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AP Biology 2012
Ch. 25 The History of Life on Earth
“We are like butterflies who
flutter for a day and think it
is forever.” ― Carl Sagan
AP Biology
Bacteria Archae- bacteria
Animalia Fungi Protista Plantae
4500
4000
3500
3000
2500
2000
500
1500
0
1000
Formation of earth
Molten-hot surface of earth becomes cooler
Oldest definite fossils of prokaryotes
Appearance of oxygen in atmosphere
Oldest definite fossils of eukaryotes
First multicellular organisms
Appearance of animals and land plants
Colonization of land by animals Paleozoic
Mesozoic
Cenozoic
Millio
ns
of
ye
ars
ag
o
AR
CH
EA
N
PR
EC
AM
BR
IAN
PR
OT
ER
OZ
OIC
The evolutionary tree of life can be documented with evidence.
The Origin of Life on Earth is another story…
AP Biology
What is Life?
First we have to define LIFE…
organized as cells
respond to stimuli
regulate internal processes homeostasis
use energy to grow metabolism
develop change & mature
within lifetime
reproduce heredity
DNA / RNA
adaptation & evolution
AP Biology
The Origin of Life is Hypothesis Extraterrestrial Origin
Was the original source of organic (carbon) materials comets & meteorites striking early Earth?
testable
Spontaneous Abiotic Origin
Did life evolve spontaneously from inorganic molecules?
testable
AP Biology
Conditions on early Earth
Reducing atmosphere
water vapor (H2O), CO2, N2, NOx, H2, NH3,
CH4, H2S
lots of available H & its electron
no free oxygen!
Energy source
lightning, UV radiation,
volcanic
low O2 =
organic molecules
do not breakdown
as quickly
What’s missing from that
atmosphere?
AP Biology
Water vapor
Condensed liquid with complex, organic molecules
Condenser
Mixture of gases ("primitive atmosphere")
Heated water ("ocean")
Electrodes discharge sparks
(lightning simulation)
Water
Origin of Organic Molecules
Abiotic synthesis
1920 Oparin & Haldane propose reducing atmosphere hypothesis
1953 Miller & Urey test hypothesis formed organic
compounds amino acids
adenine
CH4
NH3 H2
AP Biology
Stanley Miller
University of Chicago
produced
-amino acids
-hydrocarbons
-nitrogen bases
-other organics
It’s ALIVE!
AP Biology
Bubbles… Tiny bubbles…
Origin of Cells (Protobionts) Bubbles separate inside from outside
metabolism & reproduction
AP Biology
Origin of Genetics
RNA is likely first genetic material
multi-functional
codes information self-replicating molecule
makes inheritance possible
natural selection & evolution
enzyme functions ribozymes
replication
regulatory molecule
transport molecule tRNA & mRNA
Dawn of natural selection
AP Biology
Key Events in Origin of Life
Key events in
evolutionary
history of life on
Earth
life originated
3.5–4.0 bya
AP Biology
Prokaryotes
Prokaryotes dominated life
on Earth from 3.5–2.0 bya
3.5 billion year old
fossil of bacteria modern bacteria
chains of one-celled cyanobacteria
AP Biology
Stromatolites Fossilized mats of prokaryotes resemble modern microbial colonies
Lynn Margulis
AP Biology
Oxygen atmosphere Oxygen begins to accumulate 2.7 bya
reducing oxidizing atmosphere evidence in banded iron in rocks = rusting
makes aerobic respiration possible
photosynthetic bacteria (blue-green algae)
AP Biology
First Eukaryotes
Development of internal membranes create internal micro-environments
advantage: specialization = increase efficiency natural selection!
infolding of the plasma membrane
DNA
cell wall
plasma membrane
Prokaryotic cell
Prokaryotic ancestor of eukaryotic
cells
Eukaryotic cell
endoplasmic reticulum (ER)
nuclear envelope
nucleus
plasma membrane
~2 bya
AP Biology
Endosymbiosis
Ancestral eukaryotic cell
Eukaryotic cell with mitochondrion
internal membrane
system aerobic bacterium mitochondrion
Endosymbiosis
Evolution of eukaryotes origin of mitochondria
engulfed aerobic bacteria, but did not digest them
mutually beneficial relationship
natural selection!
