Millions of years ago

Document technical information

Format pptx
Size 13.8 MB
First found May 22, 2018

Document content analysis

Category Also themed
Language
English
Type
not defined
Concepts
no text concepts found

Persons

Barbara Cook
Barbara Cook

wikipedia, lookup

Organizations

Places

Transcript

Chapter 25
The History of Life on
Earth
Overview: Lost Worlds
• Past organisms were very different from those
now alive.
• The fossil record shows macroevolutionary
changes over large time scales including.
– The emergence of terrestrial vertebrates.
– The origin of photosynthesis.
– Long-term impacts of mass extinctions.
Fig. 25-1
Figure 25.1 What does fossil evidence say about where these dinosaurs lived?
Fig 25-UN1
Cryolophosaurus
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 “protobionts.”
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.
• Earth’s early atmosphere likely contained water
vapor and chemicals released by volcanic
eruptions (nitrogen, nitrogen oxides, carbon
dioxide, methane, ammonia, hydrogen,
hydrogen sulfide).
• A. I. Oparin and J. B. S. Haldane hypothesized
that the early atmosphere was a reducing
environment.
• 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 submerged volcanoes and
deep-sea vents.
Video: Tubeworms
Video: Hydrothermal Vent
Figure
25.2 A
window
to early
life?
• Amino acids have also been found
in meteorites.
Abiotic Synthesis of Macromolecules
• Small organic molecules polymerize when they
are concentrated on hot sand, clay, or rock.
Protobionts
• Replication and metabolism are key properties
of life.
• Protobionts are aggregates of abiotically
produced molecules surrounded by a
membrane or membrane-like structure.
• Protobionts exhibit simple reproduction and
metabolism and maintain an internal chemical
environment.
• Experiments demonstrate that protobionts
could have formed spontaneously from
abiotically produced organic compounds.
• For example, small membrane-bounded
droplets called liposomes can form when lipids
or other organic molecules are added to water.
Fig. 25-3
Figure 25.3 Laboratory versions of protobionts
20 µm
Glucose-phosphate
Glucose-phosphate
Phosphatase
Starch
Phosphate
(a) Simple reproduction by
liposomes
Amylase
Maltose
Maltose
(b) Simple metabolism
Fig. 25-3a
20 µm
(a) Simple reproduction by
liposomes
Fig. 25-3b
Glucose-phosphate
Glucose-phosphate
Phosphatase
Starch
Amylase
Phosphate
Maltose
Maltose
(b) Simple metabolism
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
their own sequence or other short pieces of
RNA.
• Early protobionts with self-replicating, catalytic
RNA would have been more effective at using
resources and would have increased in number
through natural selection.
• The early genetic material might have formed
an “RNA world.”
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
Fig. 25-4
Present
Rhomaleosaurus victor,
a plesiosaur
Dimetrodon
Casts of
ammonites
Hallucigenia
Coccosteus cuspidatus
Dickinsonia
costata
Stromatolites
Tappania, a
unicellular
eukaryote
Fossilized
stromatolite
Fig. 25-4-1
Hallucigenia
Dickinsonia
costata
Stromatolites
Tappania, a
unicellular
eukaryote
Fossilized
stromatolite
Fig. 25-4a-2
Present
Rhomaleosaurus victor,
a plesiosaur
Dimetrodon
Casts of
ammonites
Coccosteus cuspidatus
Fig. 25-4b
Rhomaleosaurus victor, a plesiosaur
Fig. 25-4c
Dimetrodon
Fig. 25-4d
Casts of ammonites
Fig. 25-4e
Coccosteus cuspidatus
Fig. 25-4f
Hallucigenia
Fig. 25-4g
Dickinsonia costata
2.5 cm
Fig. 25-4h
Tappania, a unicellular eukaryote
Fig. 25-4i
Stromatolites
Fig. 25-4j
Fossilized stromatolite
• 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
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.
Fig. 25-5
1/
2
Remaining
“parent”
isotope
1
Accumulating
“daughter”
isotope
1/
4
1/
3
2
Time (half-lives)
8
1/
4
16
• 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 magnetism of rocks can provide dating
information.
• Reversals of the magnetic poles leave their
record on rocks throughout the world.
The Origin of New Groups of Organisms
