursor molecules plus

montmorillonite clay

Precursor

molecules only

Rela

tive t

urb

idit

y,

an

in

dex o

f vesic

le n

um

ber

0 20 40 60 0

0.2

0.4

(a) Self-assembly

Figure 25.3b

20 m

(b) Reproduction

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Figure 25.3c

(c) Absorption of RNA

Vesicle boundary

1 m

Self-Replicating RNA 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

– For example, ribozymes can make

complementary copies of short stretches of RNA


• Natural selection has produced self-replicating

RNA molecules

• RNA molecules that were more stable or

replicated more quickly would have left the most

descendent RNA molecules

• The early genetic material might have formed an

“RNA world”


• Vesicles with RNA capable of replication would

have been protocells

• RNA could have provided the template for DNA, a

more stable genetic material


Concept 25.2: The fossil record documents

the history of life

• The fossil record reveals changes in the history of

life on Earth


The Fossil Record

• Sedimentary rocks are deposited into layers

called strata and are the richest source of fossils


Video: Grand Canyon

25_04GrandCanyon_SV.mpg

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Dimetrodon

Stromatolites

Fossilized stromatolite

Coccosteus cuspidatus

4.5 cm

0.5 m

2.5

cm

Present

Rhomaleosaurus victor

Tiktaalik

Hallucigenia

Dickinsonia costata

Tappania

1 cm

1 m

100 mya

175

200

300

375 400

500 525

565

600

1,500

3,500

270

Figure 25.4 Figure 25.4a

Fossilized stromatolite

Figure 25.4b

Stromatolites

Figure 25.4c

Tappania

Figure 25.4d

2.5

cm

Dickinsonia

costata

Figure 25.4e

Hallucigenia

1 cm

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Figure 25.4f

4.5 cm

Coccosteus cuspidatus

Figure 25.4g

Tiktaalik

Figure 25.4h

Dimetrodon

0.5 m

Figure 25.4i

Rhomaleosaurus

victor

1 m

• 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


Animation: The Geologic Record

• Fossil discoveries can be a matter of chance or

prediction

– For example, paleontologists found Tiktaalik, an

early terrestrial vertebrate, by targeting

sedimentary rock from a specific time and

environment


25_15GeologicRecord_A.html

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How Rocks and Fossils Are Dated

• 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


Accumulating

“daughter”

isotope

Fra

cti

on

of

pa

ren

t

iso

top

e r

em

ain

ing

Remaining

“parent” isotope

Time (half-lives)

1 2 3 4

1 2

1 4

1 8

1 16

Figure 25.5

• 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


The Origin of New Groups of Organisms

• Mammals belong to the group of animals called

tetrapods

• The evolution of unique mammalian features can

be traced through gradual changes over time


OTHER

TETRA-

PODS

Temporal

fenestra

Hinge

†Dimetrodon

†Very late (non-

mammalian)

cynodonts

Mammals

Sy

na

ps

ids

Th

era

ps

ids

Cy

no

do

nts

Reptiles

(including

dinosaurs and birds)

Key to skull bones

Articular

Quadrate Squamosal

Dentary

Temporal

fenestra

Hinge Hinge

Hinge

Hinges

Temporal

fenestra

(partial view)

Early cynodont (260 mya)

Very late cynodont (195 mya)

Synapsid (300 mya)

Therapsid (280 mya)

Later cynodont (220 mya)

Figure 25.6 Figure 25.6a

OTHER

TETRAPODS †Dimetrodon

†Very late (non-

mammalian)

cynodonts

Mammals

Syn

ap

sid

s

Th

era

psid

s

Cyn

od

on

ts

Reptiles

(including

dinosaurs and birds)

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Figure 25.6b

Temporal

fenestra

Hinge

Temporal

fenestra

Hinge

Synapsid (300 mya)

Therapsid (280 mya)

Key to skull bones

Articular

Quadrate

Squamosal

Dentary

Figure 25.6c

Hinge

Hinge

Hinges

Temporal

fenestra

(partial view)