AP Biology
mitochondrion
chloroplast
Eukaryotic cell with
chloroplast & mitochondrion
Endosymbiosis
photosynthetic
bacterium
Endosymbiosis
Evolution of eukaryotes origin of chloroplasts
engulfed photosynthetic bacteria, but did not digest them
mutually beneficial relationship natural selection!
Eukaryotic cell with
mitochondrion
AP Biology
Variations in Cell Interior
aerobic bacterium
mitochondria
cyanobacterium
(photosythetic) bacterium
chloroplast
AP Biology
Evidence
structural mitochondria & chloroplasts
resemble bacterial structure
genetic mitochondria & chloroplasts
have their own circular DNA, like bacteria
functional mitochondria & chloroplasts
move freely within the cell
mitochondria & chloroplasts reproduce independently from the cell
Theory of Endosymbiosis
Lynn Margulis
AP Biology
The chimera of Greek
mythology was part goat,
part lion, and part serpent.
The eukaryotic cell is a
“chimera” of prokaryotic
parts:
mitochondria from one bacteria
plastids from another
nuclear genome from the host cell
The eukaryotic cell is a chimera
of prokaryotic ancestors
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology
The first great adaptive radiation, the
metabolic diversification of the prokaryotes,
set the stage for the second.
The second wave of diversification was
greater structural diversity-The Protists.
The third wave of diversification followed the
origin of multicellular bodies in several
eukaryotic lineages- Plants, Fungi, Animals.
The origin of eukaryotes catalyzed a
great waves of diversification
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology
“Evo-devo”: Developmental genes
play a major role in evolution
Genes that program development by controlling the rate, timing, and spatial pattern of changes
Allometric growth
AP Biology
Change the relative rates of growth even
slightly, and you can change the adult
from substantially.
Neoteny- retention of
juvenile features into
adulthood. Note how
in humans we have
kept juvenile facial
features by not
developing heavy
eyebrow ridges and
a snouty upper jaw
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 24.19b
AP Biology
Evolutionary Developmental Biology
Major questions in Evo-Devo How do HOX genes provide positional
information?
How are Gene pathways directed?
How can developments evolve?
AP Biology
Hox Genes Hox (homeobox) genes
control the morphology
of segments in animals.
Discovered in the
70s and 80s
Homeotic selector
genes - control
patterning of
body structures
AP Biology
Mutations in Hox genes
AP Biology
The Homeobox A highly conserved amino acid sequence,
shared among Hox genes, that binds DNA
Thus, Hox genes regulate the transcription
of other genes – typically, genes that are
part of gene cascades involved in
development.
Transcription factor: a protein that, by
interacting with a regulatory DNA sequence,
affects the transcription of the associated
gene
AP Biology
Expression
Occurs in an
anterior-posterior
pattern
Segment-specific
expression in mouse
hindbrain
AP Biology
Anterior-posterior
patterns of HOX
expression: highly
conserved.
AP Biology
How is position-specific expression achieved?
Segmentation genes
establish early embryonic
spatial patterns of
transcription factors.
These transcription factors
drive the spatial pattern of
HOX gene expression.
HOX genes then trigger cascades of developmental
gene pathways (via transcription factors for genes that
influence the expression of yet other genes).
AP Biology
Ancestral Pathway
New Regulatory
Genes
Conserved
Regulatory
Genes
Changed Pattern of
Regulatory Gene
Expression
New Domains
of Expression
Conserved Pattern
Regulatory Gene
Expression
New
Promoter
Affected by
Transcription
Factor
Modification of
Expression within
Conserved
Domain
Change in
Sequence
of Target
Gene
AP Biology
New HOX genes for new segmental morphologies?
Ed Lewis’ model 1978
AP Biology
Hox genes act by regulating multiple target genes
Ubx- regulated expression of
leg development
Less Ubx expression in the
posterior segments of
Drosophila results in
suppression of leg formation.
AP Biology
HOX genes: Regulate multiple target genes
Have distinct sets of downstream targets
Target genes change during evolution,
Changes HOX gene functions
HOX genes are highly conserved
We still know very little about the
downstream targets of the HOX genes
The more things change, the more they stay the same
AP Biology
Evolution is not goal-oriented
An evolutionary trend does not mean that evolution is goal-oriented.