• Mammals belong to the group of animals called
tetrapods.
• The evolution of unique mammalian features
through gradual modifications can be traced
from ancestral synapsids through the present.
Fig. 25-6
Synapsid (300 mya)
Temporal
fenestra
Figure 25.6 The origin of mammals
Key
Articular
Quadrate
Dentary
Squamosal
Therapsid (280 mya)
Reptiles
(including
dinosaurs and birds)
Temporal
fenestra
Early cynodont (260 mya)
Later cynodont (220 mya)
Very late cynodont (195 mya)
Dimetrodon
Therapsids
Temporal
fenestra
EARLY
TETRAPODS
Very late cynodonts
Mammals
Fig. 25-6-1
Figure 25.6 The origin of mammals
Synapsid (300 mya)
Temporal
fenestra
Therapsid (280 mya)
Temporal
fenestra
Key
Articular
Quadrate
Dentary
Squamosal
Fig. 25-6-2
Early cynodont (260 mya)
Figure 25.6 The origin of mammals
Key
Temporal
fenestra
Later cynodont (220 mya)
Very late cynodont (195 mya)
Articular
Quadrate
Dentary
Squamosal
Concept 25.3: Key events in life’s history include the
origins of single-celled and multicelled organisms
and the colonization of land.
• The geologic record is divided into the
Archaean, the Proterozoic, and the
Phanerozoic eons.
Table 25-1
Table 25-1a
Table 25-1b
• The Phanerozoic encompasses multicellular
eukaryotic life.
• The Phanerozoic is divided into three eras: the
Paleozoic, Mesozoic, and Cenozoic.
• Major boundaries between geological divisions
correspond to extinction events in the fossil
record.
Humans
Figure 25.7
Clock
analogy for
some key
events in
Earth’s
history
Colonization
of land
Animals
Origin of solar
system and
Earth
4
1
Proterozoic
2
Archaean
3
Multicellular
eukaryotes
Single-celled
eukaryotes
Atmospheric
oxygen
Prokaryotes
The First Single-Celled Organisms
• The oldest known fossils are stromatolites,
rock-like 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 2.1 billion years ago.
Fig 25-UN2
1
4
2
3
Prokaryotes
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.
• The source of O2 was likely bacteria similar to
modern cyanobacteria.
• 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 2.2 billion
years ago:
– Posed a challenge for life.
– Provided opportunity to gain energy from light.
– Allowed organisms to exploit new ecosystems.
Fig 25-UN3
1
4
2
3
Atmospheric
oxygen
Figure 25.8 Banded iron formations: evidence of oxygenic photosynthesis
The First Eukaryotes
• The oldest fossils of eukaryotic cells date back
2.1 billion years.
• The hypothesis of endosymbiosis 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.
Fig 25-UN4
1
4
2
Singlecelled
eukaryotes
3
• 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.
Fig. 25-9-1
Figure 25.9 A model of the origin of eukaryotes through serial endosymbiosis
Plasma membrane
Cytoplasm
Ancestral
prokaryote
DNA
Endoplasmic reticulum
Nuclear envelope
Nucleus
Fig. 25-9-2
Figure 25.9 A model of the origin of eukaryotes through serial endosymbiosis
Aerobic
heterotrophic
prokaryote
Mitochondrion
Ancestral
heterotrophic
eukaryote
Fig. 25-9-3
Figure 25.9 A model of the origin of eukaryotes through serial endosymbiosis
Photosynthetic
prokaryote
Mitochondrion
Plastid
Ancestral photosynthetic
eukaryote
Fig. 25-9-4
Plasma membrane
Cytoplasm
Ancestral
prokaryote
DNA
Endoplasmic reticulum
Nucleus
Nuclear envelope
Aerobic
heterotrophic
prokaryote
Photosynthetic
prokaryote
Mitochondrion
Ancestral
heterotrophic
eukaryote
Mitochondrion
Plastid
Ancestral photosynthetic
eukaryote
• Key evidence supporting an endosymbiotic
origin of mitochondria and plastids:
– Similarities in inner membrane structures and
functions.
– 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.
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.
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 565 to 535 million years ago.
Fig 25-UN5
1
4
2
Multicellular
eukaryotes
3
The Cambrian Explosion
• The Cambrian explosion refers to the sudden
appearance of fossils resembling modern phyla
in the Cambrian period (535 to 525 million
years ago).
• The Cambrian explosion provides the first
evidence of predator-prey interactions.
Fig 25-UN6
Animals
1
4
2
3
Early