Early cynodont (260 mya)

Very late cynodont (195 mya)

Later cynodont (220 mya)

Key to skull bones

Articular

Quadrate

Squamosal

Dentary

• The geologic 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


Table 25.1

Table 25.1a Table 25.1b

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• Major boundaries between geological divisions

correspond to extinction events in the fossil record


Origin of solar

system and

Earth

Prokaryotes

Atmospheric oxygen

Archaean

4

3

Figure 25.7-1

Origin of solar

system and

Earth

Prokaryotes

Atmospheric oxygen

Archaean

4

3

Proterozoic

2

Animals

Multicellular

eukaryotes

Single-celled

eukaryotes

1

Figure 25.7-2

Origin of solar

system and

Earth

Prokaryotes

Atmospheric oxygen

Archaean

4

3

Proterozoic

2

Animals

Multicellular

eukaryotes

Single-celled

eukaryotes

Colonization

of land

Humans

Cenozoic

1

Figure 25.7-3

Prokaryotes

1

2 3

4

Figure 25.UN02

The First Single-Celled Organisms

• The oldest known fossils are stromatolites, rocks

formed by the accumulation of sedimentary layers

on bacterial mats

• Stromatolites date back 3.5 billion years ago

• Prokaryotes were Earth’s sole inhabitants from 3.5

to about 2.1 billion years ago


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Figure 25.UN03

Atmospheric oxygen

1

2 3

4

Photosynthesis and the Oxygen Revolution

• Most atmospheric oxygen (O2) is of biological

origin

• O2 produced by oxygenic photosynthesis reacted

with dissolved iron and precipitated out to form

banded iron formations


• By about 2.7 billion years ago, O2 began

accumulating in the atmosphere and rusting iron-

rich terrestrial rocks

• This “oxygen revolution” from 2.7 to 2.3 billion

years ago caused the extinction of many

prokaryotic groups

• Some groups survived and adapted using cellular

respiration to harvest energy


Figure 25.8

“Oxygen

revolution”

Time (billions of years ago)

4 3 2 1 0

1,000

100

10

1

0.1

0.01

0.0001

Atm

osp

he

ric O

2

(perc

en

t o

f p

resen

t-d

ay l

evels

; lo

g s

cale

)

0.001

• The early rise in O2 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


Figure 25.UN04

Single-

celled

eukaryotes

1

2 3

4

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The First Eukaryotes

• The oldest fossils of eukaryotic cells date back 2.1 billion years

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

• 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


• The prokaryotic ancestors of mitochondria and

plastids probably gained entry to the host cell as

undigested prey or internal parasites

• In the process of becoming more interdependent,

the host and endosymbionts would have become

a single organism

• Serial endosymbiosis supposes that

mitochondria evolved before plastids through a

sequence of endosymbiotic events


Figure 25.9-1

Plasma membrane

DNA

Cytoplasm

Ancestral

prokaryote

Nuclear envelope

Nucleus Endoplasmic

reticulum

Figure 25.9-2

Plasma membrane

DNA

Cytoplasm

Ancestral

prokaryote

Nuclear envelope

Nucleus Endoplasmic

reticulum

Aerobic heterotrophic

prokaryote

Mitochondrion

Ancestral

heterotrophic eukaryote

Figure 25.9-3

Plasma membrane

DNA

Cytoplasm

Ancestral

prokaryote

Nuclear envelope

Nucleus Endoplasmic

reticulum

Aerobic heterotrophic

prokaryote

Mitochondrion

Ancestral

heterotrophic eukaryote

Photosynthetic

prokaryote

Mitochondrion

Plastid

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


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The Origin of Multicellularity