Surviving species do not represent the peak of perfection. There is compromise & random chance involved as well Remember that for humans as well!
Evolution is not the
survival of the fittest.
Rather it is the
survival of the just
good enough.
AP Biology
Cambrian explosion Diversification of Animals
within 10–20 million years most of the major phyla of animals
appear in fossil record
Evolution of hard shells…indicates a new mode of defense
against predators?
543 mya
AP Biology
AP Biology
Plant Diversity
Bryophytes
non-vascular
land plants
Pteridophytes
seedless
vascular plants
Gymnosperm
pollen &
“naked” seeds
Angiosperm
flowers & fruit
pollen & seeds
vascular system = water conduction
mosses ferns
conifers flowering plants
colonization of land
Tracheophytes
xylem cells = tracheids Ancestral Protist
flowers
AP Biology
Animal vs. Plant life cycle
diploid multicellular
individual 2n
diploid multicellular sporophyte
2n
haploid multicellular gametophyte
1n
haploid unicellular gametes
1n
gametes 1n
Animal Plant
alternation of generations
meiosis
fertilization
mitosis
mitosis mitosis
fertilization
mitosis
no multicellular haploid
meiosis
spores 1n zygote 2n
zygote 2n
AP Biology
First land plants-Nonvascular– 450 MYA
Bryophytes: mosses & liverworts
non-vascular
no water transport system
no true roots
swimming sperm
flagellated sperm
lifecycle dominated by
haploid gametophyte stage
fuzzy moss plant you are
familiar with is haploid
spores for reproduction
haploid cells which sprout
to form gametophyte
diploid haploid
Where must mosses live?
AP Biology
First vascular plants – 400 MYA
Pteridophytes: Ferns
vascular water transport system
xylem, phloem, roots, leaves
swimming sperm flagellated sperm
life cycle dominated by sporophyte stage leafy fern plant you are
familiar with is diploid
fragile independent gametophyte (prothallus)
spores for reproduction haploid cells which sprout
to form gametophyte
diploid
Where must ferns live?
haploid
AP Biology
First seed plants – 350 MYA Gymnosperm: conifers
Vascular – xylem and phloem
heterospory male vs. female gametophytes
seeds naked seeds (no fruit)
pollen contain male gametophyte
spread by wind
life cycle dominated by sporophyte stage coniferous trees you are familiar with are diploid
reduced (microscopic) gametophyte
reduction of gametophyte protects delicate egg & embryo in protective sporophyte
protected from drought & UV radiation
AP Biology
First flowering plants – 130 MYA Angiosperm: flowering plants
Vascular – xylem and phloem
heterospory male vs. female gametophytes
flower specialized structure for sexual reproduction
seeds within fruit
Pollen - spread by wind or animals
life cycle dominated by sporophyte stage trees & bushes you are familiar
with are diploid
reduced (microscopic) gametophyte
AP Biology
Co-evolution: flowers & pollinators
The mirror ophrys (Ophrys
speculum) flower resembles
that of the female wasp Colpa
aurea. Males of the species
pick up pollen during their
attempts at copulation.
How a bee sees a flower…insects see
UV light = a bulls-eye to the nectar
AP Biology
Porifera
Cnidaria
Platyhelminthes
sponges jellyfish flatworms roundworms
Nematoda
Mollusca Arthropoda Chordata
Annelida Echinodermata
mollusks
multicellularity
Ancestral Protist
tissues
bilateral symmetry
body cavity
segmentation
Animal Evolution
coelom
starfish vertebrates
endoskeleton
segmented worms
insects spiders
backbone
specialization & body complexity
specialized structure & function,
muscle & nerve tissue
distinct body plan; cephalization
body complexity
digestive & repro sys
digestive sys
body size
redundancy,
specialization, mobility
body & brain
size, mobility
radial
bilateral
AP Biology
Body Cavity ectoderm
ectoderm
mesoderm
endoderm
ectoderm
mesoderm
endoderm
mesoderm
endoderm
acoelomate
pseudocoelomate
coelomate
coelom cavity
pseudocoel
Space for organ system development
increase digestive & reproductive systems
increase food capacity & digestion
increase gamete production
Coelem
mesoderm & endoderm interact during development
allows complex structures to develop in digestive system
ex. stomach
protostome vs. deuterostome
AP Biology
Vertebrates
fish, amphibians, reptiles, birds, mammals
internal bony skeleton
backbone encasing
spinal column
skull-encased brain
deuterostome
postanal tail notochord
hollow dorsal nerve cord
pharyngeal pouches
Chordata
becomes brain & spinal cord
becomes vertebrae
becomes gills or Eustachian tube
becomes tail or tailbone
Oh, look… your first
baby picture!