Paleozoic
era
(Cambrian
period)
542
Late
Proterozoic
eon
Sponges
500
Arthropods
Molluscs
Annelids
Brachiopods
Chordates
Echinoderms
Cnidarians
Millions of years ago
Fig. 25-10
• 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.”
Fig. 25-11
Figure 25.11 Proterozoic fossils that may be animal embryos (SEM)
(a) Two-cell stage
150 µm
(b) Later stage
200 µm
The Colonization of Land
• Fungi, plants, and animals began to colonize
land about 500 million years ago.
• Plants and fungi likely colonized land together
by 420 million years ago.
• Arthropods and tetrapods are the most
widespread and diverse land animals.
• Tetrapods evolved from lobe-finned fishes
around 365 million years ago.
Fig 25-UN7
Colonization of land
1
4
2
3
Concept 25.4: The rise and fall of dominant groups
reflect continental drift, mass extinctions, and
adaptive radiations.
• The history of life on Earth has seen the rise
and fall of many groups of organisms.
Video: Volcanic Eruption
Video: Lava Flow
Continental Drift
• At three points in time, the land masses of
Earth have formed a supercontinent: 1.1 billion,
600 million, and 250 million years ago.
• Earth’s continents move slowly over the
underlying hot mantle 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.
Fig. 25-12
Figure 25.12 Earth and its continental plates
North
American
Plate
Crust
Juan de Fuca
Plate
Eurasian Plate
Caribbean
Plate
Philippine
Plate
Arabian
Plate
Mantle
Pacific
Plate
Outer
core
Inner
core
(a) Cutaway view of Earth
Indian
Plate
Cocos Plate
Nazca
Plate
South
American
Plate
African
Plate
Scotia Plate
(b) Major continental plates
Antarctic
Plate
Australian
Plate
Fig. 25-12a
Figure 25.12 Earth and its continental plates
Crust
Mantle
Outer
core
Inner
core
(a) Cutaway view of Earth
Fig. 25-12b
Figure 25.12 Earth and its continental plates
North
American
Plate
Juan de Fuca
Plate
Eurasian Plate
Caribbean
Plate
Philippine
Plate
Arabian
Plate
Indian
Plate
Cocos Plate
Pacific
Plate
Nazca
Plate
South
American
Plate
Scotia Plate
(b) Major continental plates
African
Plate
Antarctic
Plate
Australian
Plate
Consequences of Continental Drift
• Formation of the supercontinent Pangaea
about 250 million years ago had many effects.
– A reduction in shallow water habitat.
– A colder and drier climate inland.
– Changes in climate as continents moved
toward and away from the poles.
– Changes in ocean circulation patterns leading
to global cooling.
Cenozoic
Present
Figure 25.13
The history of
continental
drift during the
Phanerozoic
eon
Eurasia
Africa
65.5
South
America
India
Madagascar
251
Mesozoic
135
Paleozoic
Millions of years ago
Antarctica
Cenozoic
Present
Millions of years ago
Figure 25.13
The history of
continental
drift during the
Phanerozoic
eon
65.5
Eurasia
Africa
South
America
India
Madagascar
Antarctica
251
Mesozoic
Paleozoic
Figure 25.13
The history of
continental
drift during the
Phanerozoic
eon
Millions of years ago
135
• The break-up of Pangaea lead to allopatric
speciation.
• The current distribution of fossils reflects the
movement of continental drift.
• 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.
• At times, the rate of extinction has increased
dramatically and caused a mass extinction.
The “Big Five” Mass Extinction Events
• In each of the five mass extinction events,
more than 50% of Earth’s species became
extinct.
Figure 25.14 Mass extinction and the diversity of life
800
700
15
600
500
10
400
300
5
200
100
0
Era
Period
542
E
O
Paleozoic
S
D
488 444 416
359
C
Tr
P
299
251
Mesozoic
C
J
200
145
Time (millions of years ago)
Cenozoic
P
65.5
N
0
0
Number of families:
Total extinction rate
(families per million years):
20
• The Permian extinction defines the boundary
between the Paleozoic and Mesozoic eras.
• This mass extinction occurred in less than 5
million years and caused the extinction of
about 96% of marine animal species.
• This event might have been caused by
volcanism, which lead to global warming, and a
decrease in oceanic oxygen.
• 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.
Fig. 25-15