• The evolution of eukaryotic cells allowed for a

greater range of unicellular forms

• A second wave of diversification occurred when

multicellularity evolved and gave rise to algae,

plants, fungi, and animals


Figure 25.UN05

Multicellular

eukaryotes

1

2 3

4

The Earliest Multicellular Eukaryotes

• Comparisons of DNA sequences date the

common ancestor of multicellular eukaryotes to

1.5 billion years ago

• The oldest known fossils of multicellular

eukaryotes are of small algae that lived about 1.2

billion years ago


• The “snowball Earth” hypothesis suggests that

periods of extreme glaciation confined life to the

equatorial region or deep-sea vents from 750 to

580 million years ago

• The Ediacaran biota were an assemblage of larger

and more diverse soft-bodied organisms that lived

from 575 to 535 million years ago


Figure 25.UN06

Animals

1

2 3

4

The Cambrian Explosion

• The Cambrian explosion refers to the sudden appearance of fossils resembling modern animal phyla in the Cambrian period (535 to 525 million years ago)

• A few animal phyla appear even earlier: sponges, cnidarians, and molluscs

• The Cambrian explosion provides the first evidence of predator-prey interactions


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Figure 25.10

Sponges

Cnidarians

Echinoderms

Chordates

Brachiopods

Annelids

Molluscs

Arthropods

Ediacaran Cambrian

PROTEROZOIC PALEOZOIC

Time (millions of years ago)

635 605 575 545 515 485 0

• DNA analyses suggest that many animal phyla

diverged before the Cambrian explosion, perhaps

as early as 700 million to 1 billion years ago

• Fossils in China provide evidence of modern

animal phyla tens of millions of years before the

Cambrian explosion

• The Chinese fossils suggest that “the Cambrian

explosion had a long fuse”


Figure 25.11

150 m (b) Later stage 200 m (a) Two-cell stage

Figure 25.11a

150 m (a) Two-cell stage

Figure 25.11b

(b) Later stage 200 m

Figure 25.UN07

Colonization of land

1

2 3

4

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The Colonization of Land

• 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


• Arthropods and tetrapods are the most

widespread and diverse land animals

• Tetrapods evolved from lobe-finned fishes around

365 million years ago


• 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


Video: Lava Flow

Video: Volcanic Eruption

Plate Tectonics

• At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago

• According to the theory of plate tectonics, Earth’s crust is composed of plates floating on Earth’s mantle


Figure 25.12

Crust

Mantle

Outer

core

Inner

core

• Tectonic plates move slowly through the process of continental drift

• Oceanic and continental plates can collide, separate, or slide past each other

• Interactions between plates cause the formation of mountains and islands, and earthquakes


25_13bLavaFlow_SV.mpg

25_13bVolcanicEruption_SV.mpg

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Figure 25.13

Juan de Fuca

Plate

North

American

Plate

Caribbean

Plate

Cocos Plate

Pacific

Plate Nazca

Plate

South

American

Plate

Eurasian Plate

Philippine

Plate

Indian

Plate

African

Plate

Antarctic

Plate

Australian

Plate

Scotia Plate

Arabian

Plate

Consequences of Continental Drift

• Formation of the supercontinent Pangaea about

250 million years ago had many effects

– A deepening of ocean basins

– A reduction in shallow water habitat

– A colder and drier climate inland


Figure 25.14

65.5

135

251

Pre

se

nt

Ce

no

zo

ic

Eurasia

Africa

South America

India

Antarctica

Madagascar

Me

so

zo

ic

Pa

leo

zo

ic

Millio

ns

of

ye

ars

ag

o

Laurasia

Figure 25.14a

135

251

Meso

zo

ic

Pale

ozo

ic

Millio

ns o

f years

ag

o

Laurasia

Figure 25.14b

65.5

Pre

sen

t

Cen

ozo

ic

Eurasia

Africa

South

America

India

Antarctica

Madagascar

Millio

ns o

f years

ag

o

• Continental drift has many effects on living

organisms

– A continent’s climate can change as it moves

north or south

– Separation of land masses can lead to allopatric

speciation


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• The distribution of fossils and living groups reflects