AP Biology
Urochordates, such as the adult sea squirt (right) have larvae with:
•A hollow, dorsal nerve cord •A notochord
•Pharyngeal pouches •post-anal tail
•Think about this: How could
Evo-Devo lead to the evolution of the vertebrates?
Sometimes,
immaturity pays off!
AP Biology
Vertebrates: Fish salmon, trout, sharks
450 mya
Characteristics
body structure
bony & cartilaginous skeleton
jaws & paired appendages (fins)
scales
body function
gills for gas exchange
two-chambered heart;
single loop blood circulation
Ectotherms
gills
body
AP Biology
Evolution of Jaws – about 475 Million years ago. First set of gill
arches were modified into a early set of jaws.
AP Biology
Vertebrates: Fish salmon, trout, sharks
450 mya
Characteristics
reproduction
External fertilization, but three means of delivery…
Oviparous- external development in
aquatic egg outside the body.
Ovoviviparous- retain fertilized eggs in the oviduct.
Viviparous- provide nutrients to the developing
offspring.
buoyancy
Sharks/Rays – use oily liver
Boney Fish – use swim bladder
AP Biology
Transition to Land
Evolution of tetrapods
Tibia
Femur
Fibula
Humerus Shoulder
Radius Ulna
Tibia
Femur Pelvis
Fibula Lobe-finned fish
Humerus
Shoulder
Radius
Ulna
Pelvis
Early amphibian
This reminds me of tadpoles, not
that I’ve ever seen one in Anarctica
AP Biology
lung
buccal cavity
glottis closed
Vertebrates: Amphibian
Characteristics
body structure legs (tetrapods)
moist , porous skin
body function lungs (positive pressure) &
diffusion through skin for gas exchange
three-chambered heart; veins from lungs back to heart
ectotherms
reproduction external fertilization (Oviparous)
external development in aquatic egg
metamorphosis (tadpole to adult)
frogs
salamanders
toads
350 mya
AP Biology
Amphibian Metamorphosis
Transitions from a fish-like creature
to a land-living creature.
•Gills,lateral line, fin,
swim bladder
•Gills- replaced with lungs
•Lateral line disappears
•Fin replaced with legs
•Swim bladder turns
into lungs
AP Biology
Amphibian Circulatory System
Two-chambered heart
as tadpole
Three-chambered heart as adult
Note: oxygenated blood mixes with CO2-carrying blood in the
ventricle-not so efficient, but good enough if you’re ectothermic.
AP Biology
Vertebrates: Reptiles Characteristics
body structure dry skin, scales, armor
body function lungs for gas exchange
thoracic breathing; negative pressure
three-chambered heart
ectotherms
reproduction internal fertilization
external development in amniotic egg
250 mya dinosaurs, turtles
lizards, snakes
alligators, crocodile
embryo leathery shell
chorion
allantois yolk sac
amnion
AP Biology
AP Biology
The amniote clade consists of the mammals, the birds, and
the vertebrates commonly called reptiles, including turtles,
lizards, snakes, and crocodiles.
The evolution of amniotes from an amphibian ancestor
involved many adaptations for terrestrial living including:
the amniotic egg
waterproof skin
increasing use of the rib cage to ventilate the lungs
as skin was no longer useful for respiration.
Evolution of the amniotic egg expanded
the success of vertebrates on land
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology
The amniotic eggs enabled terrestrial vertebrates to
complete their life cycles entirely on land.
Reptile eggs have a leathery shell that retains
water and can be laid in a dry place.
The calcareous shells of bird eggs are inflexible,
while the leathery eggs of many reptiles are
flexible.
Most mammals have dispensed with the shell.