Figure 25.15 Trauma for Earth and its Cretaceous life
NORTH
AMERICA
Yucatán
Peninsula
Chicxulub
crater
• The presence of iridium in sedimentary rocks
suggests a meteorite impact about 65 million
years ago.
• The Chicxulub crater off the coast of Mexico is
evidence of a meteorite that dates to the same
time.
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.
• Data suggest that a sixth human-caused mass
extinction is likely to occur unless dramatic
action is taken.
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.
• Mass extinction can pave the way for adaptive
radiations.
Fig. 25-16
Predator genera
(percentage of marine genera)
Figure 25.16 Mass extinctions and ecology
50
40
30
20
10
0
Paleozoic
Mesozoic
Era
D
C
P
C
E
O S
J
Tr
Period
359
488 444 416
542
299 251
200
145
Time (millions of years ago)
Cenozoic
P
65.5
N
0
Adaptive Radiations
• Adaptive radiation is the evolution of diversely
adapted species from a common ancestor
upon introduction to new environmental
opportunities.
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 25.17 Adaptive radiation of mammals
Ancestral
mammal
Monotremes
(5 species)
ANCESTRAL
CYNODONT
Marsupials
(324 species)
Eutherians
(placental
mammals;
5,010 species)
250
200
100
150
Millions of years ago
50
0
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.
Figure 25.18 Adaptive radiation on the Hawaiian Islands
Close North American relative,
the tarweed Carlquistia muirii
Dubautia laxa
KAUAI
5.1
million
years
MOLOKAI
OAHU
3.7 LANAI
million
years
1.3
MAUI million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Fig. 25-18a
Figure 25.18 Adaptive radiation on the Hawaiian Islands
KAUAI
5.1
million
years
MOLOKAI
OAHU
3.7
million
years
1.3
MAUI million
years
LANAI
HAWAII
0.4
million
years
Fig. 25-18b
Figure 25.18 Adaptive radiation on the Hawaiian Islands
Close North American relative,
the tarweed Carlquistia muirii
Fig. 25-18c
Figure 25.18 Adaptive radiation on the Hawaiian Islands
Dubautia waialealae
Figure 25.18
Adaptive radiation
on the Hawaiian
Islands
Dubautia laxa
Figure 25.18 Adaptive radiation on the Hawaiian Islands
Figure
25.18
Adaptive
radiation
on the
Hawaiian
Islands
Dubautia scabra
Fig. 25-18f
Figure
25.18
Adaptive
radiation
on the
Hawaiian
Islands
Argyroxiphium sandwicense
Fig. 25-18g
Figure
25.18
Adaptive
radiation
on the
Hawaiian
Islands
Dubautia linearis
Concept 25.5: Major changes in body form can result
from changes in the sequences and regulation of
developmental genes.
• Studying genetic mechanisms of change can
provide insight into large-scale evolutionary
change.
Evolutionary 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 25.19
Relative
growth rates
of body parts
Newborn
2
5
Age (years)
15
Adult
(a) Differential growth rates in a human
Figure 25.19 Relative growth rates of body parts
Chimpanzee fetus
Chimpanzee adult
Human fetus
Human adult
(b) Comparison of chimpanzee and human skull growth
Figure 25.19 Relative growth rates of body parts
Newborn
2
5
Age (years)
15
(a) Differential growth rates in a human
Adult
Figure 25.19
Relative
growth
rates of
body parts
Chimpanzee fetus
Chimpanzee adult
Human fetus
Human adult
(b) Comparison of chimpanzee and human skull growth
• 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.
Fig. 25-20
Figure 25.20 Paedomorphosis
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.
• Evolution of vertebrates from invertebrate
animals was associated with alterations in Hox
genes.
• Two duplications of Hox genes have occurred
in the vertebrate lineage.
• These duplications may have been important in
the evolution of new vertebrate characteristics.
Fig. 25-21
Hypothetical vertebrate
ancestor (invertebrate)
with a single Hox cluster
First Hox
Figure 25.21
Hox
duplication
mutations
and the
origin of
vertebrates
Hypothetical early
vertebrates (jawless)
with two Hox clusters
Second Hox
duplication
Vertebrates (with jaws)
with four Hox clusters
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 sixlegged 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.
Fig. 25-22