the historic movement of continents

– For example, the similarity of fossils in parts of

South America and Africa is consistent with the

idea that these continents were formerly attached


Mass Extinctions

• The fossil record shows that most species that

have ever lived are now extinct

• Extinction can be caused by changes to a species’

environment

• At times, the rate of extinction has increased

dramatically and caused a mass extinction

• Mass extinction is the result of disruptive global

environmental changes


The “Big Five” Mass Extinction Events

• In each of the five mass extinction events, more

than 50% of Earth’s species became extinct


25

20

15

10

5

0

542 488 444

Era

Period

416

E O S D

359 299

C

251

P Tr

200 65.5

J C

Mesozoic

P N

Cenozoic

0

0

Q

100

200

300

400

500

600

700

800

900

1,000

1,100

To

tal e

xti

nc

tio

n r

ate

(fa

milie

s p

er

millio

n y

ea

rs):

Nu

mb

er

of

fam

ilie

s:

Paleozoic

145

Figure 25.15

• 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


• A number of factor 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


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• The Cretaceous mass extinction 65.5 million years

ago separates the Mesozoic from the Cenozoic

• Organisms that went extinct include about half of

all marine species and many terrestrial plants and

animals, including most dinosaurs


• The presence of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago

• Dust clouds caused by the impact would have blocked sunlight and disturbed global climate

• The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time


Figure 25.16

NORTH

AMERICA

Yucatán

Peninsula

Chicxulub

crater

Is a Sixth Mass Extinction Under Way?

• 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


Mass extinctions

Cooler Warmer

Rela

tive e

xti

ncti

on

rate

of

mari

ne a

nim

al g

en

era

3

2

1

0

1

2 3 2 1 0 1 2 3 4

Relative temperature

Figure 25.17

Consequences of Mass Extinctions

• Mass extinction can alter ecological communities and the niches available to organisms

• It can take from 5 to 100 million years for diversity to recover following a mass extinction

• The percentage of marine organisms that were predators increased after the Permian and Cretaceous mass extinctions

• Mass extinction can pave the way for adaptive radiations


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Figure 25.18

Pre

da

tor

ge

ne

ra

(pe

rce

nta

ge

of

ma

rin

e g

en

era

) 50

40

30

20

10

0 Era

Period

542 488 444 416

E O S D

359 299

C

251

P Tr

200 65.5

J C

Mesozoic

P N

Cenozoic

0

Paleozoic

145 Q

Cretaceous mass

extinction

Permian mass

extinction


Adaptive Radiations

• Adaptive radiation is the evolution of diversely adapted species from a common ancestor

• Adaptive radiations may follow

– Mass extinctions

– The evolution of novel characteristics

– The colonization of new regions


Worldwide Adaptive Radiations

• Mammals underwent an adaptive radiation after

the extinction of terrestrial dinosaurs

• The disappearance of dinosaurs (except birds)

allowed for the expansion of mammals in diversity

and size

• Other notable radiations include photosynthetic

prokaryotes, large predators in the Cambrian, land

plants, insects, and tetrapods


Figure 25.19

Ancestral

mammal

ANCESTRAL

CYNODONT

250 200 150 100 50 0


Monotremes

(5 species)

Marsupials

(324 species)

Eutherians

(5,010

species)