The embryo implants in the wall of the uterus
and obtains its nutrition from the mother.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology
Inside the shell of the amniotic egg are several
extraembryonic membranes that function in gas exchange,
waste storage, and the transfer of stored nutrients to the
embryo.
These develop from tissues layers that grow out
from the embryo.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 34.19
AP Biology
Vertebrates: Birds (Aves) Characteristics
body structure feathers & wings
thin, hollow bone; flight skeleton
body function very efficient lungs & air sacs
four-chambered heart
endotherms
reproduction internal fertilization
external development in amniotic egg
150 mya finches, hawk
ostrich, turkey
trachea
anterior air sacs
lung
posterior air sacs
AP Biology
AP Biology
The most obvious adaptations for flight are wings.
Wings are airfoils that illustrate the same principles of
aerodynamics as airplane wings.
Pressure differences created by differences in air flow over the top (low pressure) and bottom of the convex wing (high pressure) lift the wing and the bird.
Large pectoral (breast) muscles anchored to a keel on the sternum (breastbone) power flapping of the wings.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 34.26
AP Biology
Vertebrates: Mammals
220 mya / 65 mya mice, ferret
elephants, bats
whales, humans
muscles contract
diaphragm contracts
Characteristics
body structure hair
specialized teeth
body function lungs, diaphragm; negative pressure
four-chambered heart
endotherms
reproduction internal fertilization
internal development in uterus
nourishment through placenta
birth live young
mammary glands make milk
AP Biology
Feeding adaptations of the jaws and teeth are
other important mammalian traits.
teeth of mammals come in a variety of
shapes and sizes adapted for processing
many kinds of foods.
During the evolution of mammals from
reptiles, two bones formerly in the jaw joint
were incorporated into the mammalian ear
and the jaw joint remodeled.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology
Specialized teeth:
Herbivores -Sharp incisors
-Flat molars
-No canines
Carnivores -sharp canines
-sharp, shearing molars
AP Biology Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 34.30
AP Biology
Vertebrates: Mammals Sub-groups
monotremes egg-laying mammals
lack placenta & true nipples
duckbilled platypus, echidna
marsupials pouched mammals
offspring feed from nipples in pouch
short-lived placenta
koala, kangaroo, opossum
placental true placenta
nutrient & waste filter
shrews, bats, whales, humans
AP Biology
AP Biology
Diversity of life & periods of mass extinction
Cambrian
explosion
The fossil
record
records five
to seven
severe mass
extinctions.
AP Biology
Permian mass extinction (250 million years ago)
claimed about 90% of all marine species.
occurred in less than five million years.
thought to have been caused by the effects of a huge
mantle plume that reached the surface in central Siberia,
generating thousands of square miles of lava several
thousand feet thick.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology Copyright © 2002 Pearson Education, Inc., publishing as Benjamin
Cummings
The Cretaceous mass extinction (65 million years ago) -
half of the marine species and many families of terrestrial plants and animals, including nearly all the dinosaur lineages.
Hypotheses for this extinction include:
The climate became cooler, and shallow seas (Sundance Sea) receded from continental lowlands.
Large volcanic eruptions in India (Deccan Traps) may have contributed to global cooling by releasing material into the atmosphere.
And….
AP Biology Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Comet or Asteroid Impact-
Walter and Luis Alvarez – discovered a
thin layer of clay enriched with iridium,
an element rare on Earth but common in
meteorites and other extraterrestrial
debris in deposits of the K/T boundary.
Proposed an asteroid impact that
produced a great cloud that would have
blocked sunlight and disturbed the
climate for several months.
Recent research has focused on the
110 km wide Chicxulub crater, a 65-
million-year-old scar located beneath
sediments on the Yucatan coast of
Mexico.
AP Biology
Diversification of the
surviving groups
result as producer
communities recover
and new niches open
up. Organisms then
“rapidly” evolve to
take advantage of
those niches, along
with their prey,
predators, parasites,
etc….
Mass extinctions are followed by
Adaptive Radiations.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
AP Biology
Early mammal evolution
125 mya mammals
began to radiate
out & fill niches.
However, at no time before the
end of the Cretaceous did any
mammal weigh more than 30 pounds.
AP Biology 2008-2009
Any Questions??
Is there life elsewhere?
Does it look like life on Earth?