Figure 25.22 Origin of the insect body plan
Hox gene 6
Hox gene 7
Hox gene 8
Ubx
About 400 mya
Drosophila
Artemia
Changes in Gene Regulation
• Changes in the form of organisms may be
caused more often by changes in the
regulation of developmental genes instead of
changes in their sequence.
• For example three-spine 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.
Fig. 25-23
RESULTS
Figure 25.23 What causes the loss of
spines in lake stickleback fish?
Test of Hypothesis A:
Differences in the coding
sequence of the Pitx1 gene?
Result:
No
Test of Hypothesis B:
Differences in the regulation
of expression of Pitx1 ?
Result:
Yes
Marine stickleback embryo
Close-up
of mouth
Close-up of ventral surface
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 stickbacks.
Lake stickleback embryo
Fig. 25-23a
Figure 25.23 What causes the loss of
spines in lake stickleback fish?
Marine stickleback embryo
Close-up
of mouth
Close-up of ventral surface
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.
Pigmented
cells
Pigmented cells
(photoreceptors)
Figure
Epithelium
25.24 A
range of eye
Nerve fibers
complexity
(a) Patch of pigmented cells
among
molluscs
Fluid-filled cavity
Epithelium
Optic
nerve
Nerve fibers
(b) Eyecup
Cellular
mass
(lens)
Pigmented
layer (retina)
(c) Pinhole camera-type eye
Cornea
Optic nerve
(d) Eye with primitive lens
Cornea
Lens
Retina
Optic nerve
(e) Complex camera-type eye
Evolutionary Trends
• Extracting a single evolutionary progression
from the fossil record can be misleading.
• Apparent trends should be examined in a
broader context.
Fig. 25-25
Recent
(11,500 ya)
Equus
Pleistocene
(1.8 mya)
Hippidion and other genera
Nannippus
Pliohippus
Pliocene
(5.3 mya)
Hipparion Neohipparion
Sinohippus
Megahippus
Callippus
Archaeohippus
Miocene
(23 mya)
Merychippus
Hypohippus
Anchitherium
Parahippus
Miohippus
Oligocene
(33.9 mya)
Mesohippus
Paleotherium
Epihippus
Propalaeotherium
Eocene
(55.8 mya)
Pachynolophus
Orohippus
Key
Hyracotherium
Grazers
Browsers
Figure 25.25 The branched evolution of horses
Miohippus
Oligocene
(33.9 mya)
Mesohippus
Paleotherium
Epihippus
Propalaeotherium
Eocene
(55.8 mya)
Pachynolophus
Orohippus
Key
Hyracotherium
Grazers
Browsers
Fig. 25-25b
Recent
(11,500 ya)
Equus
Pleistocene
(1.8 mya)
Hippidion and other genera
Nannippus
Pliohippus
Pliocene
(5.3 mya)
Hipparion Neohipparion
Sinohippus
Megahippus
Callippus
Archaeohippus
Miocene
(23 mya)
Merychippus
Anchitherium
Hypohippus
Parahippus
• According to the species selection model,
trends may result when species with certain
characteristics endure longer and speciate
more often than those with other
characteristics.
• The appearance of an evolutionary trend does
not imply that there is some intrinsic drive
toward a particular phenotype.
Fig 25-UN8
1.2 bya:
First multicellular eukaryotes
2.1 bya:
First eukaryotes (single-celled)
535–525 mya:
Cambrian explosion
(great increase
in diversity of
animal forms)
3.5 billion years ago (bya):
First prokaryotes (single-celled)
Millions of years ago (mya)
500 mya:
Colonization
of land by
fungi, plants
and animals
Fig 25-UN9
Origin of solar system
and Earth
4
1
Proterozoic Archaean
2
3
Fig 25-UN10
Flies and
fleas
Caddisflies
Herbivory
Moths and
butterflies
Fig 25-UN11
Origin of solar system
and Earth
4
1
Proterozoic
2
Archaean
3
You should now be able to:
1. Define radiometric dating, serial
endosymbiosis, Pangaea, snowball Earth,
exaptation, heterochrony, and
paedomorphosis.
2. Describe the contributions made by Oparin,
Haldane, Miller, and Urey toward
understanding the origin of organic molecules.
3. Explain why RNA, not DNA, was likely the first
genetic material.
4. Describe and suggest evidence for the major
events in the history of life on Earth from
Earth’s origin to 2 billion years ago.
5. Briefly describe the Cambrian explosion.
6. Explain how continental drift led to Australia’s
unique flora and fauna.
7. Describe the mass extinctions that ended the
Permian and Cretaceous periods.
8. Explain the function of Hox genes.
×

Report this document