Regional Adaptive Radiations

• Adaptive radiations can occur when organisms

colonize new environments with little competition

• The Hawaiian Islands are one of the world’s great

showcases of adaptive radiation


Close North American relative,

the tarweed Carlquistia muirii

KAUAI 5.1

million years OAHU

3.7 million years

1.3 million years

MOLOKAI

LANAI MAUI

HAWAII

0.4 million years

N

Argyroxiphium

sandwicense

Dubautia laxa

Dubautia scabra

Dubautia linearis

Dubautia waialealae

Figure 25.20

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Figure 25.20a

KAUAI

OAHU 1.3

million years

MOLOKAI

LANAI MAUI

HAWAII 0.4

million years

N

5.1 million years

3.7 million years

Figure 25.20b

Close North American relative,

the tarweed Carlquistia muirii

Figure 25.20c

Argyroxiphium sandwicense

Figure 25.20d

Dubautia linearis

Figure 25.20e

Dubautia scabra

Figure 25.20f

Dubautia waialealae

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Figure 25.20g

Dubautia laxa

• 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


Effects of Development Genes

• Genes that program development control the rate,

timing, and spatial pattern of changes in an

organism’s form as it develops into an adult


Changes in Rate and Timing

• 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


Animation: Allometric Growth

Figure 25.21

Chimpanzee infant Chimpanzee adult

Chimpanzee adult

Human adult Human fetus

Chimpanzee fetus

Figure 25.21a

Chimpanzee infant Chimpanzee adult

25_21AllometricGrowth_A.html

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Figure 25.21b

Chimpanzee adult

Human adult Human fetus

Chimpanzee fetus

• Heterochrony can alter the timing of reproductive

development relative to the development of

nonreproductive organs

• 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


Figure 25.22

Gills

Changes in Spatial Pattern

• Substantial evolutionary change can also result

from alterations in genes that control the

placement and organization of body parts

• Homeotic genes determine such basic features

as where wings and legs will develop on a bird or

how a flower’s parts are arranged


• Hox genes are a class of homeotic genes that

provide positional information during development

• If Hox genes are expressed in the wrong location,

body parts can be produced in the wrong location

• For example, in crustaceans, a swimming

appendage can be produced instead of a feeding

appendage


Figure 25.23

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Figure 25.23a Figure 25.23b

The Evolution of Development

• The tremendous increase in diversity during the

Cambrian explosion is a puzzle

• Developmental genes may play an especially

important role

• Changes in developmental genes can result in

new morphological forms


Changes in Genes

• New morphological forms likely come from gene

duplication events that produce new

developmental genes

• A possible mechanism for the evolution of six-

legged insects from a many-legged crustacean

ancestor has been demonstrated in lab

experiments

• Specific changes in the Ubx gene have been

identified that can “turn off” leg development


Figure 25.24

Hox gene 6 Hox gene 7 Hox gene 8

Ubx

About 400 mya

Drosophila Artemia

Changes in Gene Regulation

• Changes in morphology likely result from changes

in the regulation of developmental genes rather

than changes in the sequence of developmental

genes

– For example, threespine sticklebacks in lakes

have fewer spines than their marine relatives

– The gene sequence remains the same, but the

regulation of gene expression is different in the

two groups of fish


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Figure 25.25a

Threespine stickleback

(Gasterosteus aculeatus)

Ventral spines

Figure 25.25b

Test of Hypothesis A:

Differences in the coding

sequence of the Pitx1 gene?

Marine stickleback embryo

Close-up

of mouth

Close-up of ventral surface

Lake stickleback embryo

Test of Hypothesis B:

Differences in the regulation

of expression of Pitx1?

Result:

No

Result:

Yes

The 283 amino acids of the Pitx1 protein

are identical.

Pitx1 is expressed in the ventral spine

and mouth regions of developing marine

sticklebacks but only in the mouth

region of developing lake sticklebacks.

RESULTS

Figure 25.25c

Marine stickleback embryo

Close-up

of mouth

Close-up of ventral surface

Figure 25.25d

Lake stickleback embryo

Concept 25.6: Evolution is not goal oriented

• Evolution is like tinkering—it is a process in which

new forms arise by the slight modification of

existing forms


Evolutionary Novelties

• 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


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24

Figure 25.26

(a) Patch of pigmented cells (b) Eyecup

Pigmented cells

(photoreceptors) Pigmented

cells

Nerve fibers Nerve fibers

Epithelium

Cornea Cornea

Lens

Retina

Optic nerve Optic nerve Optic

nerve

(c) Pinhole camera-type eye (d) Eye with primitive lens (e) Complex camera lens-type eye

Epithelium Fluid-filled

cavity

Cellular

mass

(lens)

Pigmented

layer

(retina)

Figure 25.26a

(a) Patch of pigmented cells

Pigmented cells

(photoreceptors)

Nerve fibers

Epithelium

Figure 25.26b

(b) Eyecup

Pigmented

cells

Nerve fibers

Figure 25.26c

Optic

nerve

(c) Pinhole camera-type eye

Epithelium Fluid-filled

cavity

Pigmented

layer

(retina)

Figure 25.26d

Cornea

Optic nerve

(d) Eye with primitive lens

Cellular

mass

(lens)

Figure 25.26e

Cornea

Lens

Retina

Optic nerve

(e) Complex camera lens-type eye

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25

Evolutionary Trends

• Extracting a single evolutionary progression from

the fossil record can be misleading

• Apparent trends should be examined in a broader

context

• The species selection model suggests that

differential speciation success may determine

evolutionary trends

• Evolutionary trends do not imply an intrinsic drive

toward a particular phenotype


Figure 25.27

Holocene

Pleistocene

Pliocene

0

5

10

Anchitherium

Mio

cen

e

15

20

25

30

Olig

ocen

e

Mill

ion

s o

f years

ag

o

35

40

50

45

55

Eo

cen

e

Equus

Pliohippus

Merychippus

Sin

oh

ipp

us

Meg

ah

ipp

us

Hyp

oh

ipp

us

Arc

haeo

hip

pu

s

Para

hip

pu

s

Mio

hip

pu

s

Mesohippus

Pro

pala

eo

theri

um

Pach

yn

olo

ph

us

Pala

eo

theri

um

Hap

loh

ipp

us

Ep

ihip

pu

s

Oro

hip

pu

s

Hyracotherium relatives

Hyracotherium

Key

Grazers

Browsers

Hip

pari

on

Neo

hip

pari

on

Nan

nip

pu

s

Callip

pu

s H

ipp

idio

n a

nd

clo

se r

ela

tiv

es

Figure 25.27a

25

30

Olig

ocen

e

Mil

lio

ns o

f ye

ars

ag

o

35

40

50

45

55

Eo

cen

e

Mio

hip

pu

s

Mesohippus

Pro

pala

eo

theri

um

Pach

yn

olo

ph

us

Pala

eo

theri

um

Hap

loh

ipp

us

Ep

ihip

pu

s

Oro

hip

pu

s

Hyracotherium

Key

Grazers

Browsers

Hyracotherium relatives

Figure 25.27b

Holocene

Pleistocene

Pliocene

0

5

10

Anchitherium

Mio

cen

e 15

15

20

Equus

Pliohippus

Merychippus

Sin

oh

ipp

us

Meg

ah

ipp

us

Hyp

oh

ipp

us

Arc

haeo

hip

pu

s

Para

hip

pu

s

Hip

pari

on

Neo

hip

pari

on

Nan

nip

pu

s

Callip

pu

s Hip

pid

ion

an

d

clo

se r

ela

tiv

es

Mio

hip

pu

s

Key

Grazers

Browsers

Figure 25.UN08

1.2 bya: First multicellular eukaryotes

4,000 3,500 3,000 2,500 2,000 1,500 1,000 500

Millions of years ago (mya)

3.5 billion years ago (bya): First prokaryotes (single-celled)

2.1 bya: First eukaryotes (single-celled)

500 mya: Colonization of land by fungi, plants, and animals

535525 mya: Cambrian explosion

(great increase in diversity of animal forms)

Pre

sen

t

Figure 25.UN09

1

2 3

4

Proterozoic Archaean

Origin of solar system

and Earth

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26

Figure 25.UN10

Flies and

fleas

Caddisflies

Moths and

butterflies Herbivory

Figure 25.UN11

the history of life on earth - houston community …...made the origin of life possible earth...

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